<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2023 Workiva-->
<!--r:da244980-6981-484f-a56b-7918256d2acf,g:df9d76e9-e892-49f8-b6a5-c1b4acd11896-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://aquestive.com/role/CondensedConsolidatedStatementsofChangesinStockholdersDeficit" xlink:type="simple" xlink:href="aqst-20230630.xsd#CondensedConsolidatedStatementsofChangesinStockholdersDeficit"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/CondensedConsolidatedStatementsofChangesinStockholdersDeficit" xlink:type="extended" id="i47205b7369aa415caee04fe11f08bc1d_CondensedConsolidatedStatementsofChangesinStockholdersDeficit">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_73b68f81-ed14-4c19-b6f5-cefaf7a21ccf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b68f81-ed14-4c19-b6f5-cefaf7a21ccf" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_c33af5be-ef08-4662-8352-c997ec827194" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_SharesOutstanding_c33af5be-ef08-4662-8352-c997ec827194" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_3c7100ef-ff72-48bb-ac04-fe14aaaad21a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_StockholdersEquity_3c7100ef-ff72-48bb-ac04-fe14aaaad21a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AdjustmentsToAdditionalPaidInCapitalFairValueOfWarrantsIssued_335b9096-efae-49b3-afda-2e9949c92564" xlink:href="aqst-20230630.xsd#aqst_AdjustmentsToAdditionalPaidInCapitalFairValueOfWarrantsIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_aqst_AdjustmentsToAdditionalPaidInCapitalFairValueOfWarrantsIssued_335b9096-efae-49b3-afda-2e9949c92564" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_10717f5b-cc86-41ca-b149-4f60496feb0a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_10717f5b-cc86-41ca-b149-4f60496feb0a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_8f6279fe-c322-4202-9b5a-24098379bb83" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_8f6279fe-c322-4202-9b5a-24098379bb83" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedOwnshareLendingArrangementIssuanceCosts_e7c5922c-1091-463b-aec3-5bde9f7dd265" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedOwnshareLendingArrangementIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedOwnshareLendingArrangementIssuanceCosts_e7c5922c-1091-463b-aec3-5bde9f7dd265" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_873efb17-4ab1-425e-9291-c3a326b9ce3c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_873efb17-4ab1-425e-9291-c3a326b9ce3c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_292b57d2-7dac-4dde-a095-0ea7ff15c2f9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_292b57d2-7dac-4dde-a095-0ea7ff15c2f9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f5ac47ea-4402-41a4-8b37-ebb0a8f3adb2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f5ac47ea-4402-41a4-8b37-ebb0a8f3adb2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_264c0551-bccf-49a7-b7ff-4869b2a3709a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_264c0551-bccf-49a7-b7ff-4869b2a3709a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_0f489cd2-8d59-412b-b586-58f7585ac83d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_0f489cd2-8d59-412b-b586-58f7585ac83d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_3457b88a-1197-49c8-9767-49b7f5d08acb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_StockholdersEquityOther_3457b88a-1197-49c8-9767-49b7f5d08acb" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_1a71d842-a55f-44ec-9148-48e029c58d52" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_be1f4c9f-d54b-4ff0-89a1-6c158fbe5d4c" xlink:to="loc_us-gaap_NetIncomeLoss_1a71d842-a55f-44ec-9148-48e029c58d52" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_fd56296d-d202-4dcd-906e-38e915586c36" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_4ed188db-bd6c-414c-a22f-788ef760b5a0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_41d9851d-f3af-4232-993a-831468a88cf5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_73b68f81-ed14-4c19-b6f5-cefaf7a21ccf" xlink:to="loc_us-gaap_StatementTable_41d9851d-f3af-4232-993a-831468a88cf5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_655e6fde-f5a6-4fa6-9f02-8189acae5bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_41d9851d-f3af-4232-993a-831468a88cf5" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_655e6fde-f5a6-4fa6-9f02-8189acae5bf6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_655e6fde-f5a6-4fa6-9f02-8189acae5bf6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_655e6fde-f5a6-4fa6-9f02-8189acae5bf6" xlink:to="loc_us-gaap_EquityComponentDomain_655e6fde-f5a6-4fa6-9f02-8189acae5bf6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_acdbfe0a-2642-4986-a249-0d00dd04458a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_655e6fde-f5a6-4fa6-9f02-8189acae5bf6" xlink:to="loc_us-gaap_EquityComponentDomain_acdbfe0a-2642-4986-a249-0d00dd04458a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_59dd0710-3d7e-4bae-9618-e798c16a7cbb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_acdbfe0a-2642-4986-a249-0d00dd04458a" xlink:to="loc_us-gaap_CommonStockMember_59dd0710-3d7e-4bae-9618-e798c16a7cbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_03149b84-8735-4d62-b76f-4971e4c4429f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_acdbfe0a-2642-4986-a249-0d00dd04458a" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_03149b84-8735-4d62-b76f-4971e4c4429f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_c30ab055-22c3-42c5-b8c5-fb594371f222" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_acdbfe0a-2642-4986-a249-0d00dd04458a" xlink:to="loc_us-gaap_RetainedEarningsMember_c30ab055-22c3-42c5-b8c5-fb594371f222" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_IssuanceAxis_da865428-dcd0-464b-8249-2d1ab9f62f97" xlink:href="aqst-20230630.xsd#aqst_IssuanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_41d9851d-f3af-4232-993a-831468a88cf5" xlink:to="loc_aqst_IssuanceAxis_da865428-dcd0-464b-8249-2d1ab9f62f97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_IssuanceDomain_da865428-dcd0-464b-8249-2d1ab9f62f97_default" xlink:href="aqst-20230630.xsd#aqst_IssuanceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aqst_IssuanceAxis_da865428-dcd0-464b-8249-2d1ab9f62f97" xlink:to="loc_aqst_IssuanceDomain_da865428-dcd0-464b-8249-2d1ab9f62f97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_IssuanceDomain_cb7ca8fa-64c6-41cf-b8a8-7ab11bb3e050" xlink:href="aqst-20230630.xsd#aqst_IssuanceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aqst_IssuanceAxis_da865428-dcd0-464b-8249-2d1ab9f62f97" xlink:to="loc_aqst_IssuanceDomain_cb7ca8fa-64c6-41cf-b8a8-7ab11bb3e050" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_PublicEquityMember_44a0b1d3-094e-4f96-a89c-035af0cf5017" xlink:href="aqst-20230630.xsd#aqst_PublicEquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_IssuanceDomain_cb7ca8fa-64c6-41cf-b8a8-7ab11bb3e050" xlink:to="loc_aqst_PublicEquityMember_44a0b1d3-094e-4f96-a89c-035af0cf5017" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_PrivateEquityMember_a14301cf-2829-4d72-84ba-8f0cd9e2d1ba" xlink:href="aqst-20230630.xsd#aqst_PrivateEquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_IssuanceDomain_cb7ca8fa-64c6-41cf-b8a8-7ab11bb3e050" xlink:to="loc_aqst_PrivateEquityMember_a14301cf-2829-4d72-84ba-8f0cd9e2d1ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_WarrantExercisesMember_8afa89dd-1156-49ad-afd5-9150599207b4" xlink:href="aqst-20230630.xsd#aqst_WarrantExercisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_IssuanceDomain_cb7ca8fa-64c6-41cf-b8a8-7ab11bb3e050" xlink:to="loc_aqst_WarrantExercisesMember_8afa89dd-1156-49ad-afd5-9150599207b4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/CompanyOverviewandBasisofPresentationDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#CompanyOverviewandBasisofPresentationDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/CompanyOverviewandBasisofPresentationDetails" xlink:type="extended" id="i3c4f0c8aa1c6414d899d5abe5882d722_CompanyOverviewandBasisofPresentationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SaleOfStockAggregateOfferingPrice_7ad3b2b9-4c25-4619-ad60-947abd93089c" xlink:href="aqst-20230630.xsd#aqst_SaleOfStockAggregateOfferingPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_SaleOfStockAggregateOfferingPrice_7ad3b2b9-4c25-4619-ad60-947abd93089c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_a150821e-a6b1-44b9-b806-d300b9846a42" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_a150821e-a6b1-44b9-b806-d300b9846a42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_29393a57-a0cb-448f-8575-f4c024b8d770" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_29393a57-a0cb-448f-8575-f4c024b8d770" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_44024aed-07c7-4dea-a4a7-f2ca7cff31a0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_44024aed-07c7-4dea-a4a7-f2ca7cff31a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_e607cf75-2fc7-40d5-bbf4-f9485754147c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_e607cf75-2fc7-40d5-bbf4-f9485754147c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SaleOfStockRemainingAmountAvailableForOffering_9f0efa62-e3aa-42b7-a298-6494d478c96e" xlink:href="aqst-20230630.xsd#aqst_SaleOfStockRemainingAmountAvailableForOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_SaleOfStockRemainingAmountAvailableForOffering_9f0efa62-e3aa-42b7-a298-6494d478c96e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_RightToSellCommonStockValue_e1abb6f5-7180-47c2-812b-977c873f0d58" xlink:href="aqst-20230630.xsd#aqst_RightToSellCommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_RightToSellCommonStockValue_e1abb6f5-7180-47c2-812b-977c873f0d58" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipLimitationAfterAllTransactions_855c008e-4582-4242-a346-fb0fdf9c6294" xlink:href="aqst-20230630.xsd#aqst_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipLimitationAfterAllTransactions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipLimitationAfterAllTransactions_855c008e-4582-4242-a346-fb0fdf9c6294" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AgreementTerm_2c1688cd-7aec-4b6a-b2a4-344a0deae8fc" xlink:href="aqst-20230630.xsd#aqst_AgreementTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_AgreementTerm_2c1688cd-7aec-4b6a-b2a4-344a0deae8fc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_f0553b0b-a7f7-402d-aac5-f3914b0327e8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_f0553b0b-a7f7-402d-aac5-f3914b0327e8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SharesOfCommonStockEntitledToPurchasersByPreFundedWarrants_90b958dc-5d12-4f15-b38f-8b38c858925d" xlink:href="aqst-20230630.xsd#aqst_SharesOfCommonStockEntitledToPurchasersByPreFundedWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_SharesOfCommonStockEntitledToPurchasersByPreFundedWarrants_90b958dc-5d12-4f15-b38f-8b38c858925d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SharesOfCommonStockToBePurchasedByCommonStockWarrants_026172af-f60f-4043-89b4-de935e9c23a1" xlink:href="aqst-20230630.xsd#aqst_SharesOfCommonStockToBePurchasedByCommonStockWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_SharesOfCommonStockToBePurchasedByCommonStockWarrants_026172af-f60f-4043-89b4-de935e9c23a1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NetProceedsAfterPlacementAgentFeesExpensesAndOfferingExpensesPayable_96d0b162-69aa-421c-8704-39f18e5a4c98" xlink:href="aqst-20230630.xsd#aqst_NetProceedsAfterPlacementAgentFeesExpensesAndOfferingExpensesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_NetProceedsAfterPlacementAgentFeesExpensesAndOfferingExpensesPayable_96d0b162-69aa-421c-8704-39f18e5a4c98" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod_e4961f8b-b440-44dd-b730-2a5bc98cd13c" xlink:href="aqst-20230630.xsd#aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod_e4961f8b-b440-44dd-b730-2a5bc98cd13c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromWarrantExercises_53622606-319b-4afc-a1d0-569ac33c49a0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromWarrantExercises"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_us-gaap_ProceedsFromWarrantExercises_53622606-319b-4afc-a1d0-569ac33c49a0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_21408499-0a6e-44d7-a52a-9fa14d14b46e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_e2862ad6-ac19-4c2e-bed9-23e95d8146d4" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_21408499-0a6e-44d7-a52a-9fa14d14b46e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_6a80e8ba-e726-4373-ad30-b077cf66ddae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_21408499-0a6e-44d7-a52a-9fa14d14b46e" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_6a80e8ba-e726-4373-ad30-b077cf66ddae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_6a80e8ba-e726-4373-ad30-b077cf66ddae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_6a80e8ba-e726-4373-ad30-b077cf66ddae" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_6a80e8ba-e726-4373-ad30-b077cf66ddae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_6a80e8ba-e726-4373-ad30-b077cf66ddae" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_EquityDistributionAgreementMember_28d30c50-7bc9-4a4a-9ed1-d006ff878aba" xlink:href="aqst-20230630.xsd#aqst_EquityDistributionAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:to="loc_aqst_EquityDistributionAgreementMember_28d30c50-7bc9-4a4a-9ed1-d006ff878aba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AtTheMarketOfferingAmendmentOneMember_7afeba7d-7ac3-4ac4-9c2d-f9837aa7fcbf" xlink:href="aqst-20230630.xsd#aqst_AtTheMarketOfferingAmendmentOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:to="loc_aqst_AtTheMarketOfferingAmendmentOneMember_7afeba7d-7ac3-4ac4-9c2d-f9837aa7fcbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AtTheMarketOfferingMember_479ceab8-9a55-4e13-a4f2-0cc6fa18c7c6" xlink:href="aqst-20230630.xsd#aqst_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:to="loc_aqst_AtTheMarketOfferingMember_479ceab8-9a55-4e13-a4f2-0cc6fa18c7c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LincolnParkAgreementMember_61721a7e-f956-4406-bca1-02e95c37ba5d" xlink:href="aqst-20230630.xsd#aqst_LincolnParkAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:to="loc_aqst_LincolnParkAgreementMember_61721a7e-f956-4406-bca1-02e95c37ba5d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SecuritiesPurchaseAgreementMember_e12fa081-c2a6-450f-94e9-2ca95313ba3e" xlink:href="aqst-20230630.xsd#aqst_SecuritiesPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:to="loc_aqst_SecuritiesPurchaseAgreementMember_e12fa081-c2a6-450f-94e9-2ca95313ba3e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LincolnParkAgreementCommitmentShareMember_aeeefdba-eaad-427b-a871-01b956d407e0" xlink:href="aqst-20230630.xsd#aqst_LincolnParkAgreementCommitmentShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c4ed2f2a-ee20-459b-90d6-4d718fad6ba3" xlink:to="loc_aqst_LincolnParkAgreementCommitmentShareMember_aeeefdba-eaad-427b-a871-01b956d407e0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_f1784f71-e384-4aea-b2bf-391a2bda5c23" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_21408499-0a6e-44d7-a52a-9fa14d14b46e" xlink:to="loc_srt_RangeAxis_f1784f71-e384-4aea-b2bf-391a2bda5c23" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f1784f71-e384-4aea-b2bf-391a2bda5c23_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_f1784f71-e384-4aea-b2bf-391a2bda5c23" xlink:to="loc_srt_RangeMember_f1784f71-e384-4aea-b2bf-391a2bda5c23_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_83f19792-766f-498c-b692-09b192fa0090" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_f1784f71-e384-4aea-b2bf-391a2bda5c23" xlink:to="loc_srt_RangeMember_83f19792-766f-498c-b692-09b192fa0090" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_e05ef6ff-f0d0-4641-9db8-298d82d1eb6e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_83f19792-766f-498c-b692-09b192fa0090" xlink:to="loc_srt_MaximumMember_e05ef6ff-f0d0-4641-9db8-298d82d1eb6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_c865f885-4072-44a6-acc3-8579857cf233" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_21408499-0a6e-44d7-a52a-9fa14d14b46e" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_c865f885-4072-44a6-acc3-8579857cf233" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_c865f885-4072-44a6-acc3-8579857cf233_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_c865f885-4072-44a6-acc3-8579857cf233" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_c865f885-4072-44a6-acc3-8579857cf233_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_0c5c3e0a-d452-463b-a2ae-5cfe2ae73568" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_c865f885-4072-44a6-acc3-8579857cf233" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_0c5c3e0a-d452-463b-a2ae-5cfe2ae73568" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_CommonStockWarrantsMember_368d2c64-ac17-4107-8a96-4ae489075d09" xlink:href="aqst-20230630.xsd#aqst_CommonStockWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_0c5c3e0a-d452-463b-a2ae-5cfe2ae73568" xlink:to="loc_aqst_CommonStockWarrantsMember_368d2c64-ac17-4107-8a96-4ae489075d09" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/RisksandUncertaintiesDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#RisksandUncertaintiesDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/RisksandUncertaintiesDetails" xlink:type="extended" id="ieca0d19f6bcc429db1c98d847e8cad62_RisksandUncertaintiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_704cb3f8-79a3-4ed0-9da8-dff91880b1d5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_704cb3f8-79a3-4ed0-9da8-dff91880b1d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_8c8f79cd-b2ab-4251-aadc-aac09ea13640" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_8c8f79cd-b2ab-4251-aadc-aac09ea13640" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_492a26a7-0e19-4f2a-bb9f-ab59eb274e4f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_492a26a7-0e19-4f2a-bb9f-ab59eb274e4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_103737f4-2821-4ddb-b7d8-d5a089917d45" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_103737f4-2821-4ddb-b7d8-d5a089917d45" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_8f733597-e57e-4ff4-93e9-e341ac36e53e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_8f733597-e57e-4ff4-93e9-e341ac36e53e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SaleOfStockRemainingAmountAvailableForOffering_f3c93fb9-17b7-49e4-b800-58b884309738" xlink:href="aqst-20230630.xsd#aqst_SaleOfStockRemainingAmountAvailableForOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_aqst_SaleOfStockRemainingAmountAvailableForOffering_f3c93fb9-17b7-49e4-b800-58b884309738" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_025181e5-427b-4ad2-910c-716552cf010f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_025181e5-427b-4ad2-910c-716552cf010f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_fc823905-c388-45ed-9fde-a43c4ba40e19" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_d0454d17-1044-4475-87a0-e93b9c0ab017" xlink:to="loc_us-gaap_ConcentrationRiskTable_fc823905-c388-45ed-9fde-a43c4ba40e19" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_54dceae5-2d0c-457a-8e36-fd9db8aade51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_fc823905-c388-45ed-9fde-a43c4ba40e19" xlink:to="loc_us-gaap_DebtInstrumentAxis_54dceae5-2d0c-457a-8e36-fd9db8aade51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_54dceae5-2d0c-457a-8e36-fd9db8aade51_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_54dceae5-2d0c-457a-8e36-fd9db8aade51" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_54dceae5-2d0c-457a-8e36-fd9db8aade51_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_173cb410-b887-454f-9c6c-6751b7856eb5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_54dceae5-2d0c-457a-8e36-fd9db8aade51" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_173cb410-b887-454f-9c6c-6751b7856eb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_7f305d58-f6db-47d3-b04f-804691f79281" xlink:href="aqst-20230630.xsd#aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_173cb410-b887-454f-9c6c-6751b7856eb5" xlink:to="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_7f305d58-f6db-47d3-b04f-804691f79281" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_681d40f8-b7fa-45b7-bcf4-79767d93e5af" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_fc823905-c388-45ed-9fde-a43c4ba40e19" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_681d40f8-b7fa-45b7-bcf4-79767d93e5af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_681d40f8-b7fa-45b7-bcf4-79767d93e5af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_681d40f8-b7fa-45b7-bcf4-79767d93e5af" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_681d40f8-b7fa-45b7-bcf4-79767d93e5af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_13a523df-1720-4671-ae4e-ba4bcfb8c3aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_681d40f8-b7fa-45b7-bcf4-79767d93e5af" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_13a523df-1720-4671-ae4e-ba4bcfb8c3aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AtTheMarketOfferingMember_c5fa8f61-c338-48bd-b0eb-d40a1d734889" xlink:href="aqst-20230630.xsd#aqst_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_13a523df-1720-4671-ae4e-ba4bcfb8c3aa" xlink:to="loc_aqst_AtTheMarketOfferingMember_c5fa8f61-c338-48bd-b0eb-d40a1d734889" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_EquityDistributionAgreementMember_d41ff3cd-d5e6-45d9-a178-598c01ac24dc" xlink:href="aqst-20230630.xsd#aqst_EquityDistributionAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_13a523df-1720-4671-ae4e-ba4bcfb8c3aa" xlink:to="loc_aqst_EquityDistributionAgreementMember_d41ff3cd-d5e6-45d9-a178-598c01ac24dc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/RevenuesandTradeReceivablesNetNarrativeDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#RevenuesandTradeReceivablesNetNarrativeDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/RevenuesandTradeReceivablesNetNarrativeDetails" xlink:type="extended" id="i57aca6972a0c4e5d8a2fd4d8191f7be9_RevenuesandTradeReceivablesNetNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ResearchAndDevelopmentProjectDuration_efa3ecc8-cdaf-41d3-a1ec-f2e92240dbd4" xlink:href="aqst-20230630.xsd#aqst_ResearchAndDevelopmentProjectDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:to="loc_aqst_ResearchAndDevelopmentProjectDuration_efa3ecc8-cdaf-41d3-a1ec-f2e92240dbd4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivablesGrossCurrent_8a32b928-5311-4a06-9fa7-d3d2da6f512f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherReceivablesGrossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:to="loc_us-gaap_OtherReceivablesGrossCurrent_8a32b928-5311-4a06-9fa7-d3d2da6f512f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_73f0177d-0c54-42db-b312-235b93ac7c22" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:to="loc_us-gaap_ContractWithCustomerLiability_73f0177d-0c54-42db-b312-235b93ac7c22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AccountsReceivableAllowancesAndAccrualsTradeAndOtherReceivablesNet_b4dc1968-65fa-4475-8456-c60d0a71149e" xlink:href="aqst-20230630.xsd#aqst_AccountsReceivableAllowancesAndAccrualsTradeAndOtherReceivablesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:to="loc_aqst_AccountsReceivableAllowancesAndAccrualsTradeAndOtherReceivablesNet_b4dc1968-65fa-4475-8456-c60d0a71149e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AccountsReceivableAllowancesAndAccrualsAccountsPayableAndAccruedExpenses_219186d9-98da-4685-b15c-ddaae9773022" xlink:href="aqst-20230630.xsd#aqst_AccountsReceivableAllowancesAndAccrualsAccountsPayableAndAccruedExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:to="loc_aqst_AccountsReceivableAllowancesAndAccrualsAccountsPayableAndAccruedExpenses_219186d9-98da-4685-b15c-ddaae9773022" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_345fbe57-5ac0-4be5-9342-a7e778f99215" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_345fbe57-5ac0-4be5-9342-a7e778f99215" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_0c52fda4-bc5f-4c51-92be-cb0438b71f0e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_81feb666-85d9-4783-b8fc-05ebd2ccd1ac" xlink:to="loc_us-gaap_ConcentrationRiskTable_0c52fda4-bc5f-4c51-92be-cb0438b71f0e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_39522e67-ffa2-44ec-8d0b-6fac78f16b66" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0c52fda4-bc5f-4c51-92be-cb0438b71f0e" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_39522e67-ffa2-44ec-8d0b-6fac78f16b66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_39522e67-ffa2-44ec-8d0b-6fac78f16b66_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_39522e67-ffa2-44ec-8d0b-6fac78f16b66" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_39522e67-ffa2-44ec-8d0b-6fac78f16b66_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0b926108-d6e0-472a-9445-580d12fcff1c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_39522e67-ffa2-44ec-8d0b-6fac78f16b66" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0b926108-d6e0-472a-9445-580d12fcff1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_0f004e03-df78-485f-a080-50d1d76b4a79" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0b926108-d6e0-472a-9445-580d12fcff1c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_0f004e03-df78-485f-a080-50d1d76b4a79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_30937d84-ef8c-409e-80d2-b0dd2e529ef9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0b926108-d6e0-472a-9445-580d12fcff1c" xlink:to="loc_us-gaap_AccountsReceivableMember_30937d84-ef8c-409e-80d2-b0dd2e529ef9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_8d0dabbf-d833-48b6-b450-3b4461202bda" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0c52fda4-bc5f-4c51-92be-cb0438b71f0e" xlink:to="loc_srt_MajorCustomersAxis_8d0dabbf-d833-48b6-b450-3b4461202bda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_8d0dabbf-d833-48b6-b450-3b4461202bda_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_8d0dabbf-d833-48b6-b450-3b4461202bda" xlink:to="loc_srt_NameOfMajorCustomerDomain_8d0dabbf-d833-48b6-b450-3b4461202bda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_e61a7cd4-d606-4aed-9d04-3f1a18669c12" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_8d0dabbf-d833-48b6-b450-3b4461202bda" xlink:to="loc_srt_NameOfMajorCustomerDomain_e61a7cd4-d606-4aed-9d04-3f1a18669c12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_CommercialExploitationAgreementWithIndiviorMember_5cd7f58c-cd54-44f0-be02-3f8c6be643d8" xlink:href="aqst-20230630.xsd#aqst_CommercialExploitationAgreementWithIndiviorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_e61a7cd4-d606-4aed-9d04-3f1a18669c12" xlink:to="loc_aqst_CommercialExploitationAgreementWithIndiviorMember_5cd7f58c-cd54-44f0-be02-3f8c6be643d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_HyperaMember_57d099e2-509a-4f1a-a7d3-57fd7d85b336" xlink:href="aqst-20230630.xsd#aqst_HyperaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_e61a7cd4-d606-4aed-9d04-3f1a18669c12" xlink:to="loc_aqst_HyperaMember_57d099e2-509a-4f1a-a7d3-57fd7d85b336" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_2c671b99-1890-4e82-8513-16882c7be829" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0c52fda4-bc5f-4c51-92be-cb0438b71f0e" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_2c671b99-1890-4e82-8513-16882c7be829" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_2c671b99-1890-4e82-8513-16882c7be829_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_2c671b99-1890-4e82-8513-16882c7be829" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_2c671b99-1890-4e82-8513-16882c7be829_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_14b5769f-ca7e-49dc-988c-ab00bc93b142" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_2c671b99-1890-4e82-8513-16882c7be829" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_14b5769f-ca7e-49dc-988c-ab00bc93b142" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_3a2df261-535e-4021-b6c2-88da81399ecd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_14b5769f-ca7e-49dc-988c-ab00bc93b142" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_3a2df261-535e-4021-b6c2-88da81399ecd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_bfbd83c9-ef0c-45c2-845a-edb19af8ba35" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0c52fda4-bc5f-4c51-92be-cb0438b71f0e" xlink:to="loc_srt_RangeAxis_bfbd83c9-ef0c-45c2-845a-edb19af8ba35" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_bfbd83c9-ef0c-45c2-845a-edb19af8ba35_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_bfbd83c9-ef0c-45c2-845a-edb19af8ba35" xlink:to="loc_srt_RangeMember_bfbd83c9-ef0c-45c2-845a-edb19af8ba35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_72f558bf-7243-47b0-a9a5-3b93d03eba8e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_bfbd83c9-ef0c-45c2-845a-edb19af8ba35" xlink:to="loc_srt_RangeMember_72f558bf-7243-47b0-a9a5-3b93d03eba8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_24f4c393-9c1f-430f-a0bf-79be578aa2d0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_72f558bf-7243-47b0-a9a5-3b93d03eba8e" xlink:to="loc_srt_MaximumMember_24f4c393-9c1f-430f-a0bf-79be578aa2d0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/RevenuesandTradeReceivablesNetRevenueDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#RevenuesandTradeReceivablesNetRevenueDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/RevenuesandTradeReceivablesNetRevenueDetails" xlink:type="extended" id="i2027e45e06004818b7f1a9166037ba4c_RevenuesandTradeReceivablesNetRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_3ad7ce8e-2602-44c1-a8e6-3e74dc88c3c4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_49912b63-da6c-4ad9-ae7f-74f6b5456420" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_3ad7ce8e-2602-44c1-a8e6-3e74dc88c3c4" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_49912b63-da6c-4ad9-ae7f-74f6b5456420" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_15dcc024-f555-4e52-b6e2-a4b644684f98" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_3ad7ce8e-2602-44c1-a8e6-3e74dc88c3c4" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_15dcc024-f555-4e52-b6e2-a4b644684f98" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_04489e5e-b605-4461-993c-3e2003df848f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_15dcc024-f555-4e52-b6e2-a4b644684f98" xlink:to="loc_srt_ProductOrServiceAxis_04489e5e-b605-4461-993c-3e2003df848f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_04489e5e-b605-4461-993c-3e2003df848f_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_04489e5e-b605-4461-993c-3e2003df848f" xlink:to="loc_srt_ProductsAndServicesDomain_04489e5e-b605-4461-993c-3e2003df848f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_21585c42-b8ec-410f-94c2-99615271db7d" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_04489e5e-b605-4461-993c-3e2003df848f" xlink:to="loc_srt_ProductsAndServicesDomain_21585c42-b8ec-410f-94c2-99615271db7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ManufactureAndSupplyRevenueMember_8100ad9a-931b-4ee5-ac1e-fc2116bc37b4" xlink:href="aqst-20230630.xsd#aqst_ManufactureAndSupplyRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_21585c42-b8ec-410f-94c2-99615271db7d" xlink:to="loc_aqst_ManufactureAndSupplyRevenueMember_8100ad9a-931b-4ee5-ac1e-fc2116bc37b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAndRoyaltyRevenueMember_d834b274-0e14-4406-b39c-4e9c80c31c67" xlink:href="aqst-20230630.xsd#aqst_LicenseAndRoyaltyRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_21585c42-b8ec-410f-94c2-99615271db7d" xlink:to="loc_aqst_LicenseAndRoyaltyRevenueMember_d834b274-0e14-4406-b39c-4e9c80c31c67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_CoDevelopmentAndResearchFeesMember_c827bce8-5eb0-4bc7-b9a9-04e3da63d29c" xlink:href="aqst-20230630.xsd#aqst_CoDevelopmentAndResearchFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_21585c42-b8ec-410f-94c2-99615271db7d" xlink:to="loc_aqst_CoDevelopmentAndResearchFeesMember_c827bce8-5eb0-4bc7-b9a9-04e3da63d29c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ProprietaryProductSalesMember_9af28039-5e04-48d0-af5f-e55ce666deae" xlink:href="aqst-20230630.xsd#aqst_ProprietaryProductSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_21585c42-b8ec-410f-94c2-99615271db7d" xlink:to="loc_aqst_ProprietaryProductSalesMember_9af28039-5e04-48d0-af5f-e55ce666deae" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/RevenuesandTradeReceivablesNetDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#RevenuesandTradeReceivablesNetDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/RevenuesandTradeReceivablesNetDisaggregationofRevenueDetails" xlink:type="extended" id="i7f685552567644409aa1aa32876c5e86_RevenuesandTradeReceivablesNetDisaggregationofRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_36433062-e24d-40f8-8e00-865c74ff7ad8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicAreasRevenuesFromExternalCustomersAbstract_2b8318b7-5f01-4caf-b905-42c0e0e5a650" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeographicAreasRevenuesFromExternalCustomersAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_36433062-e24d-40f8-8e00-865c74ff7ad8" xlink:to="loc_us-gaap_GeographicAreasRevenuesFromExternalCustomersAbstract_2b8318b7-5f01-4caf-b905-42c0e0e5a650" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_dbd07a1d-7e6e-439d-8ce8-8c542991ff64" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GeographicAreasRevenuesFromExternalCustomersAbstract_2b8318b7-5f01-4caf-b905-42c0e0e5a650" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_dbd07a1d-7e6e-439d-8ce8-8c542991ff64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_8c8b2ae7-7d49-45e4-849f-9fb7e980f2dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_36433062-e24d-40f8-8e00-865c74ff7ad8" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_8c8b2ae7-7d49-45e4-849f-9fb7e980f2dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_25ac3811-eff4-48cf-9489-d3a1ee6db6dc" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_8c8b2ae7-7d49-45e4-849f-9fb7e980f2dc" xlink:to="loc_srt_StatementGeographicalAxis_25ac3811-eff4-48cf-9489-d3a1ee6db6dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_25ac3811-eff4-48cf-9489-d3a1ee6db6dc_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_25ac3811-eff4-48cf-9489-d3a1ee6db6dc" xlink:to="loc_srt_SegmentGeographicalDomain_25ac3811-eff4-48cf-9489-d3a1ee6db6dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_058c81e8-908a-4f55-9dcc-67272e2b3dbd" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_25ac3811-eff4-48cf-9489-d3a1ee6db6dc" xlink:to="loc_srt_SegmentGeographicalDomain_058c81e8-908a-4f55-9dcc-67272e2b3dbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_15a12089-6c07-47f5-9537-64b9fd9f7822" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_058c81e8-908a-4f55-9dcc-67272e2b3dbd" xlink:to="loc_country_US_15a12089-6c07-47f5-9537-64b9fd9f7822" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_4dd1a213-8761-4953-bd6b-b4b9ad6d8b2e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_058c81e8-908a-4f55-9dcc-67272e2b3dbd" xlink:to="loc_us-gaap_NonUsMember_4dd1a213-8761-4953-bd6b-b4b9ad6d8b2e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/MaterialAgreementsDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#MaterialAgreementsDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/MaterialAgreementsDetails" xlink:type="extended" id="id85e76e2035f48c8ac1b94313eb28e2b_MaterialAgreementsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAgreementTerm_01950f61-2b22-40ec-bebc-1e1d3396bf95" xlink:href="aqst-20230630.xsd#aqst_LicenseAgreementTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_LicenseAgreementTerm_01950f61-2b22-40ec-bebc-1e1d3396bf95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AutomaticRenewalPeriodOfAgreement_5d92e2ea-0d37-474a-b2c5-6eaad5a1bf61" xlink:href="aqst-20230630.xsd#aqst_AutomaticRenewalPeriodOfAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_AutomaticRenewalPeriodOfAgreement_5d92e2ea-0d37-474a-b2c5-6eaad5a1bf61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_28e16361-e2c9-4c6b-89f6-6a2413f59ed7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_us-gaap_Revenues_28e16361-e2c9-4c6b-89f6-6a2413f59ed7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ProceedsFromSaleOfFutureRevenuesNet_f9caa647-7fe9-4728-a3c5-42447541e079" xlink:href="aqst-20230630.xsd#aqst_ProceedsFromSaleOfFutureRevenuesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_ProceedsFromSaleOfFutureRevenuesNet_f9caa647-7fe9-4728-a3c5-42447541e079" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ContingentMonetizationAgreementMilestonePayment_52299cd5-eaed-42d1-bfdb-4afa2ba8d9e5" xlink:href="aqst-20230630.xsd#aqst_ContingentMonetizationAgreementMilestonePayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_ContingentMonetizationAgreementMilestonePayment_52299cd5-eaed-42d1-bfdb-4afa2ba8d9e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLoss_db7a6321-490f-4beb-82b0-f3f2bdf2f0bb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLoss_db7a6321-490f-4beb-82b0-f3f2bdf2f0bb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ProRataPortionOfTargetBonus_35bf8cf3-8c26-461f-8ffe-6691ef38d268" xlink:href="aqst-20230630.xsd#aqst_ProRataPortionOfTargetBonus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_ProRataPortionOfTargetBonus_35bf8cf3-8c26-461f-8ffe-6691ef38d268" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_CashPaymentRepresenting90DaysOfBasePay_51143965-5e49-4f60-a59a-b62adc5eccf3" xlink:href="aqst-20230630.xsd#aqst_CashPaymentRepresenting90DaysOfBasePay"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_CashPaymentRepresenting90DaysOfBasePay_51143965-5e49-4f60-a59a-b62adc5eccf3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_DaysOfBasePay_020be73c-bf25-477f-9e64-8f00af06ea16" xlink:href="aqst-20230630.xsd#aqst_DaysOfBasePay"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_DaysOfBasePay_020be73c-bf25-477f-9e64-8f00af06ea16" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_f6c8824b-b55e-4fb7-8957-7ddeef5a5d67" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_us-gaap_SeveranceCosts1_f6c8824b-b55e-4fb7-8957-7ddeef5a5d67" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NumberOfInstallments_f28aabe6-dec9-471e-bcc4-bb576c949590" xlink:href="aqst-20230630.xsd#aqst_NumberOfInstallments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_NumberOfInstallments_f28aabe6-dec9-471e-bcc4-bb576c949590" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SeverancePeriod_8d9a49ea-ebab-4877-bf40-115fe72d8ed8" xlink:href="aqst-20230630.xsd#aqst_SeverancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_SeverancePeriod_8d9a49ea-ebab-4877-bf40-115fe72d8ed8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_CoverageDuration_64d5b01f-e019-4bd1-9c4c-d437ae4bcb0b" xlink:href="aqst-20230630.xsd#aqst_CoverageDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_CoverageDuration_64d5b01f-e019-4bd1-9c4c-d437ae4bcb0b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ConsultingFee_de358d60-59e3-4a5f-86ce-9dd95b78b150" xlink:href="aqst-20230630.xsd#aqst_ConsultingFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_aqst_ConsultingFee_de358d60-59e3-4a5f-86ce-9dd95b78b150" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromCollaborators_23f7a413-856e-49f8-9d5e-2cfa4507b8b7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromCollaborators"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_us-gaap_ProceedsFromCollaborators_23f7a413-856e-49f8-9d5e-2cfa4507b8b7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ac28a995-e3fb-45b5-9350-c79ca7eb6298" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ac28a995-e3fb-45b5-9350-c79ca7eb6298" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_c94e42e8-0d95-4426-91ef-41d2ef9c11eb" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_bba2b48f-a3a6-4b73-8138-864c6a71c6cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:to="loc_us-gaap_TypeOfArrangementAxis_bba2b48f-a3a6-4b73-8138-864c6a71c6cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_bba2b48f-a3a6-4b73-8138-864c6a71c6cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_bba2b48f-a3a6-4b73-8138-864c6a71c6cc" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_bba2b48f-a3a6-4b73-8138-864c6a71c6cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_bba2b48f-a3a6-4b73-8138-864c6a71c6cc" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_CommercialExploitationAgreementWithIndiviorMember_e1ee878e-bceb-4546-828e-2a2fba665f0c" xlink:href="aqst-20230630.xsd#aqst_CommercialExploitationAgreementWithIndiviorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_CommercialExploitationAgreementWithIndiviorMember_e1ee878e-bceb-4546-828e-2a2fba665f0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SupplementalAgreementWithIndiviorMember_bc2502dc-3267-4e07-b256-d4693c253d0e" xlink:href="aqst-20230630.xsd#aqst_SupplementalAgreementWithIndiviorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_SupplementalAgreementWithIndiviorMember_bc2502dc-3267-4e07-b256-d4693c253d0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_d66cc8b8-d632-4890-ad1f-812ba01c4300" xlink:href="aqst-20230630.xsd#aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_d66cc8b8-d632-4890-ad1f-812ba01c4300" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncUpfrontMember_76e50357-7fa2-4446-9972-b16c6f1b7cc4" xlink:href="aqst-20230630.xsd#aqst_LicenseAgreementWithSunovionPharmaceuticalsIncUpfrontMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_d66cc8b8-d632-4890-ad1f-812ba01c4300" xlink:to="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncUpfrontMember_76e50357-7fa2-4446-9972-b16c6f1b7cc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMilestonesMember_d029b5bf-2c04-4159-913b-337600b4a64a" xlink:href="aqst-20230630.xsd#aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_d66cc8b8-d632-4890-ad1f-812ba01c4300" xlink:to="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMilestonesMember_d029b5bf-2c04-4159-913b-337600b4a64a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_MarathonPangolinRoyaltyLLCMember_bf951ef5-3c45-405c-b9bb-033468d5a19c" xlink:href="aqst-20230630.xsd#aqst_MarathonPangolinRoyaltyLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_MarathonPangolinRoyaltyLLCMember_bf951ef5-3c45-405c-b9bb-033468d5a19c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_HaiscoPharmaceuticalGroupCoLtdUpfrontPaymentMember_348d5dc9-1e49-4a79-afb7-5b7354b28376" xlink:href="aqst-20230630.xsd#aqst_HaiscoPharmaceuticalGroupCoLtdUpfrontPaymentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_HaiscoPharmaceuticalGroupCoLtdUpfrontPaymentMember_348d5dc9-1e49-4a79-afb7-5b7354b28376" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AtnahsPharmaUKLimitedMember_880f8b1c-fa89-4a74-ae7f-27c7c7576327" xlink:href="aqst-20230630.xsd#aqst_AtnahsPharmaUKLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_AtnahsPharmaUKLimitedMember_880f8b1c-fa89-4a74-ae7f-27c7c7576327" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AtnahsPharmaUKLimitedAmendedAgreementMember_2acb6ea9-bc0b-4eb9-9e91-e0e8329525be" xlink:href="aqst-20230630.xsd#aqst_AtnahsPharmaUKLimitedAmendedAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_AtnahsPharmaUKLimitedAmendedAgreementMember_2acb6ea9-bc0b-4eb9-9e91-e0e8329525be" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseSupplyAgreementMember_d3afed93-2e37-4404-ace5-32e3cce2a5b6" xlink:href="aqst-20230630.xsd#aqst_LicenseSupplyAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ae17f64e-edec-4216-a4c7-f294863dbf79" xlink:to="loc_aqst_LicenseSupplyAgreementMember_d3afed93-2e37-4404-ace5-32e3cce2a5b6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b132a30f-6edc-4506-bc13-41be9a19a084" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:to="loc_srt_RangeAxis_b132a30f-6edc-4506-bc13-41be9a19a084" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b132a30f-6edc-4506-bc13-41be9a19a084_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b132a30f-6edc-4506-bc13-41be9a19a084" xlink:to="loc_srt_RangeMember_b132a30f-6edc-4506-bc13-41be9a19a084_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a2a5a8f5-c45e-4306-84e7-addb0d2cce42" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b132a30f-6edc-4506-bc13-41be9a19a084" xlink:to="loc_srt_RangeMember_a2a5a8f5-c45e-4306-84e7-addb0d2cce42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_19799d72-9f4c-425d-8755-7ee86b983301" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_a2a5a8f5-c45e-4306-84e7-addb0d2cce42" xlink:to="loc_srt_MinimumMember_19799d72-9f4c-425d-8755-7ee86b983301" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_d8982005-d53f-45e5-85e0-5fcfb3924fb0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_a2a5a8f5-c45e-4306-84e7-addb0d2cce42" xlink:to="loc_srt_MaximumMember_d8982005-d53f-45e5-85e0-5fcfb3924fb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_72d9fe25-225d-46e8-a53c-00c9759cb738" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:to="loc_srt_ProductOrServiceAxis_72d9fe25-225d-46e8-a53c-00c9759cb738" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_72d9fe25-225d-46e8-a53c-00c9759cb738_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_72d9fe25-225d-46e8-a53c-00c9759cb738" xlink:to="loc_srt_ProductsAndServicesDomain_72d9fe25-225d-46e8-a53c-00c9759cb738_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_342ed785-9847-49d1-bf0e-49610208881e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_72d9fe25-225d-46e8-a53c-00c9759cb738" xlink:to="loc_srt_ProductsAndServicesDomain_342ed785-9847-49d1-bf0e-49610208881e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAndRoyaltyRevenueMember_12f34f73-ed30-4de9-bff2-4b00df366dda" xlink:href="aqst-20230630.xsd#aqst_LicenseAndRoyaltyRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_342ed785-9847-49d1-bf0e-49610208881e" xlink:to="loc_aqst_LicenseAndRoyaltyRevenueMember_12f34f73-ed30-4de9-bff2-4b00df366dda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_f3e02a4a-24f3-455a-bea7-ea160bc76013" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:to="loc_us-gaap_CreditFacilityAxis_f3e02a4a-24f3-455a-bea7-ea160bc76013" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f3e02a4a-24f3-455a-bea7-ea160bc76013_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_f3e02a4a-24f3-455a-bea7-ea160bc76013" xlink:to="loc_us-gaap_CreditFacilityDomain_f3e02a4a-24f3-455a-bea7-ea160bc76013_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_88a03ff0-f28d-4431-98a4-dadd961158e6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_f3e02a4a-24f3-455a-bea7-ea160bc76013" xlink:to="loc_us-gaap_CreditFacilityDomain_88a03ff0-f28d-4431-98a4-dadd961158e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_MonetizationAgreementMember_9d781e2d-7cec-4657-b75c-2298173d758e" xlink:href="aqst-20230630.xsd#aqst_MonetizationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_88a03ff0-f28d-4431-98a4-dadd961158e6" xlink:to="loc_aqst_MonetizationAgreementMember_9d781e2d-7cec-4657-b75c-2298173d758e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseSupplyAgreementMember_7d292d46-68d2-4b96-b9b6-08064461cd62" xlink:href="aqst-20230630.xsd#aqst_LicenseSupplyAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_88a03ff0-f28d-4431-98a4-dadd961158e6" xlink:to="loc_aqst_LicenseSupplyAgreementMember_7d292d46-68d2-4b96-b9b6-08064461cd62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AtnahsPharmaUKLimitedMember_9f247e28-d00a-4868-810d-8f27807ab465" xlink:href="aqst-20230630.xsd#aqst_AtnahsPharmaUKLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_88a03ff0-f28d-4431-98a4-dadd961158e6" xlink:to="loc_aqst_AtnahsPharmaUKLimitedMember_9f247e28-d00a-4868-810d-8f27807ab465" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_DurationOfPaymentAxis_20f6ffe1-8b30-45a8-981f-176e115ca955" xlink:href="aqst-20230630.xsd#aqst_DurationOfPaymentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:to="loc_aqst_DurationOfPaymentAxis_20f6ffe1-8b30-45a8-981f-176e115ca955" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_DurationOfPaymentDomain_20f6ffe1-8b30-45a8-981f-176e115ca955_default" xlink:href="aqst-20230630.xsd#aqst_DurationOfPaymentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aqst_DurationOfPaymentAxis_20f6ffe1-8b30-45a8-981f-176e115ca955" xlink:to="loc_aqst_DurationOfPaymentDomain_20f6ffe1-8b30-45a8-981f-176e115ca955_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_DurationOfPaymentDomain_d695e30e-d50c-4917-82f8-d3907cbcbfdf" xlink:href="aqst-20230630.xsd#aqst_DurationOfPaymentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aqst_DurationOfPaymentAxis_20f6ffe1-8b30-45a8-981f-176e115ca955" xlink:to="loc_aqst_DurationOfPaymentDomain_d695e30e-d50c-4917-82f8-d3907cbcbfdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_FirstSevenMonthsMember_a1b53d9f-8dc0-4e80-9ab9-200019dbc85c" xlink:href="aqst-20230630.xsd#aqst_FirstSevenMonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_DurationOfPaymentDomain_d695e30e-d50c-4917-82f8-d3907cbcbfdf" xlink:to="loc_aqst_FirstSevenMonthsMember_a1b53d9f-8dc0-4e80-9ab9-200019dbc85c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_EighthMonthMember_f1dd8140-66a8-4446-bde2-44810b57ff95" xlink:href="aqst-20230630.xsd#aqst_EighthMonthMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_DurationOfPaymentDomain_d695e30e-d50c-4917-82f8-d3907cbcbfdf" xlink:to="loc_aqst_EighthMonthMember_f1dd8140-66a8-4446-bde2-44810b57ff95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NinthThroughEighteenthMonthMember_31fe7cc4-64eb-4491-9c0c-5c14f6395691" xlink:href="aqst-20230630.xsd#aqst_NinthThroughEighteenthMonthMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_DurationOfPaymentDomain_d695e30e-d50c-4917-82f8-d3907cbcbfdf" xlink:to="loc_aqst_NinthThroughEighteenthMonthMember_31fe7cc4-64eb-4491-9c0c-5c14f6395691" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_e1941b0d-43fc-44a2-b8fe-134fcdad5173" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c9fba309-1bd7-4c8b-998e-da8df57caeaa" xlink:to="loc_srt_CounterpartyNameAxis_e1941b0d-43fc-44a2-b8fe-134fcdad5173" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_e1941b0d-43fc-44a2-b8fe-134fcdad5173_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_e1941b0d-43fc-44a2-b8fe-134fcdad5173" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_e1941b0d-43fc-44a2-b8fe-134fcdad5173_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_95f74bd4-d599-4157-a0ee-1cf726f7a417" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_e1941b0d-43fc-44a2-b8fe-134fcdad5173" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_95f74bd4-d599-4157-a0ee-1cf726f7a417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AssertioHoldingsIncMember_3e113e56-0205-47ff-b13e-f9163780e398" xlink:href="aqst-20230630.xsd#aqst_AssertioHoldingsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_95f74bd4-d599-4157-a0ee-1cf726f7a417" xlink:to="loc_aqst_AssertioHoldingsIncMember_3e113e56-0205-47ff-b13e-f9163780e398" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/FinancialInstrumentsFairValueMeasurementsDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#FinancialInstrumentsFairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/FinancialInstrumentsFairValueMeasurementsDetails" xlink:type="extended" id="ieed6167a3a954a9b80d5e26031933bfb_FinancialInstrumentsFairValueMeasurementsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_1bdec476-912e-40dc-8592-5439dca1375c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_WarrantsLiabilityAbstract_e9fbfdd7-0e19-4a4b-b37c-b04a58bffc15" xlink:href="aqst-20230630.xsd#aqst_WarrantsLiabilityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_1bdec476-912e-40dc-8592-5439dca1375c" xlink:to="loc_aqst_WarrantsLiabilityAbstract_e9fbfdd7-0e19-4a4b-b37c-b04a58bffc15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_507d4267-0452-412b-bed4-31752b5a6c1b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_WarrantsLiabilityAbstract_e9fbfdd7-0e19-4a4b-b37c-b04a58bffc15" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_507d4267-0452-412b-bed4-31752b5a6c1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SharesOfCommonStockEntitledToPurchasersByPreFundedWarrants_330e1754-3c6d-40bd-8a5d-897b43ea3fc7" xlink:href="aqst-20230630.xsd#aqst_SharesOfCommonStockEntitledToPurchasersByPreFundedWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_WarrantsLiabilityAbstract_e9fbfdd7-0e19-4a4b-b37c-b04a58bffc15" xlink:to="loc_aqst_SharesOfCommonStockEntitledToPurchasersByPreFundedWarrants_330e1754-3c6d-40bd-8a5d-897b43ea3fc7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SharesOfCommonStockToBePurchasedByCommonStockWarrants_e3734883-06c1-4740-9319-38f997560c71" xlink:href="aqst-20230630.xsd#aqst_SharesOfCommonStockToBePurchasedByCommonStockWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_WarrantsLiabilityAbstract_e9fbfdd7-0e19-4a4b-b37c-b04a58bffc15" xlink:to="loc_aqst_SharesOfCommonStockToBePurchasedByCommonStockWarrants_e3734883-06c1-4740-9319-38f997560c71" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_5870aaff-5b58-4bbf-b8f2-a2761ee96f5e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_1bdec476-912e-40dc-8592-5439dca1375c" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_5870aaff-5b58-4bbf-b8f2-a2761ee96f5e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_2579a4f5-b670-465b-826a-f5285d738e44" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_5870aaff-5b58-4bbf-b8f2-a2761ee96f5e" xlink:to="loc_us-gaap_DebtInstrumentAxis_2579a4f5-b670-465b-826a-f5285d738e44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2579a4f5-b670-465b-826a-f5285d738e44_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_2579a4f5-b670-465b-826a-f5285d738e44" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2579a4f5-b670-465b-826a-f5285d738e44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_00ed9201-83fb-401d-b5b8-490679170667" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_2579a4f5-b670-465b-826a-f5285d738e44" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_00ed9201-83fb-401d-b5b8-490679170667" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_492907f5-d916-4777-b238-1562f9720d70" xlink:href="aqst-20230630.xsd#aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_00ed9201-83fb-401d-b5b8-490679170667" xlink:to="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_492907f5-d916-4777-b238-1562f9720d70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_d0d624d1-d768-4a2c-8e5a-089f69b253f0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_5870aaff-5b58-4bbf-b8f2-a2761ee96f5e" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_d0d624d1-d768-4a2c-8e5a-089f69b253f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_d0d624d1-d768-4a2c-8e5a-089f69b253f0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_d0d624d1-d768-4a2c-8e5a-089f69b253f0" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_d0d624d1-d768-4a2c-8e5a-089f69b253f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5856ec7c-cb81-45c4-b94f-20e69828c752" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_d0d624d1-d768-4a2c-8e5a-089f69b253f0" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5856ec7c-cb81-45c4-b94f-20e69828c752" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SecuritiesPurchaseAgreementMember_6475602a-7a03-4250-be2d-50563e38b617" xlink:href="aqst-20230630.xsd#aqst_SecuritiesPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5856ec7c-cb81-45c4-b94f-20e69828c752" xlink:to="loc_aqst_SecuritiesPurchaseAgreementMember_6475602a-7a03-4250-be2d-50563e38b617" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/PropertyandEquipmentNetSummaryofPropertyandEquipmentDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#PropertyandEquipmentNetSummaryofPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/PropertyandEquipmentNetSummaryofPropertyandEquipmentDetails" xlink:type="extended" id="ibff815bcb0b5486690bfb0b3c25529d7_PropertyandEquipmentNetSummaryofPropertyandEquipmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_94fc7a58-6b1f-4481-a091-e3793def47d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_6155b51f-9067-42dc-a8a2-226c1bdb633b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_94fc7a58-6b1f-4481-a091-e3793def47d8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_6155b51f-9067-42dc-a8a2-226c1bdb633b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_75a5216b-e0e6-459e-9f7f-3fedb66e6643" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_94fc7a58-6b1f-4481-a091-e3793def47d8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_75a5216b-e0e6-459e-9f7f-3fedb66e6643" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_4a689def-bbba-4aa3-b108-1c86cb6349dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_94fc7a58-6b1f-4481-a091-e3793def47d8" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_4a689def-bbba-4aa3-b108-1c86cb6349dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_73555e31-55b9-4822-8f40-b779c4db35f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_94fc7a58-6b1f-4481-a091-e3793def47d8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_73555e31-55b9-4822-8f40-b779c4db35f3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_5ead48bb-2dd6-4e0d-a4df-867a91dd09da" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_94fc7a58-6b1f-4481-a091-e3793def47d8" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_5ead48bb-2dd6-4e0d-a4df-867a91dd09da" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_37806d91-9167-4fbf-a8f1-84d5386d72b0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_5ead48bb-2dd6-4e0d-a4df-867a91dd09da" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_37806d91-9167-4fbf-a8f1-84d5386d72b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_37806d91-9167-4fbf-a8f1-84d5386d72b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_37806d91-9167-4fbf-a8f1-84d5386d72b0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_37806d91-9167-4fbf-a8f1-84d5386d72b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ff0040da-6260-4084-8741-e7488500838c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_37806d91-9167-4fbf-a8f1-84d5386d72b0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ff0040da-6260-4084-8741-e7488500838c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_674671b6-f50e-4feb-b8ef-c5e1b5926bab" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ff0040da-6260-4084-8741-e7488500838c" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_674671b6-f50e-4feb-b8ef-c5e1b5926bab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_e5f5ab66-1619-42a4-aa29-32285852c03c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ff0040da-6260-4084-8741-e7488500838c" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_e5f5ab66-1619-42a4-aa29-32285852c03c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_1852994c-0ffb-4d71-9a46-e84622cb5638" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ff0040da-6260-4084-8741-e7488500838c" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_1852994c-0ffb-4d71-9a46-e84622cb5638" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ComputerNetworkEquipmentAndSoftwareMember_c73df95b-c141-4691-9939-97a8b8808edb" xlink:href="aqst-20230630.xsd#aqst_ComputerNetworkEquipmentAndSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ff0040da-6260-4084-8741-e7488500838c" xlink:to="loc_aqst_ComputerNetworkEquipmentAndSoftwareMember_c73df95b-c141-4691-9939-97a8b8808edb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_e142b14a-1489-4d35-8ab8-c372c54cd0ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ff0040da-6260-4084-8741-e7488500838c" xlink:to="loc_us-gaap_ConstructionInProgressMember_e142b14a-1489-4d35-8ab8-c372c54cd0ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_29d5513f-cc37-47fd-8af9-a119fd8efdfa" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_5ead48bb-2dd6-4e0d-a4df-867a91dd09da" xlink:to="loc_srt_RangeAxis_29d5513f-cc37-47fd-8af9-a119fd8efdfa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_29d5513f-cc37-47fd-8af9-a119fd8efdfa_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_29d5513f-cc37-47fd-8af9-a119fd8efdfa" xlink:to="loc_srt_RangeMember_29d5513f-cc37-47fd-8af9-a119fd8efdfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1684ce9a-cacd-4048-9140-1dfd2d13125b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_29d5513f-cc37-47fd-8af9-a119fd8efdfa" xlink:to="loc_srt_RangeMember_1684ce9a-cacd-4048-9140-1dfd2d13125b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_7a8e2fa8-1196-4bfb-aa66-522539e68b4b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1684ce9a-cacd-4048-9140-1dfd2d13125b" xlink:to="loc_srt_MinimumMember_7a8e2fa8-1196-4bfb-aa66-522539e68b4b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_54bbf57d-ffde-4d8b-acfd-76e0c36a5e30" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1684ce9a-cacd-4048-9140-1dfd2d13125b" xlink:to="loc_srt_MaximumMember_54bbf57d-ffde-4d8b-acfd-76e0c36a5e30" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/RightofUseAssetsandLeaseObligationsNarrativeDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#RightofUseAssetsandLeaseObligationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/RightofUseAssetsandLeaseObligationsNarrativeDetails" xlink:type="extended" id="ic69d5ade90dd4df1949237b0aa61f9ba_RightofUseAssetsandLeaseObligationsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_9c4ad865-3243-465f-819f-f294363024b9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NumberOfOperatingLeases_d3835ca3-7cd6-4b6e-9726-c495cd6c3112" xlink:href="aqst-20230630.xsd#aqst_NumberOfOperatingLeases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_9c4ad865-3243-465f-819f-f294363024b9" xlink:to="loc_aqst_NumberOfOperatingLeases_d3835ca3-7cd6-4b6e-9726-c495cd6c3112" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_68ee4284-1406-4bbe-bbc0-2045ab3afcff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_9c4ad865-3243-465f-819f-f294363024b9" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_68ee4284-1406-4bbe-bbc0-2045ab3afcff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseCost_b65a0ffa-4154-4d28-9168-d34029919b37" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_9c4ad865-3243-465f-819f-f294363024b9" xlink:to="loc_us-gaap_OperatingLeaseCost_b65a0ffa-4154-4d28-9168-d34029919b37" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableLeaseCost_af97e2df-f5a5-4d86-8885-146a054509da" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_9c4ad865-3243-465f-819f-f294363024b9" xlink:to="loc_us-gaap_VariableLeaseCost_af97e2df-f5a5-4d86-8885-146a054509da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseDiscountRate_b1e13289-d983-4b4a-993e-ead89617f0e1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LesseeOperatingLeaseDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_9c4ad865-3243-465f-819f-f294363024b9" xlink:to="loc_us-gaap_LesseeOperatingLeaseDiscountRate_b1e13289-d983-4b4a-993e-ead89617f0e1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_673a4879-95da-441b-9a84-09e00031549a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_9c4ad865-3243-465f-819f-f294363024b9" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_673a4879-95da-441b-9a84-09e00031549a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e2f7b02d-7677-4ce0-846a-47e6549c73ab" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_673a4879-95da-441b-9a84-09e00031549a" xlink:to="loc_srt_RangeAxis_e2f7b02d-7677-4ce0-846a-47e6549c73ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e2f7b02d-7677-4ce0-846a-47e6549c73ab_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e2f7b02d-7677-4ce0-846a-47e6549c73ab" xlink:to="loc_srt_RangeMember_e2f7b02d-7677-4ce0-846a-47e6549c73ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4f5e7c7e-b6df-4b3a-969d-14a791245ab7" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e2f7b02d-7677-4ce0-846a-47e6549c73ab" xlink:to="loc_srt_RangeMember_4f5e7c7e-b6df-4b3a-969d-14a791245ab7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_ce0ce8d5-ef61-4673-86a9-4162c020a7aa" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4f5e7c7e-b6df-4b3a-969d-14a791245ab7" xlink:to="loc_srt_MinimumMember_ce0ce8d5-ef61-4673-86a9-4162c020a7aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a3eebf71-4122-440a-8145-4caab7c149ff" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4f5e7c7e-b6df-4b3a-969d-14a791245ab7" xlink:to="loc_srt_MaximumMember_a3eebf71-4122-440a-8145-4caab7c149ff" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/IntangibleAssetsNetComponentsofIdentifiableIntangibleAssetsDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#IntangibleAssetsNetComponentsofIdentifiableIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/IntangibleAssetsNetComponentsofIdentifiableIntangibleAssetsDetails" xlink:type="extended" id="ic1d73d61ce494db59446ae6961547cde_IntangibleAssetsNetComponentsofIdentifiableIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d8d28b69-ce4d-4e0e-920a-cf16a9597ab3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_d2c53cf5-c997-47cd-9895-2a598658aeb9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d8d28b69-ce4d-4e0e-920a-cf16a9597ab3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_d2c53cf5-c997-47cd-9895-2a598658aeb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_156c6077-8222-4f1f-816f-8f00ce7f3b3a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_d2c53cf5-c997-47cd-9895-2a598658aeb9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_156c6077-8222-4f1f-816f-8f00ce7f3b3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_5252b66e-623a-4cd1-a401-042a772d50b6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_d2c53cf5-c997-47cd-9895-2a598658aeb9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_5252b66e-623a-4cd1-a401-042a772d50b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_a9aa8fc2-dcd8-4f7d-a21f-45ab05c03721" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_d2c53cf5-c997-47cd-9895-2a598658aeb9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_a9aa8fc2-dcd8-4f7d-a21f-45ab05c03721" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_9acb5426-745e-4724-8aa5-7a009c2d5449" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d8d28b69-ce4d-4e0e-920a-cf16a9597ab3" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_9acb5426-745e-4724-8aa5-7a009c2d5449" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e4519127-6c10-4263-bf87-a09c2937ae7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_9acb5426-745e-4724-8aa5-7a009c2d5449" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e4519127-6c10-4263-bf87-a09c2937ae7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e4519127-6c10-4263-bf87-a09c2937ae7c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e4519127-6c10-4263-bf87-a09c2937ae7c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e4519127-6c10-4263-bf87-a09c2937ae7c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_0dfd4d7c-ec1a-47ef-bcdb-1d2293c2e099" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e4519127-6c10-4263-bf87-a09c2937ae7c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_0dfd4d7c-ec1a-47ef-bcdb-1d2293c2e099" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_aaad1c4a-f0a4-4480-840e-5104545fafec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_0dfd4d7c-ec1a-47ef-bcdb-1d2293c2e099" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_aaad1c4a-f0a4-4480-840e-5104545fafec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_3601d9b3-17cb-4bbe-90cb-ff22e26ba256" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_0dfd4d7c-ec1a-47ef-bcdb-1d2293c2e099" xlink:to="loc_us-gaap_PatentsMember_3601d9b3-17cb-4bbe-90cb-ff22e26ba256" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/OtherNoncurrentAssetsNarrativeDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#OtherNoncurrentAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/OtherNoncurrentAssetsNarrativeDetails" xlink:type="extended" id="i1b37e2b49e644a8bbdf3c58d0f83522e_OtherNoncurrentAssetsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_61fd0608-3323-49a0-94af-82436df413ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_7994c5c3-33e3-44e2-9bd7-01de724d0c2d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_61fd0608-3323-49a0-94af-82436df413ea" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_7994c5c3-33e3-44e2-9bd7-01de724d0c2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NumberOfGuaranteedRoyaltyPayments_29ceb0c1-b64d-4292-9b64-a2921a38d747" xlink:href="aqst-20230630.xsd#aqst_NumberOfGuaranteedRoyaltyPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_61fd0608-3323-49a0-94af-82436df413ea" xlink:to="loc_aqst_NumberOfGuaranteedRoyaltyPayments_29ceb0c1-b64d-4292-9b64-a2921a38d747" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_MinimumAnnualRoyaltyReceivable_fc1f9f10-17c9-4fd9-8c5f-0ea58cfbed0e" xlink:href="aqst-20230630.xsd#aqst_MinimumAnnualRoyaltyReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_61fd0608-3323-49a0-94af-82436df413ea" xlink:to="loc_aqst_MinimumAnnualRoyaltyReceivable_fc1f9f10-17c9-4fd9-8c5f-0ea58cfbed0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NumberOfAnnualRoyaltyPaymentsReceivable_ffea1c29-5d05-4108-91f9-40fc43f81f23" xlink:href="aqst-20230630.xsd#aqst_NumberOfAnnualRoyaltyPaymentsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_61fd0608-3323-49a0-94af-82436df413ea" xlink:to="loc_aqst_NumberOfAnnualRoyaltyPaymentsReceivable_ffea1c29-5d05-4108-91f9-40fc43f81f23" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_de9150fd-7340-47b6-89bd-5695f74ca52f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_61fd0608-3323-49a0-94af-82436df413ea" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_de9150fd-7340-47b6-89bd-5695f74ca52f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_385f299e-03c5-42ce-b48b-c46c030ff8a0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_de9150fd-7340-47b6-89bd-5695f74ca52f" xlink:to="loc_srt_ProductOrServiceAxis_385f299e-03c5-42ce-b48b-c46c030ff8a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_385f299e-03c5-42ce-b48b-c46c030ff8a0_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_385f299e-03c5-42ce-b48b-c46c030ff8a0" xlink:to="loc_srt_ProductsAndServicesDomain_385f299e-03c5-42ce-b48b-c46c030ff8a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_81adddbb-a938-48ce-8c6b-6a04c98b3d10" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_385f299e-03c5-42ce-b48b-c46c030ff8a0" xlink:to="loc_srt_ProductsAndServicesDomain_81adddbb-a938-48ce-8c6b-6a04c98b3d10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_a5de289a-9ced-4134-8983-f0835cfe1831" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_81adddbb-a938-48ce-8c6b-6a04c98b3d10" xlink:to="loc_us-gaap_RoyaltyMember_a5de289a-9ced-4134-8983-f0835cfe1831" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_ed138bd5-ec3a-4bd1-99d1-ac775d093d1a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_de9150fd-7340-47b6-89bd-5695f74ca52f" xlink:to="loc_us-gaap_TypeOfArrangementAxis_ed138bd5-ec3a-4bd1-99d1-ac775d093d1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ed138bd5-ec3a-4bd1-99d1-ac775d093d1a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_ed138bd5-ec3a-4bd1-99d1-ac775d093d1a" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ed138bd5-ec3a-4bd1-99d1-ac775d093d1a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_b5acd31d-0454-483e-868e-01e29d83e411" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_ed138bd5-ec3a-4bd1-99d1-ac775d093d1a" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_b5acd31d-0454-483e-868e-01e29d83e411" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_49607b70-4620-489f-ba21-911b2c8c9b5b" xlink:href="aqst-20230630.xsd#aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_b5acd31d-0454-483e-868e-01e29d83e411" xlink:to="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_49607b70-4620-489f-ba21-911b2c8c9b5b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/A125SeniorSecuredNotesandLoansPayable125SeniorSecuredNotesDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#A125SeniorSecuredNotesandLoansPayable125SeniorSecuredNotesDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/A125SeniorSecuredNotesandLoansPayable125SeniorSecuredNotesDetails" xlink:type="extended" id="ieb689450df4243029b81a842117b4516_A125SeniorSecuredNotesandLoansPayable125SeniorSecuredNotesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_0f6f203e-bdf7-4258-b136-2903175f3aac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:href="aqst-20230630.xsd#aqst_SeniorSecuredNotesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0f6f203e-bdf7-4258-b136-2903175f3aac" xlink:to="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_bcef0927-88bc-4f6f-a4bb-fbebaf74c2fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_bcef0927-88bc-4f6f-a4bb-fbebaf74c2fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_374bd09a-6588-4900-9fab-0241d62d54b6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_374bd09a-6588-4900-9fab-0241d62d54b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_9f38b927-1728-474e-810e-2cf7dce779d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_9f38b927-1728-474e-810e-2cf7dce779d0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_2f091e8f-f604-40ab-ad64-18c13dc51071" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_2f091e8f-f604-40ab-ad64-18c13dc51071" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NetProceedsFromIssuanceOfInitialNotesWarrantsAndFirstOfferRights_cfac9858-b257-43dc-8116-cd3409b5f6c3" xlink:href="aqst-20230630.xsd#aqst_NetProceedsFromIssuanceOfInitialNotesWarrantsAndFirstOfferRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_aqst_NetProceedsFromIssuanceOfInitialNotesWarrantsAndFirstOfferRights_cfac9858-b257-43dc-8116-cd3409b5f6c3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfDebt_4415c187-cc27-4bd8-a07a-9a3e7119fa9f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RepaymentsOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_RepaymentsOfDebt_4415c187-cc27-4bd8-a07a-9a3e7119fa9f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_3b6b0eb0-df04-4f28-9f4d-169acb7757fb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_LongTermDebt_3b6b0eb0-df04-4f28-9f4d-169acb7757fb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_5abd84e5-d7c8-46a8-ba59-e6dd0938797c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_5abd84e5-d7c8-46a8-ba59-e6dd0938797c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_PremiumsPaidEarlyRetirementOfDebt_e1894e57-12ad-4eae-8e9b-8fcf956e28b7" xlink:href="aqst-20230630.xsd#aqst_PremiumsPaidEarlyRetirementOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_aqst_PremiumsPaidEarlyRetirementOfDebt_e1894e57-12ad-4eae-8e9b-8fcf956e28b7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfLoanCosts_f842479d-936d-4540-b3d2-5ed78c4aa423" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfLoanCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_PaymentsOfLoanCosts_f842479d-936d-4540-b3d2-5ed78c4aa423" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_ee9f3663-370d-424e-9d14-2e800837c377" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_ee9f3663-370d-424e-9d14-2e800837c377" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_RepurchaseOfferPercentageOfCashProceedsReceived_d5a3fa8a-e7b2-4852-a287-820b9dab555b" xlink:href="aqst-20230630.xsd#aqst_RepurchaseOfferPercentageOfCashProceedsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_aqst_RepurchaseOfferPercentageOfCashProceedsReceived_d5a3fa8a-e7b2-4852-a287-820b9dab555b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_3a729985-8d00-4ebe-bb40-0956255cfe07" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_LongTermDebtFairValue_3a729985-8d00-4ebe-bb40-0956255cfe07" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod_d56a2769-cd9c-4b22-ba29-5744193bdf5f" xlink:href="aqst-20230630.xsd#aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod_d56a2769-cd9c-4b22-ba29-5744193bdf5f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_DebtInstrumentAdditionalBorrowingCapacity_765f9924-a75a-4fd6-8eb2-e7bd1d513414" xlink:href="aqst-20230630.xsd#aqst_DebtInstrumentAdditionalBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_aqst_DebtInstrumentAdditionalBorrowingCapacity_765f9924-a75a-4fd6-8eb2-e7bd1d513414" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_87de81f4-59a0-418c-bf3d-4c87b2de6310" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_87de81f4-59a0-418c-bf3d-4c87b2de6310" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ElectiveRedemptionPercentageOfDebt_9ee5fe1c-4ff7-45a6-bf45-f3898ca7c0ee" xlink:href="aqst-20230630.xsd#aqst_ElectiveRedemptionPercentageOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_aqst_ElectiveRedemptionPercentageOfDebt_9ee5fe1c-4ff7-45a6-bf45-f3898ca7c0ee" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_RedemptionPercentageOfDebtUnderChangeOfControlProvisions_cecff99a-92f2-4ef4-b651-35c2d737aa70" xlink:href="aqst-20230630.xsd#aqst_RedemptionPercentageOfDebtUnderChangeOfControlProvisions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_aqst_RedemptionPercentageOfDebtUnderChangeOfControlProvisions_cecff99a-92f2-4ef4-b651-35c2d737aa70" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtExtinguishmentCosts_62d6a2c7-20e4-4588-a584-8feb2e9edf67" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfDebtExtinguishmentCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_PaymentsOfDebtExtinguishmentCosts_62d6a2c7-20e4-4588-a584-8feb2e9edf67" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_8336e6ff-cefb-42f0-9008-1eb23e5ac44f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_8336e6ff-cefb-42f0-9008-1eb23e5ac44f" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_2455bdb1-7d8c-4183-aa9a-c7343bf49de4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SeniorSecuredNotesAbstract_f80af06b-823e-42cd-9119-4cc4ddb960c5" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_2455bdb1-7d8c-4183-aa9a-c7343bf49de4" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_2bfa1cf4-86cc-4c8b-988f-dae73c9dbdc8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0f6f203e-bdf7-4258-b136-2903175f3aac" xlink:to="loc_us-gaap_DebtInstrumentTable_2bfa1cf4-86cc-4c8b-988f-dae73c9dbdc8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_8e1e1c30-4ada-4129-bd8b-0053596c2d80" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2bfa1cf4-86cc-4c8b-988f-dae73c9dbdc8" xlink:to="loc_us-gaap_DebtInstrumentAxis_8e1e1c30-4ada-4129-bd8b-0053596c2d80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_8e1e1c30-4ada-4129-bd8b-0053596c2d80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_8e1e1c30-4ada-4129-bd8b-0053596c2d80" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_8e1e1c30-4ada-4129-bd8b-0053596c2d80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4f65ab1e-db7c-49e8-bda1-04d5e15441c4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_8e1e1c30-4ada-4129-bd8b-0053596c2d80" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4f65ab1e-db7c-49e8-bda1-04d5e15441c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_cbb556bb-3e57-4e9f-b974-6e3ccfcb51f4" xlink:href="aqst-20230630.xsd#aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4f65ab1e-db7c-49e8-bda1-04d5e15441c4" xlink:to="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_cbb556bb-3e57-4e9f-b974-6e3ccfcb51f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_FirstAdditionalOfferingMember_519b2f03-c41a-4732-a9b0-7943f13c5472" xlink:href="aqst-20230630.xsd#aqst_FirstAdditionalOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_cbb556bb-3e57-4e9f-b974-6e3ccfcb51f4" xlink:to="loc_aqst_FirstAdditionalOfferingMember_519b2f03-c41a-4732-a9b0-7943f13c5472" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SecondAdditionalOfferingMember_cf091739-1da8-4ec5-84d2-75e14c312f8c" xlink:href="aqst-20230630.xsd#aqst_SecondAdditionalOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_cbb556bb-3e57-4e9f-b974-6e3ccfcb51f4" xlink:to="loc_aqst_SecondAdditionalOfferingMember_cf091739-1da8-4ec5-84d2-75e14c312f8c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_4440932d-d22f-4cf7-98b7-31d4df436cc2" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2bfa1cf4-86cc-4c8b-988f-dae73c9dbdc8" xlink:to="loc_srt_RangeAxis_4440932d-d22f-4cf7-98b7-31d4df436cc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4440932d-d22f-4cf7-98b7-31d4df436cc2_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_4440932d-d22f-4cf7-98b7-31d4df436cc2" xlink:to="loc_srt_RangeMember_4440932d-d22f-4cf7-98b7-31d4df436cc2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fa29eece-c2c9-41d5-8d12-8b950159268d" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_4440932d-d22f-4cf7-98b7-31d4df436cc2" xlink:to="loc_srt_RangeMember_fa29eece-c2c9-41d5-8d12-8b950159268d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_4d9876a2-bf87-4c31-8cbe-3b68fcf00e38" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fa29eece-c2c9-41d5-8d12-8b950159268d" xlink:to="loc_srt_MinimumMember_4d9876a2-bf87-4c31-8cbe-3b68fcf00e38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a7464fb6-0ec7-41a6-be8c-ee11ca0fccaa" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fa29eece-c2c9-41d5-8d12-8b950159268d" xlink:to="loc_srt_MaximumMember_a7464fb6-0ec7-41a6-be8c-ee11ca0fccaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a571f914-b88e-4489-9211-074345c67242" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2bfa1cf4-86cc-4c8b-988f-dae73c9dbdc8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a571f914-b88e-4489-9211-074345c67242" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a571f914-b88e-4489-9211-074345c67242_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a571f914-b88e-4489-9211-074345c67242" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a571f914-b88e-4489-9211-074345c67242_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ad6623d6-dbf1-48c7-a201-fd4e5dd1a6cd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a571f914-b88e-4489-9211-074345c67242" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ad6623d6-dbf1-48c7-a201-fd4e5dd1a6cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_c565f7c1-f0ef-4584-bf0f-98c339be0fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ad6623d6-dbf1-48c7-a201-fd4e5dd1a6cd" xlink:to="loc_us-gaap_SeniorNotesMember_c565f7c1-f0ef-4584-bf0f-98c339be0fd6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_05f8a0e1-2445-4759-9897-f63c182897cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2bfa1cf4-86cc-4c8b-988f-dae73c9dbdc8" xlink:to="loc_us-gaap_TypeOfArrangementAxis_05f8a0e1-2445-4759-9897-f63c182897cc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_05f8a0e1-2445-4759-9897-f63c182897cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_05f8a0e1-2445-4759-9897-f63c182897cc" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_05f8a0e1-2445-4759-9897-f63c182897cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ce217d31-ef5d-4550-8b38-12242908d3ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_05f8a0e1-2445-4759-9897-f63c182897cc" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ce217d31-ef5d-4550-8b38-12242908d3ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_MarathonPangolinRoyaltyLLCMember_b19ab072-0153-4fab-b3c0-1c046b55610d" xlink:href="aqst-20230630.xsd#aqst_MarathonPangolinRoyaltyLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ce217d31-ef5d-4550-8b38-12242908d3ae" xlink:to="loc_aqst_MarathonPangolinRoyaltyLLCMember_b19ab072-0153-4fab-b3c0-1c046b55610d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_4353d880-4436-4a67-abd3-03eaf562c3f1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2bfa1cf4-86cc-4c8b-988f-dae73c9dbdc8" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_4353d880-4436-4a67-abd3-03eaf562c3f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_4353d880-4436-4a67-abd3-03eaf562c3f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_4353d880-4436-4a67-abd3-03eaf562c3f1" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_4353d880-4436-4a67-abd3-03eaf562c3f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_5ca5f067-a2cf-45d7-b9df-e0d0c0e96e41" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_4353d880-4436-4a67-abd3-03eaf562c3f1" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_5ca5f067-a2cf-45d7-b9df-e0d0c0e96e41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PutOptionMember_30e79db6-804f-4245-83d8-f850743d9cb6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PutOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_5ca5f067-a2cf-45d7-b9df-e0d0c0e96e41" xlink:to="loc_us-gaap_PutOptionMember_30e79db6-804f-4245-83d8-f850743d9cb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1ad016ac-54aa-45d8-bc0a-5829c936e553" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1ad016ac-54aa-45d8-bc0a-5829c936e553_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_390bc507-aa80-4281-bf5e-1d7ccc01ede8" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a270873f-df03-4ad0-b0bc-11a55afb7cff" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/WarrantsDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#WarrantsDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/WarrantsDetails" xlink:type="extended" id="i2dd0bd4cfad74d3aba4411a121769fa8_WarrantsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_42be4f93-4451-4d13-93f7-273378fdd81d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_42be4f93-4451-4d13-93f7-273378fdd81d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_e59f602c-c0a0-484d-bc1e-d38888f14545" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_e59f602c-c0a0-484d-bc1e-d38888f14545" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_9667250a-4918-4f34-aac2-49d70cd04b43" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_9667250a-4918-4f34-aac2-49d70cd04b43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AdjustmentsToAdditionalPaidInCapitalFairValueOfWarrantsIssued_c4138346-b7b9-4048-9f19-db327db0ed82" xlink:href="aqst-20230630.xsd#aqst_AdjustmentsToAdditionalPaidInCapitalFairValueOfWarrantsIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_aqst_AdjustmentsToAdditionalPaidInCapitalFairValueOfWarrantsIssued_c4138346-b7b9-4048-9f19-db327db0ed82" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ClassOfWarrantOrRightWarrantsExercised_f4a8d984-a379-425e-9330-7bbde0479c4f" xlink:href="aqst-20230630.xsd#aqst_ClassOfWarrantOrRightWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_aqst_ClassOfWarrantOrRightWarrantsExercised_f4a8d984-a379-425e-9330-7bbde0479c4f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_1ec6ad3c-e112-462a-a614-eead35a616bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_1ec6ad3c-e112-462a-a614-eead35a616bf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod_258a285f-31c3-42e3-9fd2-624adca5167b" xlink:href="aqst-20230630.xsd#aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_aqst_ClassOfWarrantOrRightWarrantsIssuedDuringPeriod_258a285f-31c3-42e3-9fd2-624adca5167b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_c5a3042b-5a35-4036-8789-48959bece26a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_a5668944-3bc1-4588-a8d3-13fc7deceb84" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_c5a3042b-5a35-4036-8789-48959bece26a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_dc6bbdb2-9385-4749-a7ce-f2c88036d966" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_c5a3042b-5a35-4036-8789-48959bece26a" xlink:to="loc_us-gaap_DebtInstrumentAxis_dc6bbdb2-9385-4749-a7ce-f2c88036d966" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_dc6bbdb2-9385-4749-a7ce-f2c88036d966_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_dc6bbdb2-9385-4749-a7ce-f2c88036d966" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_dc6bbdb2-9385-4749-a7ce-f2c88036d966_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b06fb934-f692-4371-99b6-003e96e2396f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_dc6bbdb2-9385-4749-a7ce-f2c88036d966" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b06fb934-f692-4371-99b6-003e96e2396f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_FirstAdditionalOfferingMember_8465c47f-9b3e-446d-9f3d-71e899ff39a3" xlink:href="aqst-20230630.xsd#aqst_FirstAdditionalOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b06fb934-f692-4371-99b6-003e96e2396f" xlink:to="loc_aqst_FirstAdditionalOfferingMember_8465c47f-9b3e-446d-9f3d-71e899ff39a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_deb9d9e2-f02b-4670-8069-9fb899db61d5" xlink:href="aqst-20230630.xsd#aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b06fb934-f692-4371-99b6-003e96e2396f" xlink:to="loc_aqst_TwelvePointFiveSeniorSecuredNotesDueJune302025Member_deb9d9e2-f02b-4670-8069-9fb899db61d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_6d7dca3e-68f6-4f4d-9f9f-2bb4f3f6c91a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_c5a3042b-5a35-4036-8789-48959bece26a" xlink:to="loc_srt_RangeAxis_6d7dca3e-68f6-4f4d-9f9f-2bb4f3f6c91a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6d7dca3e-68f6-4f4d-9f9f-2bb4f3f6c91a_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_6d7dca3e-68f6-4f4d-9f9f-2bb4f3f6c91a" xlink:to="loc_srt_RangeMember_6d7dca3e-68f6-4f4d-9f9f-2bb4f3f6c91a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5331f4d3-2aeb-4a9b-9c83-c4ffe5a09219" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_6d7dca3e-68f6-4f4d-9f9f-2bb4f3f6c91a" xlink:to="loc_srt_RangeMember_5331f4d3-2aeb-4a9b-9c83-c4ffe5a09219" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c8ecc895-3bce-488d-899f-dc667cf5b299" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_5331f4d3-2aeb-4a9b-9c83-c4ffe5a09219" xlink:to="loc_srt_MinimumMember_c8ecc895-3bce-488d-899f-dc667cf5b299" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_865bf958-929c-40eb-96ab-77161078e88f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_5331f4d3-2aeb-4a9b-9c83-c4ffe5a09219" xlink:to="loc_srt_MaximumMember_865bf958-929c-40eb-96ab-77161078e88f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_4088cff1-6205-4066-9d14-9cf78c9fcc1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_c5a3042b-5a35-4036-8789-48959bece26a" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_4088cff1-6205-4066-9d14-9cf78c9fcc1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_4088cff1-6205-4066-9d14-9cf78c9fcc1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_4088cff1-6205-4066-9d14-9cf78c9fcc1f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_4088cff1-6205-4066-9d14-9cf78c9fcc1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_73f06caa-0d35-40a5-9ee2-d4df67430301" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_4088cff1-6205-4066-9d14-9cf78c9fcc1f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_73f06caa-0d35-40a5-9ee2-d4df67430301" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_PreFundedWarrantsMember_1bee277f-81b7-40d2-ac23-11ae7c008a57" xlink:href="aqst-20230630.xsd#aqst_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_73f06caa-0d35-40a5-9ee2-d4df67430301" xlink:to="loc_aqst_PreFundedWarrantsMember_1bee277f-81b7-40d2-ac23-11ae7c008a57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_CommonStockWarrantsMember_379b0397-8408-49be-a191-bd3684eb342c" xlink:href="aqst-20230630.xsd#aqst_CommonStockWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_73f06caa-0d35-40a5-9ee2-d4df67430301" xlink:to="loc_aqst_CommonStockWarrantsMember_379b0397-8408-49be-a191-bd3684eb342c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_IssuanceAxis_8f18ee44-cda5-4237-ad7f-dc91850fdac9" xlink:href="aqst-20230630.xsd#aqst_IssuanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_c5a3042b-5a35-4036-8789-48959bece26a" xlink:to="loc_aqst_IssuanceAxis_8f18ee44-cda5-4237-ad7f-dc91850fdac9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_IssuanceDomain_8f18ee44-cda5-4237-ad7f-dc91850fdac9_default" xlink:href="aqst-20230630.xsd#aqst_IssuanceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aqst_IssuanceAxis_8f18ee44-cda5-4237-ad7f-dc91850fdac9" xlink:to="loc_aqst_IssuanceDomain_8f18ee44-cda5-4237-ad7f-dc91850fdac9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_IssuanceDomain_ae34134e-e983-4914-b165-e23d8181cbd2" xlink:href="aqst-20230630.xsd#aqst_IssuanceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aqst_IssuanceAxis_8f18ee44-cda5-4237-ad7f-dc91850fdac9" xlink:to="loc_aqst_IssuanceDomain_ae34134e-e983-4914-b165-e23d8181cbd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_PublicEquityMember_7a0d277d-453a-40ad-ac43-49118b1e6f5b" xlink:href="aqst-20230630.xsd#aqst_PublicEquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_IssuanceDomain_ae34134e-e983-4914-b165-e23d8181cbd2" xlink:to="loc_aqst_PublicEquityMember_7a0d277d-453a-40ad-ac43-49118b1e6f5b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/SaleofFutureRevenueNarrativeDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#SaleofFutureRevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/SaleofFutureRevenueNarrativeDetails" xlink:type="extended" id="ifbc5001639854232af8d41b4394d8345_SaleofFutureRevenueNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ProceedsFromSaleOfFutureRevenuesNet_4d8cf428-ee9b-44d8-8399-888597e1db75" xlink:href="aqst-20230630.xsd#aqst_ProceedsFromSaleOfFutureRevenuesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:to="loc_aqst_ProceedsFromSaleOfFutureRevenuesNet_4d8cf428-ee9b-44d8-8399-888597e1db75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ContingentMonetizationAgreementMilestonePayment_e8ff0149-7a04-45b1-8d9c-7ae50c746630" xlink:href="aqst-20230630.xsd#aqst_ContingentMonetizationAgreementMilestonePayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:to="loc_aqst_ContingentMonetizationAgreementMilestonePayment_e8ff0149-7a04-45b1-8d9c-7ae50c746630" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfFinancingCosts_4cf6a2f9-8169-4aba-931b-1293eff5f176" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:to="loc_us-gaap_PaymentsOfFinancingCosts_4cf6a2f9-8169-4aba-931b-1293eff5f176" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_8994e9e8-e93d-4f4d-8bb7-88afd3d7906f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_8994e9e8-e93d-4f4d-8bb7-88afd3d7906f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_MinimumAnnualRoyaltyReceivable_0e95dc88-5611-4761-8c8e-ce1c15f99618" xlink:href="aqst-20230630.xsd#aqst_MinimumAnnualRoyaltyReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:to="loc_aqst_MinimumAnnualRoyaltyReceivable_0e95dc88-5611-4761-8c8e-ce1c15f99618" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_202c7814-1a7c-46a4-956c-41c2f0c793ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_202c7814-1a7c-46a4-956c-41c2f0c793ea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_a372c186-a2a3-4cbd-a13b-7cfb27f6bbe9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fa0a37f3-0366-4a3a-9384-44d970d2f7e8" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_a372c186-a2a3-4cbd-a13b-7cfb27f6bbe9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_b2bb83c8-26ee-4d8e-b793-a3e932e05449" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a372c186-a2a3-4cbd-a13b-7cfb27f6bbe9" xlink:to="loc_us-gaap_CreditFacilityAxis_b2bb83c8-26ee-4d8e-b793-a3e932e05449" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_b2bb83c8-26ee-4d8e-b793-a3e932e05449_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_b2bb83c8-26ee-4d8e-b793-a3e932e05449" xlink:to="loc_us-gaap_CreditFacilityDomain_b2bb83c8-26ee-4d8e-b793-a3e932e05449_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_0f02bb27-174c-41f1-b924-0db560ed5320" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_b2bb83c8-26ee-4d8e-b793-a3e932e05449" xlink:to="loc_us-gaap_CreditFacilityDomain_0f02bb27-174c-41f1-b924-0db560ed5320" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_MonetizationAgreementMember_fe70547e-1fbd-4c6c-8eeb-2b48531d659e" xlink:href="aqst-20230630.xsd#aqst_MonetizationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_0f02bb27-174c-41f1-b924-0db560ed5320" xlink:to="loc_aqst_MonetizationAgreementMember_fe70547e-1fbd-4c6c-8eeb-2b48531d659e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_aadb3a99-455f-45dc-aed1-bc85f0d8f1b2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a372c186-a2a3-4cbd-a13b-7cfb27f6bbe9" xlink:to="loc_us-gaap_TypeOfArrangementAxis_aadb3a99-455f-45dc-aed1-bc85f0d8f1b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_aadb3a99-455f-45dc-aed1-bc85f0d8f1b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_aadb3a99-455f-45dc-aed1-bc85f0d8f1b2" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_aadb3a99-455f-45dc-aed1-bc85f0d8f1b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_5670a5b8-b318-4a4c-a1c8-90ccad5bb5d6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_aadb3a99-455f-45dc-aed1-bc85f0d8f1b2" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_5670a5b8-b318-4a4c-a1c8-90ccad5bb5d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_MarathonPangolinRoyaltyLLCMember_a687d315-3037-49ad-b8f5-4a4c63670d1d" xlink:href="aqst-20230630.xsd#aqst_MarathonPangolinRoyaltyLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_5670a5b8-b318-4a4c-a1c8-90ccad5bb5d6" xlink:to="loc_aqst_MarathonPangolinRoyaltyLLCMember_a687d315-3037-49ad-b8f5-4a4c63670d1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_f4d3e4e5-6161-4572-9794-dd1dc27c0bbc" xlink:href="aqst-20230630.xsd#aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_5670a5b8-b318-4a4c-a1c8-90ccad5bb5d6" xlink:to="loc_aqst_LicenseAgreementWithSunovionPharmaceuticalsIncMember_f4d3e4e5-6161-4572-9794-dd1dc27c0bbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b145ea9f-d8a5-41f0-b599-58c0740af7f0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a372c186-a2a3-4cbd-a13b-7cfb27f6bbe9" xlink:to="loc_srt_RangeAxis_b145ea9f-d8a5-41f0-b599-58c0740af7f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b145ea9f-d8a5-41f0-b599-58c0740af7f0_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b145ea9f-d8a5-41f0-b599-58c0740af7f0" xlink:to="loc_srt_RangeMember_b145ea9f-d8a5-41f0-b599-58c0740af7f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8208930c-1fd6-4016-8e51-af782b5e938f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b145ea9f-d8a5-41f0-b599-58c0740af7f0" xlink:to="loc_srt_RangeMember_8208930c-1fd6-4016-8e51-af782b5e938f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_602feed5-f27c-4595-a958-7a6f20a995b9" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8208930c-1fd6-4016-8e51-af782b5e938f" xlink:to="loc_srt_MaximumMember_602feed5-f27c-4595-a958-7a6f20a995b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_cf337f01-341a-4758-a39b-11023472407a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a372c186-a2a3-4cbd-a13b-7cfb27f6bbe9" xlink:to="loc_srt_ProductOrServiceAxis_cf337f01-341a-4758-a39b-11023472407a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_cf337f01-341a-4758-a39b-11023472407a_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_cf337f01-341a-4758-a39b-11023472407a" xlink:to="loc_srt_ProductsAndServicesDomain_cf337f01-341a-4758-a39b-11023472407a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_00e1e249-c511-4bef-a49a-bfd5e1b55875" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_cf337f01-341a-4758-a39b-11023472407a" xlink:to="loc_srt_ProductsAndServicesDomain_00e1e249-c511-4bef-a49a-bfd5e1b55875" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_9474d2ce-606c-4a87-9885-a1f347489faf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_00e1e249-c511-4bef-a49a-bfd5e1b55875" xlink:to="loc_us-gaap_RoyaltyMember_9474d2ce-606c-4a87-9885-a1f347489faf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/SaleofFutureRevenueRoyaltyObligationDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#SaleofFutureRevenueRoyaltyObligationDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/SaleofFutureRevenueRoyaltyObligationDetails" xlink:type="extended" id="i5c1e16618ad04a108c6b36c98896b239_SaleofFutureRevenueRoyaltyObligationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_579f6b0e-3424-43ac-a9bc-2f7e9130d27c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SaleOfFutureRevenueRollForward_1978e18c-fe44-4382-8d22-2707d375b7bf" xlink:href="aqst-20230630.xsd#aqst_SaleOfFutureRevenueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_579f6b0e-3424-43ac-a9bc-2f7e9130d27c" xlink:to="loc_aqst_SaleOfFutureRevenueRollForward_1978e18c-fe44-4382-8d22-2707d375b7bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LiabilitiesSaleOfFutureRoyalties_9268b886-5cfc-469e-bacb-8dee2f69ab6d" xlink:href="aqst-20230630.xsd#aqst_LiabilitiesSaleOfFutureRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SaleOfFutureRevenueRollForward_1978e18c-fe44-4382-8d22-2707d375b7bf" xlink:to="loc_aqst_LiabilitiesSaleOfFutureRoyalties_9268b886-5cfc-469e-bacb-8dee2f69ab6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_19094e68-4b44-43f0-bb3d-00299395fa1a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SaleOfFutureRevenueRollForward_1978e18c-fe44-4382-8d22-2707d375b7bf" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_19094e68-4b44-43f0-bb3d-00299395fa1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_549e021f-ec30-44c0-b7a7-60dcb87b08e0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SaleOfFutureRevenueRollForward_1978e18c-fe44-4382-8d22-2707d375b7bf" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_549e021f-ec30-44c0-b7a7-60dcb87b08e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_InterestExpenseSaleOfFutureRevenuesExcludingAmortization_56713a3d-9dab-4ae8-a44d-1cb94644e9ee" xlink:href="aqst-20230630.xsd#aqst_InterestExpenseSaleOfFutureRevenuesExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aqst_SaleOfFutureRevenueRollForward_1978e18c-fe44-4382-8d22-2707d375b7bf" xlink:to="loc_aqst_InterestExpenseSaleOfFutureRevenuesExcludingAmortization_56713a3d-9dab-4ae8-a44d-1cb94644e9ee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LiabilitiesSaleOfFutureRoyalties_a6d705d1-0a29-490c-9dbc-01b93522c32a" xlink:href="aqst-20230630.xsd#aqst_LiabilitiesSaleOfFutureRoyalties"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_LiabilitiesSaleOfFutureRoyaltiesCurrent_3a4fc57c-41ea-4fb2-b84a-c27fa59c3b31" xlink:href="aqst-20230630.xsd#aqst_LiabilitiesSaleOfFutureRoyaltiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_579f6b0e-3424-43ac-a9bc-2f7e9130d27c" xlink:to="loc_aqst_LiabilitiesSaleOfFutureRoyaltiesCurrent_3a4fc57c-41ea-4fb2-b84a-c27fa59c3b31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_2903bfde-66fc-419c-a87d-936d384e05eb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_579f6b0e-3424-43ac-a9bc-2f7e9130d27c" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_2903bfde-66fc-419c-a87d-936d384e05eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_2a531e13-d22a-4c1d-8039-34f41f911a18" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2903bfde-66fc-419c-a87d-936d384e05eb" xlink:to="loc_srt_ProductOrServiceAxis_2a531e13-d22a-4c1d-8039-34f41f911a18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_2a531e13-d22a-4c1d-8039-34f41f911a18_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_2a531e13-d22a-4c1d-8039-34f41f911a18" xlink:to="loc_srt_ProductsAndServicesDomain_2a531e13-d22a-4c1d-8039-34f41f911a18_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_0477fbda-83c0-41da-887d-7739e8a7d384" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_2a531e13-d22a-4c1d-8039-34f41f911a18" xlink:to="loc_srt_ProductsAndServicesDomain_0477fbda-83c0-41da-887d-7739e8a7d384" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_5b91eaca-ae8d-4527-adb8-0d5c1dcb510a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_0477fbda-83c0-41da-887d-7739e8a7d384" xlink:to="loc_us-gaap_RoyaltyMember_5b91eaca-ae8d-4527-adb8-0d5c1dcb510a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/NetEarningsLossPerShareBasicandDilutedNetLossPerShareDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#NetEarningsLossPerShareBasicandDilutedNetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/NetEarningsLossPerShareBasicandDilutedNetLossPerShareDetails" xlink:type="extended" id="i81296c74025d40d584a9bf71c26cda8f_NetEarningsLossPerShareBasicandDilutedNetLossPerShareDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_0b8fb9f7-5e0d-43cf-8d55-e0081d488d72" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_NetIncomeLoss_0b8fb9f7-5e0d-43cf-8d55-e0081d488d72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_f0bf2649-ce18-47b2-a178-9b8d17e56783" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_f0bf2649-ce18-47b2-a178-9b8d17e56783" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_6a16e3f1-9acc-480f-bdc5-e189b6c47776" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_6a16e3f1-9acc-480f-bdc5-e189b6c47776" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_48e34786-18b6-4c89-862e-31b492c8c923" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_48e34786-18b6-4c89-862e-31b492c8c923" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_0a60d3eb-1eea-40df-b90a-f00862f775d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_EarningsPerShareBasic_0a60d3eb-1eea-40df-b90a-f00862f775d3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_18737d65-6287-43b5-824a-bab509f8b11a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_EarningsPerShareDiluted_18737d65-6287-43b5-824a-bab509f8b11a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_17c31bf4-24c3-4b98-abc4-b5f066cb5aa9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_17c31bf4-24c3-4b98-abc4-b5f066cb5aa9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_6e062e13-a07f-4d40-9965-ca8a68a24f53" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_78a3c045-65da-4d9d-a814-3244e75cd6c9" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_6e062e13-a07f-4d40-9965-ca8a68a24f53" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_bdb3613c-bd86-4d46-a519-9e50a813945e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_6e062e13-a07f-4d40-9965-ca8a68a24f53" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_bdb3613c-bd86-4d46-a519-9e50a813945e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_bdb3613c-bd86-4d46-a519-9e50a813945e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_bdb3613c-bd86-4d46-a519-9e50a813945e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_bdb3613c-bd86-4d46-a519-9e50a813945e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_203b80fb-a8a8-485b-a557-785b0ace47a7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_bdb3613c-bd86-4d46-a519-9e50a813945e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_203b80fb-a8a8-485b-a557-785b0ace47a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_4d614b3c-1f90-4b0f-a0c9-cd07949a0024" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_203b80fb-a8a8-485b-a557-785b0ace47a7" xlink:to="loc_us-gaap_EmployeeStockOptionMember_4d614b3c-1f90-4b0f-a0c9-cd07949a0024" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_c4752e15-e874-4de6-af7d-cb127eadd3e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_203b80fb-a8a8-485b-a557-785b0ace47a7" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_c4752e15-e874-4de6-af7d-cb127eadd3e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_0f2c58a5-8100-4c38-9dc6-cc03daf95e1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_203b80fb-a8a8-485b-a557-785b0ace47a7" xlink:to="loc_us-gaap_WarrantMember_0f2c58a5-8100-4c38-9dc6-cc03daf95e1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityUnitPurchaseAgreementsMember_16999340-a198-48ed-b229-428517beb825" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityUnitPurchaseAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_203b80fb-a8a8-485b-a557-785b0ace47a7" xlink:to="loc_us-gaap_EquityUnitPurchaseAgreementsMember_16999340-a198-48ed-b229-428517beb825" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/ShareBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#ShareBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/ShareBasedCompensationExpenseDetails" xlink:type="extended" id="ie366f915d1c8470a877f41da2d9bfdfe_ShareBasedCompensationExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e1d6fd61-1377-4774-aad1-d040351697c5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAbstract_1025785e-172f-49f2-be21-26690b4af1f7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e1d6fd61-1377-4774-aad1-d040351697c5" xlink:to="loc_us-gaap_ShareBasedCompensationAbstract_1025785e-172f-49f2-be21-26690b4af1f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_f09465db-e725-4d25-9ab8-9268da050d12" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAbstract_1025785e-172f-49f2-be21-26690b4af1f7" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_f09465db-e725-4d25-9ab8-9268da050d12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a07cb3d9-ee74-4277-92bd-16432fb33b8c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e1d6fd61-1377-4774-aad1-d040351697c5" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a07cb3d9-ee74-4277-92bd-16432fb33b8c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_517abbcd-9065-43c2-ac63-3424532fc63f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a07cb3d9-ee74-4277-92bd-16432fb33b8c" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_517abbcd-9065-43c2-ac63-3424532fc63f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_517abbcd-9065-43c2-ac63-3424532fc63f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_517abbcd-9065-43c2-ac63-3424532fc63f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_517abbcd-9065-43c2-ac63-3424532fc63f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_968ddcbe-0a31-4df1-a515-59fef7fe842c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_517abbcd-9065-43c2-ac63-3424532fc63f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_968ddcbe-0a31-4df1-a515-59fef7fe842c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ManufacturingAndSupplyMember_c708b901-65c5-4ba5-be2d-a3209d15e82d" xlink:href="aqst-20230630.xsd#aqst_ManufacturingAndSupplyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_968ddcbe-0a31-4df1-a515-59fef7fe842c" xlink:to="loc_aqst_ManufacturingAndSupplyMember_c708b901-65c5-4ba5-be2d-a3209d15e82d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_72d1c45e-0ee7-4516-bc0f-fd2d9ff14b01" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_968ddcbe-0a31-4df1-a515-59fef7fe842c" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_72d1c45e-0ee7-4516-bc0f-fd2d9ff14b01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_d0d4223b-1dae-4c63-904a-075f9d8b0708" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_968ddcbe-0a31-4df1-a515-59fef7fe842c" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_d0d4223b-1dae-4c63-904a-075f9d8b0708" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_238381df-0728-4581-a66c-b887a8625af4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a07cb3d9-ee74-4277-92bd-16432fb33b8c" xlink:to="loc_us-gaap_AwardTypeAxis_238381df-0728-4581-a66c-b887a8625af4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_238381df-0728-4581-a66c-b887a8625af4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_238381df-0728-4581-a66c-b887a8625af4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_238381df-0728-4581-a66c-b887a8625af4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d4d07a65-d18b-4970-8804-17d32c382c41" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_238381df-0728-4581-a66c-b887a8625af4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d4d07a65-d18b-4970-8804-17d32c382c41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_6a954080-3790-419e-92c0-fcc78efbcb1c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d4d07a65-d18b-4970-8804-17d32c382c41" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_6a954080-3790-419e-92c0-fcc78efbcb1c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_c9af08f8-4c33-4216-ba0a-cea6265839e6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d4d07a65-d18b-4970-8804-17d32c382c41" xlink:to="loc_us-gaap_EmployeeStockOptionMember_c9af08f8-4c33-4216-ba0a-cea6265839e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_23a51a17-9bcc-46a5-9b53-61d14c6f280c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d4d07a65-d18b-4970-8804-17d32c382c41" xlink:to="loc_us-gaap_EmployeeStockMember_23a51a17-9bcc-46a5-9b53-61d14c6f280c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/ShareBasedCompensationRestrictedStockUnitAwardsDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#ShareBasedCompensationRestrictedStockUnitAwardsDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/ShareBasedCompensationRestrictedStockUnitAwardsDetails" xlink:type="extended" id="ic78b748e146047fdae7bf4b90ae02414_ShareBasedCompensationRestrictedStockUnitAwardsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_fca67cc8-41e1-45f8-bdd4-032d153129bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_dc6c870a-a963-4a96-b1a6-0b57c425d195" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_fca67cc8-41e1-45f8-bdd4-032d153129bf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_dc6c870a-a963-4a96-b1a6-0b57c425d195" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_7cace516-4163-489b-b30a-6a1485139988" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_dc6c870a-a963-4a96-b1a6-0b57c425d195" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_7cace516-4163-489b-b30a-6a1485139988" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b09ef869-ccc3-4e07-b232-f6bf5ab790da" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_dc6c870a-a963-4a96-b1a6-0b57c425d195" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b09ef869-ccc3-4e07-b232-f6bf5ab790da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_b655a4e9-63e4-48c0-8132-41338a20eada" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_dc6c870a-a963-4a96-b1a6-0b57c425d195" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_b655a4e9-63e4-48c0-8132-41338a20eada" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_854d65e0-ed03-4dc4-9fa7-65a0f53d9f52" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_dc6c870a-a963-4a96-b1a6-0b57c425d195" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_854d65e0-ed03-4dc4-9fa7-65a0f53d9f52" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_a52417f4-7ced-4856-ae67-a749a74e9460" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInShares_1f27b4e0-0e4e-4d3a-8b44-5e15f4d6b7a8" xlink:href="aqst-20230630.xsd#aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_fca67cc8-41e1-45f8-bdd4-032d153129bf" xlink:to="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInShares_1f27b4e0-0e4e-4d3a-8b44-5e15f4d6b7a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0817ac6b-a209-415b-b984-0f0894929c91" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_fca67cc8-41e1-45f8-bdd4-032d153129bf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0817ac6b-a209-415b-b984-0f0894929c91" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_228746ed-fd0d-4d04-91e8-d6c0f846dc9b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0817ac6b-a209-415b-b984-0f0894929c91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_228746ed-fd0d-4d04-91e8-d6c0f846dc9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_37b55c65-0830-4985-8f22-dcf5d54a515d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0817ac6b-a209-415b-b984-0f0894929c91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_37b55c65-0830-4985-8f22-dcf5d54a515d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_11db246c-0d95-4269-a5d1-b0ead24321b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0817ac6b-a209-415b-b984-0f0894929c91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_11db246c-0d95-4269-a5d1-b0ead24321b3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_c2574569-e9ca-400b-baa1-cc449133510e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0817ac6b-a209-415b-b984-0f0894929c91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_c2574569-e9ca-400b-baa1-cc449133510e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_00d714d5-de8d-46ab-9d3b-d09a5a449465" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsEstimatedGrantDateFairValue_047e4940-4bea-425a-9f1b-f89d40023c0a" xlink:href="aqst-20230630.xsd#aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsEstimatedGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_fca67cc8-41e1-45f8-bdd4-032d153129bf" xlink:to="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsEstimatedGrantDateFairValue_047e4940-4bea-425a-9f1b-f89d40023c0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2e2497a3-ccd9-42b2-aa26-4998577e72bd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_fca67cc8-41e1-45f8-bdd4-032d153129bf" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2e2497a3-ccd9-42b2-aa26-4998577e72bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_66441f0f-8bf4-41fb-8c23-21e05d339224" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2e2497a3-ccd9-42b2-aa26-4998577e72bd" xlink:to="loc_us-gaap_AwardTypeAxis_66441f0f-8bf4-41fb-8c23-21e05d339224" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_66441f0f-8bf4-41fb-8c23-21e05d339224_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_66441f0f-8bf4-41fb-8c23-21e05d339224" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_66441f0f-8bf4-41fb-8c23-21e05d339224_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_195d1fc6-7b79-4717-a926-83888cac031e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_66441f0f-8bf4-41fb-8c23-21e05d339224" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_195d1fc6-7b79-4717-a926-83888cac031e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_9358698c-c55a-4369-b538-c6c4466628dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_195d1fc6-7b79-4717-a926-83888cac031e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_9358698c-c55a-4369-b538-c6c4466628dd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/ShareBasedCompensationPerformanceBasedDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#ShareBasedCompensationPerformanceBasedDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/ShareBasedCompensationPerformanceBasedDetails" xlink:type="extended" id="i58b19f9c0c0e490db56cb4b390363982_ShareBasedCompensationPerformanceBasedDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_633dd07a-697e-4209-92dc-36dc3b4a7ae5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_97aa86b4-ce81-4404-975a-24438956d582" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_633dd07a-697e-4209-92dc-36dc3b4a7ae5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_97aa86b4-ce81-4404-975a-24438956d582" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_7f27de66-f017-4081-91ea-8d68c715ce3f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_97aa86b4-ce81-4404-975a-24438956d582" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_7f27de66-f017-4081-91ea-8d68c715ce3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3bf03f74-7ca0-4b9e-86c8-89ba137bf676" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_97aa86b4-ce81-4404-975a-24438956d582" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3bf03f74-7ca0-4b9e-86c8-89ba137bf676" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_3a95067b-31e0-4165-8694-dc695002eb52" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_97aa86b4-ce81-4404-975a-24438956d582" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_3a95067b-31e0-4165-8694-dc695002eb52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_2b1ff8c3-a7ab-4380-9160-12dd2d835566" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_97aa86b4-ce81-4404-975a-24438956d582" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_2b1ff8c3-a7ab-4380-9160-12dd2d835566" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInShares_4d76335c-0246-4e11-9715-f5e585ba4124" xlink:href="aqst-20230630.xsd#aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_633dd07a-697e-4209-92dc-36dc3b4a7ae5" xlink:to="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInShares_4d76335c-0246-4e11-9715-f5e585ba4124" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_8d478249-53be-41bc-b34e-e8a88fcb5e33" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_633dd07a-697e-4209-92dc-36dc3b4a7ae5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_8d478249-53be-41bc-b34e-e8a88fcb5e33" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_28f21eef-3b75-457d-8225-0c3603efd3e7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_8d478249-53be-41bc-b34e-e8a88fcb5e33" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_28f21eef-3b75-457d-8225-0c3603efd3e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_225fbb38-fe6f-40bc-820f-da0f54464a19" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_8d478249-53be-41bc-b34e-e8a88fcb5e33" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_225fbb38-fe6f-40bc-820f-da0f54464a19" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_80c7186b-016f-429c-84c5-38af603f97d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_8d478249-53be-41bc-b34e-e8a88fcb5e33" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_80c7186b-016f-429c-84c5-38af603f97d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_25195db8-d0c3-411d-99a0-d9ada816e72a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_8d478249-53be-41bc-b34e-e8a88fcb5e33" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_25195db8-d0c3-411d-99a0-d9ada816e72a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsEstimatedGrantDateFairValue_01638e17-3a71-4587-a2a4-eb0084dd7ac4" xlink:href="aqst-20230630.xsd#aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsEstimatedGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_633dd07a-697e-4209-92dc-36dc3b4a7ae5" xlink:to="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsEstimatedGrantDateFairValue_01638e17-3a71-4587-a2a4-eb0084dd7ac4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ce8f3326-450f-4373-86f0-6f0268a346d1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_633dd07a-697e-4209-92dc-36dc3b4a7ae5" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ce8f3326-450f-4373-86f0-6f0268a346d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f96ce44f-432a-45bc-8a0d-9a06241b1d0d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ce8f3326-450f-4373-86f0-6f0268a346d1" xlink:to="loc_us-gaap_AwardTypeAxis_f96ce44f-432a-45bc-8a0d-9a06241b1d0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f96ce44f-432a-45bc-8a0d-9a06241b1d0d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f96ce44f-432a-45bc-8a0d-9a06241b1d0d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f96ce44f-432a-45bc-8a0d-9a06241b1d0d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f2dab5fc-cff8-401e-9441-3a8b83f88557" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f96ce44f-432a-45bc-8a0d-9a06241b1d0d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f2dab5fc-cff8-401e-9441-3a8b83f88557" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_2654e07b-35a6-490a-82c9-795b70be4246" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f2dab5fc-cff8-401e-9441-3a8b83f88557" xlink:to="loc_us-gaap_PerformanceSharesMember_2654e07b-35a6-490a-82c9-795b70be4246" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/ShareBasedCompensationStockOptionActivityDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#ShareBasedCompensationStockOptionActivityDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/ShareBasedCompensationStockOptionActivityDetails" xlink:type="extended" id="iae8396a4ec174d5a95539a12dea7b25c_ShareBasedCompensationStockOptionActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4a4ea7c8-ef99-42c4-b7a4-9e2a08d53e13" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_310aa4d0-bd6f-4a81-8fa7-1e7f7cdeaaa6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4a4ea7c8-ef99-42c4-b7a4-9e2a08d53e13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_310aa4d0-bd6f-4a81-8fa7-1e7f7cdeaaa6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_27b8d876-30bf-4098-a46a-2b2e22718a38" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_310aa4d0-bd6f-4a81-8fa7-1e7f7cdeaaa6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_27b8d876-30bf-4098-a46a-2b2e22718a38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_92919683-d6d1-4660-9234-fffac1416472" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_310aa4d0-bd6f-4a81-8fa7-1e7f7cdeaaa6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_92919683-d6d1-4660-9234-fffac1416472" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedForfeituresAndExpirationsInPeriod_72190b41-8c18-404a-9b09-0129f3f589bd" xlink:href="aqst-20230630.xsd#aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedForfeituresAndExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_310aa4d0-bd6f-4a81-8fa7-1e7f7cdeaaa6" xlink:to="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedForfeituresAndExpirationsInPeriod_72190b41-8c18-404a-9b09-0129f3f589bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_8855edf5-efa2-4ffa-96ad-3feb3a00fad4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_310aa4d0-bd6f-4a81-8fa7-1e7f7cdeaaa6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_8855edf5-efa2-4ffa-96ad-3feb3a00fad4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_16222a9b-9b89-4952-952d-ae51d000d45f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4a4ea7c8-ef99-42c4-b7a4-9e2a08d53e13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_16222a9b-9b89-4952-952d-ae51d000d45f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_a1e683dd-ed68-499e-9d00-8448fb106da0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4a4ea7c8-ef99-42c4-b7a4-9e2a08d53e13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_a1e683dd-ed68-499e-9d00-8448fb106da0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_705df4cd-abe2-44f8-bd1d-89d24b8b26a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_a1e683dd-ed68-499e-9d00-8448fb106da0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_705df4cd-abe2-44f8-bd1d-89d24b8b26a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_4a19f9c8-4f4d-45a4-8918-c4909ab3a36b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_a1e683dd-ed68-499e-9d00-8448fb106da0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_4a19f9c8-4f4d-45a4-8918-c4909ab3a36b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice_2fa19da1-9641-42fb-9d54-86f4da99fe7b" xlink:href="aqst-20230630.xsd#aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_a1e683dd-ed68-499e-9d00-8448fb106da0" xlink:to="loc_aqst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice_2fa19da1-9641-42fb-9d54-86f4da99fe7b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_7c3f5c25-2157-40a0-900e-eb86b6d48944" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_a1e683dd-ed68-499e-9d00-8448fb106da0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_7c3f5c25-2157-40a0-900e-eb86b6d48944" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_1ce1822f-7fef-4b5e-8d05-6af212b588ee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4a4ea7c8-ef99-42c4-b7a4-9e2a08d53e13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_1ce1822f-7fef-4b5e-8d05-6af212b588ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_67c42317-74f9-4fd4-b57a-ecf35bfe2f44" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4a4ea7c8-ef99-42c4-b7a4-9e2a08d53e13" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_67c42317-74f9-4fd4-b57a-ecf35bfe2f44" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e0226c91-ccdd-4cf8-a147-eefd066d93b8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_67c42317-74f9-4fd4-b57a-ecf35bfe2f44" xlink:to="loc_us-gaap_AwardTypeAxis_e0226c91-ccdd-4cf8-a147-eefd066d93b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e0226c91-ccdd-4cf8-a147-eefd066d93b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e0226c91-ccdd-4cf8-a147-eefd066d93b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e0226c91-ccdd-4cf8-a147-eefd066d93b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8217d2e-bd18-49ca-8b30-8956e546bf0d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e0226c91-ccdd-4cf8-a147-eefd066d93b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8217d2e-bd18-49ca-8b30-8956e546bf0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_b8abed3d-b19c-4e00-ba0a-88f81fb30d9b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8217d2e-bd18-49ca-8b30-8956e546bf0d" xlink:to="loc_us-gaap_EmployeeStockOptionMember_b8abed3d-b19c-4e00-ba0a-88f81fb30d9b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/ShareBasedCompensationValuationAssumptionsforDeterminationofFairValueofOptionsDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#ShareBasedCompensationValuationAssumptionsforDeterminationofFairValueofOptionsDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/ShareBasedCompensationValuationAssumptionsforDeterminationofFairValueofOptionsDetails" xlink:type="extended" id="i9671b4eef9144f47983369ad3727fc7f_ShareBasedCompensationValuationAssumptionsforDeterminationofFairValueofOptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aefdf087-7f7d-4502-8a6e-e6f593dcc5df" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_a7db09bc-49b4-4e44-a21c-3f0c6fe030fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aefdf087-7f7d-4502-8a6e-e6f593dcc5df" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_a7db09bc-49b4-4e44-a21c-3f0c6fe030fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_e0f2b3b9-0e4a-4676-9ced-fa12b9a1cc72" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aefdf087-7f7d-4502-8a6e-e6f593dcc5df" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_e0f2b3b9-0e4a-4676-9ced-fa12b9a1cc72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_50ab86f9-2e7c-44e3-addd-84450223d90a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aefdf087-7f7d-4502-8a6e-e6f593dcc5df" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_50ab86f9-2e7c-44e3-addd-84450223d90a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_d81b66ae-4c86-4a93-8b18-9e2a9108102a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aefdf087-7f7d-4502-8a6e-e6f593dcc5df" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_d81b66ae-4c86-4a93-8b18-9e2a9108102a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_eb5f0981-f10a-4494-9dc6-a4485da29557" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aefdf087-7f7d-4502-8a6e-e6f593dcc5df" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_eb5f0981-f10a-4494-9dc6-a4485da29557" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_cb90a3b7-13f2-4330-bdc5-c817fe15f261" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_eb5f0981-f10a-4494-9dc6-a4485da29557" xlink:to="loc_us-gaap_AwardTypeAxis_cb90a3b7-13f2-4330-bdc5-c817fe15f261" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cb90a3b7-13f2-4330-bdc5-c817fe15f261_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_cb90a3b7-13f2-4330-bdc5-c817fe15f261" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cb90a3b7-13f2-4330-bdc5-c817fe15f261_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_20c3a0cc-81a5-4dbc-bdc8-b5caa486ed79" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_cb90a3b7-13f2-4330-bdc5-c817fe15f261" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_20c3a0cc-81a5-4dbc-bdc8-b5caa486ed79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_82d8f4c4-321f-4d5d-9d93-3ef595d72ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_20c3a0cc-81a5-4dbc-bdc8-b5caa486ed79" xlink:to="loc_us-gaap_EmployeeStockOptionMember_82d8f4c4-321f-4d5d-9d93-3ef595d72ce6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_7fe88a87-6d49-44e2-9440-f2395cda41f9" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_eb5f0981-f10a-4494-9dc6-a4485da29557" xlink:to="loc_srt_RangeAxis_7fe88a87-6d49-44e2-9440-f2395cda41f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_7fe88a87-6d49-44e2-9440-f2395cda41f9_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_7fe88a87-6d49-44e2-9440-f2395cda41f9" xlink:to="loc_srt_RangeMember_7fe88a87-6d49-44e2-9440-f2395cda41f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0624d355-c85e-4738-87e0-7d4def309d8e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_7fe88a87-6d49-44e2-9440-f2395cda41f9" xlink:to="loc_srt_RangeMember_0624d355-c85e-4738-87e0-7d4def309d8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3ab0b76d-57f5-45d0-bb96-82ae8b076643" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_0624d355-c85e-4738-87e0-7d4def309d8e" xlink:to="loc_srt_MinimumMember_3ab0b76d-57f5-45d0-bb96-82ae8b076643" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#ShareBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="extended" id="i632f76ec5674481f8ffc84182207ca44_ShareBasedCompensationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_5e9fa776-50d5-4815-a19d-18702835a69d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_5e9fa776-50d5-4815-a19d-18702835a69d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_69a03b54-68b6-4a73-a3bf-39589828d66a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_69a03b54-68b6-4a73-a3bf-39589828d66a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_3d2776f5-4ae9-40b2-9728-7bdf57be3468" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_3d2776f5-4ae9-40b2-9728-7bdf57be3468" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_33f1a57f-726c-496d-a14f-7584b0c35922" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_33f1a57f-726c-496d-a14f-7584b0c35922" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_873f23d7-d1c4-41a9-b991-83f1d4969349" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_us-gaap_SharePrice_873f23d7-d1c4-41a9-b991-83f1d4969349" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_e46f0b35-a6f0-4983-810e-7d64848a4a55" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_e46f0b35-a6f0-4983-810e-7d64848a4a55" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_InducementEquityCommonStockOptionsOutstandingShares_c6bd58e3-e54e-4015-8cde-7ced3e8e3856" xlink:href="aqst-20230630.xsd#aqst_InducementEquityCommonStockOptionsOutstandingShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_aqst_InducementEquityCommonStockOptionsOutstandingShares_c6bd58e3-e54e-4015-8cde-7ced3e8e3856" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f64c3924-fe03-4a1c-ac09-dd2fc1c3f1d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cd2fa424-1127-42fc-94b4-5fd67ae934fb" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f64c3924-fe03-4a1c-ac09-dd2fc1c3f1d3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b7151a70-afea-4c9f-b2bb-bd2d4c86db1c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f64c3924-fe03-4a1c-ac09-dd2fc1c3f1d3" xlink:to="loc_us-gaap_AwardTypeAxis_b7151a70-afea-4c9f-b2bb-bd2d4c86db1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b7151a70-afea-4c9f-b2bb-bd2d4c86db1c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b7151a70-afea-4c9f-b2bb-bd2d4c86db1c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b7151a70-afea-4c9f-b2bb-bd2d4c86db1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_225fd69f-9f14-4c48-a2d4-878886410989" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b7151a70-afea-4c9f-b2bb-bd2d4c86db1c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_225fd69f-9f14-4c48-a2d4-878886410989" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_76178690-e5f5-43c7-b018-4d9b10ef61c7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_225fd69f-9f14-4c48-a2d4-878886410989" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_76178690-e5f5-43c7-b018-4d9b10ef61c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_5fc67db4-fca2-47fa-a02b-51c0432aad1d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_225fd69f-9f14-4c48-a2d4-878886410989" xlink:to="loc_us-gaap_PerformanceSharesMember_5fc67db4-fca2-47fa-a02b-51c0432aad1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_e2b19cbf-07cf-4e1d-952a-73973562b872" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_225fd69f-9f14-4c48-a2d4-878886410989" xlink:to="loc_us-gaap_EmployeeStockOptionMember_e2b19cbf-07cf-4e1d-952a-73973562b872" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/ContingenciesDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#ContingenciesDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/ContingenciesDetails" xlink:type="extended" id="ia93addb86c5e40d481784e3e0f98aa46_ContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_0e9ad562-0efe-4cf9-ba31-97740293aea3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyPendingClaimsNumber_a7cdceae-f3f5-4be6-9145-ee22dcdf9c4f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyPendingClaimsNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_0e9ad562-0efe-4cf9-ba31-97740293aea3" xlink:to="loc_us-gaap_LossContingencyPendingClaimsNumber_a7cdceae-f3f5-4be6-9145-ee22dcdf9c4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_6b10f29b-9d6d-4432-a617-7ee7f7c72501" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LitigationSettlementAmountAwardedFromOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_0e9ad562-0efe-4cf9-ba31-97740293aea3" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_6b10f29b-9d6d-4432-a617-7ee7f7c72501" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_e01356e8-9e8b-46f8-ab61-078afc86b0b0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_0e9ad562-0efe-4cf9-ba31-97740293aea3" xlink:to="loc_us-gaap_LossContingenciesTable_e01356e8-9e8b-46f8-ab61-078afc86b0b0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_87613355-2ec8-4669-9908-0fd6c95eeab2" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_e01356e8-9e8b-46f8-ab61-078afc86b0b0" xlink:to="loc_srt_LitigationCaseAxis_87613355-2ec8-4669-9908-0fd6c95eeab2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_87613355-2ec8-4669-9908-0fd6c95eeab2_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_87613355-2ec8-4669-9908-0fd6c95eeab2" xlink:to="loc_srt_LitigationCaseTypeDomain_87613355-2ec8-4669-9908-0fd6c95eeab2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_57b61e2c-bc0b-4d07-8cab-e33ef8341a72" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_87613355-2ec8-4669-9908-0fd6c95eeab2" xlink:to="loc_srt_LitigationCaseTypeDomain_57b61e2c-bc0b-4d07-8cab-e33ef8341a72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NeurelisIncVAquestiveTherapeuticsIncMember_cabd7fdf-8998-489d-a8dd-be82d9d5ce18" xlink:href="aqst-20230630.xsd#aqst_NeurelisIncVAquestiveTherapeuticsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_57b61e2c-bc0b-4d07-8cab-e33ef8341a72" xlink:to="loc_aqst_NeurelisIncVAquestiveTherapeuticsIncMember_cabd7fdf-8998-489d-a8dd-be82d9d5ce18" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://aquestive.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="aqst-20230630.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://aquestive.com/role/SubsequentEventsDetails" xlink:type="extended" id="i362792c266ca4c8f9d6245c36b6bc591_SubsequentEventsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_d879ee8f-137a-44e0-9318-0674d211f899" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_d879ee8f-137a-44e0-9318-0674d211f899" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_cb56135f-09dc-47c7-aaca-74f1fc0791c9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_cb56135f-09dc-47c7-aaca-74f1fc0791c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_0d1f60f5-44e2-4804-b319-61b56efd117b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_0d1f60f5-44e2-4804-b319-61b56efd117b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromWarrantExercises_3465bfcb-3684-4747-8d33-fd35c1a0a521" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromWarrantExercises"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_ProceedsFromWarrantExercises_3465bfcb-3684-4747-8d33-fd35c1a0a521" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_314762e2-8248-4099-8265-597606607049" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_314762e2-8248-4099-8265-597606607049" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_d8d3c99e-a2a7-498a-ae08-cf0df4235d98" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_d8d3c99e-a2a7-498a-ae08-cf0df4235d98" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_82ad1863-380f-4cf9-bd6a-c44a303f0c1d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_82ad1863-380f-4cf9-bd6a-c44a303f0c1d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_SaleOfStockRemainingValueAuthorizedForIssuance_5f0ef1d7-24aa-4496-ba36-5239acdca7c7" xlink:href="aqst-20230630.xsd#aqst_SaleOfStockRemainingValueAuthorizedForIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_aqst_SaleOfStockRemainingValueAuthorizedForIssuance_5f0ef1d7-24aa-4496-ba36-5239acdca7c7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_7b22dad3-19f9-4e17-a860-9cf1696a7f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_ceabef2c-8d2f-4ec8-9953-9b7e2c61d635" xlink:to="loc_us-gaap_SubsequentEventTable_7b22dad3-19f9-4e17-a860-9cf1696a7f8c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_78b4b542-c678-4562-ae63-9cc87040fe6b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_7b22dad3-19f9-4e17-a860-9cf1696a7f8c" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_78b4b542-c678-4562-ae63-9cc87040fe6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_78b4b542-c678-4562-ae63-9cc87040fe6b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_78b4b542-c678-4562-ae63-9cc87040fe6b" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_78b4b542-c678-4562-ae63-9cc87040fe6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_7dd676a2-8988-4148-b408-0980902e01d6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_78b4b542-c678-4562-ae63-9cc87040fe6b" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_7dd676a2-8988-4148-b408-0980902e01d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_13c1d3df-1aac-4fdd-afac-bfc3c9e964de" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_7dd676a2-8988-4148-b408-0980902e01d6" xlink:to="loc_us-gaap_SubsequentEventMember_13c1d3df-1aac-4fdd-afac-bfc3c9e964de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_d2432591-55c6-4ed6-bd82-0c38546cd5ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_7b22dad3-19f9-4e17-a860-9cf1696a7f8c" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_d2432591-55c6-4ed6-bd82-0c38546cd5ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_d2432591-55c6-4ed6-bd82-0c38546cd5ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_d2432591-55c6-4ed6-bd82-0c38546cd5ba" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_d2432591-55c6-4ed6-bd82-0c38546cd5ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_906ce1cb-c425-40d2-91df-eaa990dcd382" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_d2432591-55c6-4ed6-bd82-0c38546cd5ba" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_906ce1cb-c425-40d2-91df-eaa990dcd382" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_AtTheMarketOfferingMember_e2938203-b146-4618-9623-d738a2c6e2c0" xlink:href="aqst-20230630.xsd#aqst_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_906ce1cb-c425-40d2-91df-eaa990dcd382" xlink:to="loc_aqst_AtTheMarketOfferingMember_e2938203-b146-4618-9623-d738a2c6e2c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_74145f52-ef63-4d11-80ed-75d8706e3771" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_7b22dad3-19f9-4e17-a860-9cf1696a7f8c" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_74145f52-ef63-4d11-80ed-75d8706e3771" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_74145f52-ef63-4d11-80ed-75d8706e3771_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_74145f52-ef63-4d11-80ed-75d8706e3771" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_74145f52-ef63-4d11-80ed-75d8706e3771_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_dcc1aed4-353a-40ee-ad43-84d9515ba16f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_74145f52-ef63-4d11-80ed-75d8706e3771" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_dcc1aed4-353a-40ee-ad43-84d9515ba16f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_ExistingWarrantsMember_01456c52-f1e0-4d78-ae2b-cdcf545e6bcd" xlink:href="aqst-20230630.xsd#aqst_ExistingWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_dcc1aed4-353a-40ee-ad43-84d9515ba16f" xlink:to="loc_aqst_ExistingWarrantsMember_01456c52-f1e0-4d78-ae2b-cdcf545e6bcd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aqst_NewWarrantsMember_4906f153-4c97-4935-b854-e55d622d7efd" xlink:href="aqst-20230630.xsd#aqst_NewWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_dcc1aed4-353a-40ee-ad43-84d9515ba16f" xlink:to="loc_aqst_NewWarrantsMember_4906f153-4c97-4935-b854-e55d622d7efd" xlink:type="arc" order="1"/>
  </link:definitionLink>
</link:linkbase>
