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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2024 Workiva-->
<!--r:ef2d3cc9-3ee3-4038-8e0e-76765ba28c91,g:61a4c83f-8a97-40b8-be4d-e910d98c8435-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:ardx="http://www.ardelyx.com/20231231" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types1="http://www.xbrl.org/dtr/type/2020-01-21" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2022-03-31" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.ardelyx.com/20231231">
  <xs:import namespace="http://fasb.org/srt/2023" schemaLocation="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2023" schemaLocation="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd"/>
  <xs:import namespace="http://www.w3.org/1999/xlink" schemaLocation="http://www.xbrl.org/2003/xlink-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2022-03-31" schemaLocation="https://www.xbrl.org/dtr/type/2022-03-31/types.xsd"/>
  <xs:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/country/2023" schemaLocation="https://xbrl.sec.gov/country/2023/country-2023.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2023" schemaLocation="https://xbrl.sec.gov/dei/2023/dei-2023.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/ecd/2023" schemaLocation="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="ardx-20231231_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="ardx-20231231_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="ardx-20231231_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="ardx-20231231_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="Cover" roleURI="http://www.ardelyx.com/role/Cover">
        <link:definition>0000001 - Document - Cover</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AuditInformation" roleURI="http://www.ardelyx.com/role/AuditInformation">
        <link:definition>0000002 - Document - Audit Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BALANCESHEETS" roleURI="http://www.ardelyx.com/role/BALANCESHEETS">
        <link:definition>0000003 - Statement - BALANCE SHEETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BALANCESHEETSParenthetical" roleURI="http://www.ardelyx.com/role/BALANCESHEETSParenthetical">
        <link:definition>0000004 - Statement - BALANCE SHEETS (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="STATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS" roleURI="http://www.ardelyx.com/role/STATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS">
        <link:definition>0000005 - Statement - STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="STATEMENTSOFSTOCKHOLDERSEQUITY" roleURI="http://www.ardelyx.com/role/STATEMENTSOFSTOCKHOLDERSEQUITY">
        <link:definition>0000006 - Statement - STATEMENTS OF STOCKHOLDERS' EQUITY</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="STATEMENTSOFCASHFLOWS" roleURI="http://www.ardelyx.com/role/STATEMENTSOFCASHFLOWS">
        <link:definition>0000007 - Statement - STATEMENTS OF CASH FLOWS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OrganizationandBasisofPresentation" roleURI="http://www.ardelyx.com/role/OrganizationandBasisofPresentation">
        <link:definition>0000008 - Disclosure - Organization and Basis of Presentation</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPolicies" roleURI="http://www.ardelyx.com/role/SummaryofSignificantAccountingPolicies">
        <link:definition>0000009 - Disclosure - Summary of Significant Accounting Policies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CashCashEquivalentsandShortTermInvestments" roleURI="http://www.ardelyx.com/role/CashCashEquivalentsandShortTermInvestments">
        <link:definition>0000010 - Disclosure - Cash, Cash Equivalents and Short-Term Investments</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurements" roleURI="http://www.ardelyx.com/role/FairValueMeasurements">
        <link:definition>0000011 - Disclosure - Fair Value Measurements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Inventory" roleURI="http://www.ardelyx.com/role/Inventory">
        <link:definition>0000012 - Disclosure - Inventory</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Revenue" roleURI="http://www.ardelyx.com/role/Revenue">
        <link:definition>0000013 - Disclosure - Revenue</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CollaborationandLicensingAgreements" roleURI="http://www.ardelyx.com/role/CollaborationandLicensingAgreements">
        <link:definition>0000014 - Disclosure - Collaboration and Licensing Agreements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DeferredRoyaltyObligationRelatedToTheSaleOfFutureRoyalties" roleURI="http://www.ardelyx.com/role/DeferredRoyaltyObligationRelatedToTheSaleOfFutureRoyalties">
        <link:definition>0000015 - Disclosure - Deferred Royalty Obligation Related To The Sale Of Future Royalties</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Borrowing" roleURI="http://www.ardelyx.com/role/Borrowing">
        <link:definition>0000016 - Disclosure - Borrowing</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativeLiabilities" roleURI="http://www.ardelyx.com/role/DerivativeLiabilities">
        <link:definition>0000017 - Disclosure - Derivative Liabilities</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Leases" roleURI="http://www.ardelyx.com/role/Leases">
        <link:definition>0000018 - Disclosure - Leases</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockholdersEquity" roleURI="http://www.ardelyx.com/role/StockholdersEquity">
        <link:definition>0000019 - Disclosure - Stockholders' Equity</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlans" roleURI="http://www.ardelyx.com/role/EquityIncentivePlans">
        <link:definition>0000020 - Disclosure - Equity Incentive Plans</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Restructuring" roleURI="http://www.ardelyx.com/role/Restructuring">
        <link:definition>0000021 - Disclosure - Restructuring</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyandEquipmentNet" roleURI="http://www.ardelyx.com/role/PropertyandEquipmentNet">
        <link:definition>0000022 - Disclosure - Property and Equipment, Net</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedExpensesandOtherCurrentLiabilities" roleURI="http://www.ardelyx.com/role/AccruedExpensesandOtherCurrentLiabilities">
        <link:definition>0000023 - Disclosure - Accrued Expenses and Other Current Liabilities</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxes" roleURI="http://www.ardelyx.com/role/IncomeTaxes">
        <link:definition>0000024 - Disclosure - Income Taxes</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GeographicInformationandConcentrations" roleURI="http://www.ardelyx.com/role/GeographicInformationandConcentrations">
        <link:definition>0000025 - Disclosure - Geographic Information and Concentrations</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NetLossPerShare" roleURI="http://www.ardelyx.com/role/NetLossPerShare">
        <link:definition>0000026 - Disclosure - Net Loss Per Share</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingencies" roleURI="http://www.ardelyx.com/role/CommitmentsandContingencies">
        <link:definition>0000027 - Disclosure - Commitments and Contingencies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesPolicies" roleURI="http://www.ardelyx.com/role/SummaryofSignificantAccountingPoliciesPolicies">
        <link:definition>9954471 - Disclosure - Summary of Significant Accounting Policies (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CashCashEquivalentsandShortTermInvestmentsTables" roleURI="http://www.ardelyx.com/role/CashCashEquivalentsandShortTermInvestmentsTables">
        <link:definition>9954472 - Disclosure - Cash, Cash Equivalents and Short-Term Investments (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsTables" roleURI="http://www.ardelyx.com/role/FairValueMeasurementsTables">
        <link:definition>9954473 - Disclosure - Fair Value Measurements (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoryTables" roleURI="http://www.ardelyx.com/role/InventoryTables">
        <link:definition>9954474 - Disclosure - Inventory (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueTables" roleURI="http://www.ardelyx.com/role/RevenueTables">
        <link:definition>9954475 - Disclosure - Revenue (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CollaborationandLicensingAgreementsTables" roleURI="http://www.ardelyx.com/role/CollaborationandLicensingAgreementsTables">
        <link:definition>9954476 - Disclosure - Collaboration and Licensing Agreements (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BorrowingTables" roleURI="http://www.ardelyx.com/role/BorrowingTables">
        <link:definition>9954477 - Disclosure - Borrowing (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativeLiabilitiesTables" roleURI="http://www.ardelyx.com/role/DerivativeLiabilitiesTables">
        <link:definition>9954478 - Disclosure - Derivative Liabilities (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesTables" roleURI="http://www.ardelyx.com/role/LeasesTables">
        <link:definition>9954479 - Disclosure - Leases (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansTables" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansTables">
        <link:definition>9954480 - Disclosure - Equity Incentive Plans (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyandEquipmentNetTables" roleURI="http://www.ardelyx.com/role/PropertyandEquipmentNetTables">
        <link:definition>9954481 - Disclosure - Property and Equipment, Net (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedExpensesandOtherCurrentLiabilitiesTables" roleURI="http://www.ardelyx.com/role/AccruedExpensesandOtherCurrentLiabilitiesTables">
        <link:definition>9954482 - Disclosure - Accrued Expenses and Other Current Liabilities (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesTables" roleURI="http://www.ardelyx.com/role/IncomeTaxesTables">
        <link:definition>9954483 - Disclosure - Income Taxes (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GeographicInformationandConcentrationsTables" roleURI="http://www.ardelyx.com/role/GeographicInformationandConcentrationsTables">
        <link:definition>9954484 - Disclosure - Geographic Information and Concentrations (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NetLossPerShareTables" roleURI="http://www.ardelyx.com/role/NetLossPerShareTables">
        <link:definition>9954485 - Disclosure - Net Loss Per Share (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OrganizationandBasisofPresentationDetails" roleURI="http://www.ardelyx.com/role/OrganizationandBasisofPresentationDetails">
        <link:definition>9954486 - Disclosure - Organization and Basis of Presentation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesLiquidityDetails" roleURI="http://www.ardelyx.com/role/SummaryofSignificantAccountingPoliciesLiquidityDetails">
        <link:definition>9954487 - Disclosure - Summary of Significant Accounting Policies - Liquidity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesAccountsReceivableDetails" roleURI="http://www.ardelyx.com/role/SummaryofSignificantAccountingPoliciesAccountsReceivableDetails">
        <link:definition>9954488 - Disclosure - Summary of Significant Accounting Policies - Accounts Receivable (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesNarrativeDetails" roleURI="http://www.ardelyx.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails">
        <link:definition>9954489 - Disclosure - Summary of Significant Accounting Policies - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CashCashEquivalentsandShortTermInvestmentsSecuritiesClassifiedasCashandShortTermInvestmentsDetails" roleURI="http://www.ardelyx.com/role/CashCashEquivalentsandShortTermInvestmentsSecuritiesClassifiedasCashandShortTermInvestmentsDetails">
        <link:definition>9954490 - Disclosure - Cash, Cash Equivalents and Short-Term Investments - Securities Classified as Cash and Short-Term Investments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CashCashEquivalentsandShortTermInvestmentsSecuritiesClassifiedasCashandShortTermInvestmentsDetails_1" roleURI="http://www.ardelyx.com/role/CashCashEquivalentsandShortTermInvestmentsSecuritiesClassifiedasCashandShortTermInvestmentsDetails_1">
        <link:definition>9954490 - Disclosure - Cash, Cash Equivalents and Short-Term Investments - Securities Classified as Cash and Short-Term Investments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CashCashEquivalentsandShortTermInvestmentsNarrativeDetails" roleURI="http://www.ardelyx.com/role/CashCashEquivalentsandShortTermInvestmentsNarrativeDetails">
        <link:definition>9954491 - Disclosure - Cash, Cash Equivalents and Short-Term Investments - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredonaRecurringBasisDetails" roleURI="http://www.ardelyx.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredonaRecurringBasisDetails">
        <link:definition>9954492 - Disclosure - Fair Value Measurements - Financial Assets and Liabilities Measured on a Recurring Basis (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsNarrativeDetails" roleURI="http://www.ardelyx.com/role/FairValueMeasurementsNarrativeDetails">
        <link:definition>9954493 - Disclosure - Fair Value Measurements - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoryScheduleDetails" roleURI="http://www.ardelyx.com/role/InventoryScheduleDetails">
        <link:definition>9954494 - Disclosure - Inventory - Schedule (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoryNarrativeDetails" roleURI="http://www.ardelyx.com/role/InventoryNarrativeDetails">
        <link:definition>9954495 - Disclosure - Inventory - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueScheduleofRevenueDetails" roleURI="http://www.ardelyx.com/role/RevenueScheduleofRevenueDetails">
        <link:definition>9954496 - Disclosure - Revenue - Schedule of Revenue (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueRevenuefromCustomersasaPercentageofTotalProductRevenueNetDetails" roleURI="http://www.ardelyx.com/role/RevenueRevenuefromCustomersasaPercentageofTotalProductRevenueNetDetails">
        <link:definition>9954497 - Disclosure - Revenue - Revenue from Customers as a Percentage of Total Product Revenue, Net (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueGrosstoNetSalesAccrualsDetails" roleURI="http://www.ardelyx.com/role/RevenueGrosstoNetSalesAccrualsDetails">
        <link:definition>9954498 - Disclosure - Revenue - Gross-to-Net Sales Accruals (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CollaborationandLicensingAgreementsNarrativeDetails" roleURI="http://www.ardelyx.com/role/CollaborationandLicensingAgreementsNarrativeDetails">
        <link:definition>9954499 - Disclosure - Collaboration and Licensing Agreements - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CollaborationandLicensingAgreementsDeferredRevenueDetails" roleURI="http://www.ardelyx.com/role/CollaborationandLicensingAgreementsDeferredRevenueDetails">
        <link:definition>9954500 - Disclosure - Collaboration and Licensing Agreements - Deferred Revenue (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DeferredRoyaltyObligationRelatedToTheSaleOfFutureRoyaltiesDetails" roleURI="http://www.ardelyx.com/role/DeferredRoyaltyObligationRelatedToTheSaleOfFutureRoyaltiesDetails">
        <link:definition>9954501 - Disclosure - Deferred Royalty Obligation Related To The Sale Of Future Royalties (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BorrowingNarrativeDetails" roleURI="http://www.ardelyx.com/role/BorrowingNarrativeDetails">
        <link:definition>9954502 - Disclosure - Borrowing - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BorrowingFuturePaymentObligationsDetails" roleURI="http://www.ardelyx.com/role/BorrowingFuturePaymentObligationsDetails">
        <link:definition>9954503 - Disclosure - Borrowing - Future Payment Obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BorrowingFuturePaymentObligationsDetails_1" roleURI="http://www.ardelyx.com/role/BorrowingFuturePaymentObligationsDetails_1">
        <link:definition>9954503 - Disclosure - Borrowing - Future Payment Obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativeLiabilitiesNarrativeDetails" roleURI="http://www.ardelyx.com/role/DerivativeLiabilitiesNarrativeDetails">
        <link:definition>9954504 - Disclosure - Derivative Liabilities - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativeLiabilitiesChangesinFairValueDetails" roleURI="http://www.ardelyx.com/role/DerivativeLiabilitiesChangesinFairValueDetails">
        <link:definition>9954505 - Disclosure - Derivative Liabilities - Changes in Fair Value (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesNarrativeDetails" roleURI="http://www.ardelyx.com/role/LeasesNarrativeDetails">
        <link:definition>9954506 - Disclosure - Leases - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesAdditionalLeaseInformationDetails" roleURI="http://www.ardelyx.com/role/LeasesAdditionalLeaseInformationDetails">
        <link:definition>9954507 - Disclosure - Leases - Additional Lease Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesLeaseCostsDetails" roleURI="http://www.ardelyx.com/role/LeasesLeaseCostsDetails">
        <link:definition>9954508 - Disclosure - Leases - Lease Costs (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesUndiscountedCashPaymentObligationsDetails" roleURI="http://www.ardelyx.com/role/LeasesUndiscountedCashPaymentObligationsDetails">
        <link:definition>9954509 - Disclosure - Leases - Undiscounted Cash Payment Obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesUndiscountedCashPaymentObligationsDetails_1" roleURI="http://www.ardelyx.com/role/LeasesUndiscountedCashPaymentObligationsDetails_1">
        <link:definition>9954509 - Disclosure - Leases - Undiscounted Cash Payment Obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockholdersEquityDetails" roleURI="http://www.ardelyx.com/role/StockholdersEquityDetails">
        <link:definition>9954510 - Disclosure - Stockholders' Equity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansNarrativeDetails" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansNarrativeDetails">
        <link:definition>9954511 - Disclosure - Equity Incentive Plans - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansStockOptionsDetails" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansStockOptionsDetails">
        <link:definition>9954512 - Disclosure - Equity Incentive Plans - Stock Options (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansValuationAssumptionsforStockOptionsDetails" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansValuationAssumptionsforStockOptionsDetails">
        <link:definition>9954513 - Disclosure - Equity Incentive Plans - Valuation Assumptions for Stock Options (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansRestrictedStockUnitsDetails" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansRestrictedStockUnitsDetails">
        <link:definition>9954514 - Disclosure - Equity Incentive Plans - Restricted Stock Units (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansValuationAssumptionsforESPPDetails" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansValuationAssumptionsforESPPDetails">
        <link:definition>9954515 - Disclosure - Equity Incentive Plans - Valuation Assumptions for ESPP (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansStockBasedCompensationDetails" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansStockBasedCompensationDetails">
        <link:definition>9954516 - Disclosure - Equity Incentive Plans - Stock-Based Compensation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityIncentivePlansUnrecognizedStockBasedCompensationDetails" roleURI="http://www.ardelyx.com/role/EquityIncentivePlansUnrecognizedStockBasedCompensationDetails">
        <link:definition>9954517 - Disclosure - Equity Incentive Plans - Unrecognized Stock-Based Compensation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RestructuringDetails" roleURI="http://www.ardelyx.com/role/RestructuringDetails">
        <link:definition>9954518 - Disclosure - Restructuring (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyandEquipmentNetBalancesDetails" roleURI="http://www.ardelyx.com/role/PropertyandEquipmentNetBalancesDetails">
        <link:definition>9954519 - Disclosure - Property and Equipment, Net - Balances (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyandEquipmentNetNarrativeDetails" roleURI="http://www.ardelyx.com/role/PropertyandEquipmentNetNarrativeDetails">
        <link:definition>9954520 - Disclosure - Property and Equipment, Net - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedExpensesandOtherCurrentLiabilitiesDetails" roleURI="http://www.ardelyx.com/role/AccruedExpensesandOtherCurrentLiabilitiesDetails">
        <link:definition>9954521 - Disclosure - Accrued Expenses and Other Current Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesComponentsofProvisionforIncomeTaxesDetails" roleURI="http://www.ardelyx.com/role/IncomeTaxesComponentsofProvisionforIncomeTaxesDetails">
        <link:definition>9954522 - Disclosure - Income Taxes - Components of Provision for Income Taxes (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesReconciliationofEffectiveTaxRateDetails" roleURI="http://www.ardelyx.com/role/IncomeTaxesReconciliationofEffectiveTaxRateDetails">
        <link:definition>9954523 - Disclosure - Income Taxes - Reconciliation of Effective Tax Rate (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesComponentsofDeferredTaxAssetsDetails" roleURI="http://www.ardelyx.com/role/IncomeTaxesComponentsofDeferredTaxAssetsDetails">
        <link:definition>9954524 - Disclosure - Income Taxes - Components of Deferred Tax Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesNarrativeDetails" roleURI="http://www.ardelyx.com/role/IncomeTaxesNarrativeDetails">
        <link:definition>9954525 - Disclosure - Income Taxes - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesReconciliationofUnrecognizedTaxBenefitsDetails" roleURI="http://www.ardelyx.com/role/IncomeTaxesReconciliationofUnrecognizedTaxBenefitsDetails">
        <link:definition>9954526 - Disclosure - Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GeographicInformationandConcentrationsRevenuebyGeographicalAreaDetails" roleURI="http://www.ardelyx.com/role/GeographicInformationandConcentrationsRevenuebyGeographicalAreaDetails">
        <link:definition>9954527 - Disclosure - Geographic Information and Concentrations - Revenue by Geographical Area (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GeographicInformationandConcentrationsConcentrationRiskDetails" roleURI="http://www.ardelyx.com/role/GeographicInformationandConcentrationsConcentrationRiskDetails">
        <link:definition>9954528 - Disclosure - Geographic Information and Concentrations - Concentration Risk (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NetLossPerShareComputationofNetLossPerCommonShareDetails" roleURI="http://www.ardelyx.com/role/NetLossPerShareComputationofNetLossPerCommonShareDetails">
        <link:definition>9954529 - Disclosure - Net Loss Per Share - Computation of Net Loss Per Common Share (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NetLossPerShareAntiDilutiveSecuritiesandPotentialCommonSharesDetails" roleURI="http://www.ardelyx.com/role/NetLossPerShareAntiDilutiveSecuritiesandPotentialCommonSharesDetails">
        <link:definition>9954530 - Disclosure - Net Loss Per Share - Anti-Dilutive Securities and Potential Common Shares (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingenciesDetails" roleURI="http://www.ardelyx.com/role/CommitmentsandContingenciesDetails">
        <link:definition>9954531 - Disclosure - Commitments and Contingencies (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueRecognizedCashNotReceivedNoncurrent" abstract="false" name="ContractWithCustomerLiabilityRevenueRecognizedCashNotReceivedNoncurrent" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ExitFee2018Member" abstract="true" name="ExitFee2018Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToCreditsOrDeductionsIssued" abstract="false" name="ContractWithCustomerGrossToCreditsOrDeductionsIssued" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_OfficeEquipmentAndFurnitureMember" abstract="true" name="OfficeEquipmentAndFurnitureMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_PercentageOfNonRoyaltyRevenue" abstract="false" name="PercentageOfNonRoyaltyRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerCopayAndReturnsMember" abstract="true" name="ContractWithCustomerCopayAndReturnsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_AccruedGrossToNetRevenueLiabilities" abstract="false" name="AccruedGrossToNetRevenueLiabilities" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborationPartnershipConcentrationRiskMember" abstract="true" name="CollaborationPartnershipConcentrationRiskMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInChinaMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInChinaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_OpenMarketSalesAgreement2023AtTheMarketOfferingMember" abstract="true" name="OpenMarketSalesAgreement2023AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityDecreaseInRevenueToBeRecognizedInNextTwelveMonths" abstract="false" name="ContractWithCustomerLiabilityDecreaseInRevenueToBeRecognizedInNextTwelveMonths" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_MinimumTaxCreditCarryforwardMember" abstract="true" name="MinimumTaxCreditCarryforwardMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LesseeOperatingLeaseLiabilityToBePaidAfterYearThree" abstract="false" name="LesseeOperatingLeaseLiabilityToBePaidAfterYearThree" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PotentialCommonSharesAntiDilutiveEffectOnSecurities" abstract="false" name="PotentialCommonSharesAntiDilutiveEffectOnSecurities" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_EmployeeStockPurchasePlanMember" abstract="true" name="EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_TwoThousandSixteenEmploymentCommencementIncentivePlanMember" abstract="true" name="TwoThousandSixteenEmploymentCommencementIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LineOfCreditFacilityAccordionFeatureAdditionalCommittedCapital" abstract="false" name="LineOfCreditFacilityAccordionFeatureAdditionalCommittedCapital" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AccruedNonClinicalResearchAndDevelopmentExpenses" abstract="false" name="AccruedNonClinicalResearchAndDevelopmentExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LongTermDebtMaturityAfterYearFour" abstract="false" name="LongTermDebtMaturityAfterYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DebtInstrumentInterestRateOnDefaultPercentage" abstract="false" name="DebtInstrumentInterestRateOnDefaultPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponExerciseOfStockOptions" abstract="false" name="IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponExerciseOfStockOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialDevelopmentAndCommercializationMilestones" abstract="false" name="CollaborativeArrangementPotentialDevelopmentAndCommercializationMilestones" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ProceedsFromSaleOfFutureRoyaltiesNetOfIssuanceCosts" abstract="false" name="ProceedsFromSaleOfFutureRoyaltiesNetOfIssuanceCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_OpenMarketSalesAgreement2020AtTheMarketOfferingMember" abstract="true" name="OpenMarketSalesAgreement2020AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_SubleaseFacilityFremontCaliforniaMember" abstract="true" name="SubleaseFacilityFremontCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_GeographicInformationAndConcentrationsTextBlock" abstract="false" name="GeographicInformationAndConcentrationsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="ardx_GrossToNetSalesAccrualAndReserveClassificationDomain" abstract="true" name="GrossToNetSalesAccrualAndReserveClassificationDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_GrossToNetSalesAccrualAndReserveClassificationAxis" abstract="true" name="GrossToNetSalesAccrualAndReserveClassificationAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_NonCashInterestExpenseOnDeferredRoyaltyObligationPolicyTextBlock" abstract="false" name="NonCashInterestExpenseOnDeferredRoyaltyObligationPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="ardx_TaxAuthorityStatesOtherThanCaliforniaMember" abstract="true" name="TaxAuthorityStatesOtherThanCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialDevelopmentMilestones" abstract="false" name="CollaborativeArrangementPotentialDevelopmentMilestones" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_SecuredOvernightFinancingRateSOFRMember" abstract="true" name="SecuredOvernightFinancingRateSOFRMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialCommercializationMilestones" abstract="false" name="CollaborativeArrangementPotentialCommercializationMilestones" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityAmortizationEffectiveInterestRatePercent" abstract="false" name="ContractWithCustomerLiabilityAmortizationEffectiveInterestRatePercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_ISBRELAAndXPHOZAHUnitsPreviouslyExpensedInPeriodPriorToCommencementOfCapitalizationOfInventoryCostsMember" abstract="true" name="ISBRELAAndXPHOZAHUnitsPreviouslyExpensedInPeriodPriorToCommencementOfCapitalizationOfInventoryCostsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CostOfRevenueAggregateAmountRecognized" abstract="false" name="CostOfRevenueAggregateAmountRecognized" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_TermLoan2022CMember" abstract="true" name="TermLoan2022CMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DerivativeLiabilityForExitFees" abstract="false" name="DerivativeLiabilityForExitFees" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ChangeInContractWithCustomerLiabilityCurrentRollforwardRollForward" abstract="true" name="ChangeInContractWithCustomerLiabilityCurrentRollforwardRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_OpenMarketSalesAgreement2021AtTheMarketOfferingMember" abstract="true" name="OpenMarketSalesAgreement2021AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsAbstract" abstract="true" name="CollaborationAndLicensingAgreementsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ExitFeePercentage" abstract="false" name="ExitFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_PrepaidCommercialManufacturingNonCurrent" abstract="false" name="PrepaidCommercialManufacturingNonCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborativeDevelopmentMember" abstract="true" name="CollaborativeDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_DeferredRoyaltyObligationNoncurrent" abstract="false" name="DeferredRoyaltyObligationNoncurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ProductIBSRELAMember" abstract="true" name="ProductIBSRELAMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LoanAgreementExitFeeTerm" abstract="false" name="LoanAgreementExitFeeTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_AccruedExpensesPolicyPolicyTextBlock" abstract="false" name="AccruedExpensesPolicyPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_ThresholdPercentageOfSalesForTieredRoyalties" abstract="false" name="ThresholdPercentageOfSalesForTieredRoyalties" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_CollaborativeArrangementFeeReceivableForReductionInRoyaltyRateNumberOfPaymentTranches" abstract="false" name="CollaborativeArrangementFeeReceivableForReductionInRoyaltyRateNumberOfPaymentTranches" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_OfficerTradingArrangementMember" abstract="true" name="OfficerTradingArrangementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_TwoThousandEightStockIncentivePlanMember" abstract="true" name="TwoThousandEightStockIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_DebtInstrumentPrepaymentFeePercentage" abstract="false" name="DebtInstrumentPrepaymentFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_DebtInstrumentFeeDueUponMaturityAccelerationPrepaymentTerminationPercentage" abstract="false" name="DebtInstrumentFeeDueUponMaturityAccelerationPrepaymentTerminationPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_AccruedSalesAndMarketingExpenses" abstract="false" name="AccruedSalesAndMarketingExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AstrazenecaMember" abstract="true" name="AstrazenecaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_RevenueRemainingPerformanceObligationVariableConsiderationAmount" abstract="false" name="RevenueRemainingPerformanceObligationVariableConsiderationAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AuditInformationAbstract" abstract="true" name="AuditInformationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ContractWithCustomerRebatesWholesalerAndGPOFeesMember" abstract="true" name="ContractWithCustomerRebatesWholesalerAndGPOFeesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_ShortTermInvestmentsPolicyTextBlock" abstract="false" name="ShortTermInvestmentsPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueInvoicedAsPrepaymentsForProductSupplyCurrent" abstract="false" name="ContractWithCustomerLiabilityRevenueInvoicedAsPrepaymentsForProductSupplyCurrent" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AstraZenecaTerminationAgreementMember" abstract="true" name="AstraZenecaTerminationAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_FacilityMilwaukeeWisconsinMember" abstract="true" name="FacilityMilwaukeeWisconsinMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_DeferredTaxLiabilitiesRightOfUseAsset" abstract="false" name="DeferredTaxLiabilitiesRightOfUseAsset" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_TermLoan2018Member" abstract="true" name="TermLoan2018Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_NumberOfOperatingLeaseArrangements" abstract="false" name="NumberOfOperatingLeaseArrangements" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_CommonStockSubjectToIssuedInducementGrantsShares" abstract="false" name="CommonStockSubjectToIssuedInducementGrantsShares" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_LauraWilliamsMember" abstract="true" name="LauraWilliamsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AccruedPaymentsDueToThirdParty" abstract="false" name="AccruedPaymentsDueToThirdParty" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_HealthCareRoyaltyPartnersIVLPMember" abstract="true" name="HealthCareRoyaltyPartnersIVLPMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LineOfCreditFacilityAccordionFeatureAdditionalUncommittedCapital" abstract="false" name="LineOfCreditFacilityAccordionFeatureAdditionalUncommittedCapital" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesUnderEmployeeStockPurchasePlan" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesUnderEmployeeStockPurchasePlan" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_AccruedContractManufacturingCosts" abstract="false" name="AccruedContractManufacturingCosts" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AccountsReceivableCommercialCustomerMember" abstract="true" name="AccountsReceivableCommercialCustomerMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_StockOptionsAggregateIntrinsicValueAbstract" abstract="true" name="StockOptionsAggregateIntrinsicValueAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_StrezsakVersusArdelyxIncMember" abstract="true" name="StrezsakVersusArdelyxIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LoanAgreementExitFeeNetProductRevenueThresholdMetricTrailingSixMonthBasisMinimum" abstract="false" name="LoanAgreementExitFeeNetProductRevenueThresholdMetricTrailingSixMonthBasisMinimum" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_KyowaKirinCo.LtdMember" abstract="true" name="KyowaKirinCo.LtdMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceMinimum" abstract="false" name="LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceMinimum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesAccruals" abstract="false" name="ContractWithCustomerGrossToNetSalesAccruals" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CashCashEquivalentsAndInvestmentsGrossUnrealizedGains" abstract="false" name="CashCashEquivalentsAndInvestmentsGrossUnrealizedGains" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LaboratoryEquipmentMember" abstract="true" name="LaboratoryEquipmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_PercentageOfRoyaltyRevenue" abstract="false" name="PercentageOfRoyaltyRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_FacilityFremontCaliforniaMember" abstract="true" name="FacilityFremontCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_AccruedClinicalExpenses" abstract="false" name="AccruedClinicalExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_TermLoan2022DMember" abstract="true" name="TermLoan2022DMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_RobertBlanksMember" abstract="true" name="RobertBlanksMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_GoVersusRaabMember" abstract="true" name="GoVersusRaabMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponInclusionOfForfeitedOrUnexercisedOptions" abstract="false" name="IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponInclusionOfForfeitedOrUnexercisedOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_CashCashEquivalentsAndInvestmentsGrossUnrealizedLosses" abstract="false" name="CashCashEquivalentsAndInvestmentsGrossUnrealizedLosses" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueInvoicedAsPrepaymentsForProductSupplyNoncurrent" abstract="false" name="ContractWithCustomerLiabilityRevenueInvoicedAsPrepaymentsForProductSupplyNoncurrent" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AccruedProfessionalAndConsultantFeesCurrent" abstract="false" name="AccruedProfessionalAndConsultantFeesCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesAccrualRollForward" abstract="true" name="ContractWithCustomerGrossToNetSalesAccrualRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_IncreaseDecreaseInPrepaidCommercialManufacturingExpense" abstract="false" name="IncreaseDecreaseInPrepaidCommercialManufacturingExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityTransactionCosts" abstract="false" name="ContractWithCustomerLiabilityTransactionCosts" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ProductSupplyRevenueMember" abstract="true" name="ProductSupplyRevenueMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_TermLoan2022AMember" abstract="true" name="TermLoan2022AMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_DeferredTaxAssetsAmortizationAndDepreciation" abstract="false" name="DeferredTaxAssetsAmortizationAndDepreciation" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AmerisourceBergenDrugCorporationMember" abstract="true" name="AmerisourceBergenDrugCorporationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_InvestmentsAndCashAmortizedCost" abstract="false" name="InvestmentsAndCashAmortizedCost" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueToBeRecognizedInNextTwelveMonths" abstract="false" name="ContractWithCustomerLiabilityRevenueToBeRecognizedInNextTwelveMonths" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DebtInstrumentClosingFeeAmount" abstract="false" name="DebtInstrumentClosingFeeAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" abstract="false" name="FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_SaleOfStockWeightedAveragePricePerShare" abstract="false" name="SaleOfStockWeightedAveragePricePerShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="ardx_TermLoan2022BMember" abstract="true" name="TermLoan2022BMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_LoanAgreementFutureObligationUponFundingOrOtherEvents" abstract="false" name="LoanAgreementFutureObligationUponFundingOrOtherEvents" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesMaximum" abstract="false" name="AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesMaximum" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_EffectiveIncomeTaxRateReconciliationForeignWithholdingTaxPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationForeignWithholdingTaxPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_BioridgePhamaMember" abstract="true" name="BioridgePhamaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AccountsReceivableCollaboratorMember" abstract="true" name="AccountsReceivableCollaboratorMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_ExitFee2022Member" abstract="true" name="ExitFee2022Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialPaymentPerTerminationAgreementMaximum" abstract="false" name="CollaborativeArrangementPotentialPaymentPerTerminationAgreementMaximum" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CardinalHealthMember" abstract="true" name="CardinalHealthMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceOptionForAnnualIncreaseAsPercentageOfSharesOutstanding" abstract="false" name="IncreaseInSharesReservedForIssuanceOptionForAnnualIncreaseAsPercentageOfSharesOutstanding" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_McKessonCorporationMember" abstract="true" name="McKessonCorporationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_MichaelRaabMember" abstract="true" name="MichaelRaabMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ChangeInContractWithCustomerLiabilityNoncurrentRollforwardRollForward" abstract="true" name="ChangeInContractWithCustomerLiabilityNoncurrentRollforwardRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ProductXPHOZAHMember" abstract="true" name="ProductXPHOZAHMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_TermLoan2022Member" abstract="true" name="TermLoan2022Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesProvisions" abstract="false" name="ContractWithCustomerGrossToNetSalesProvisions" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_SecuredOvernightFinancingRateSOFRFloorRateMember" abstract="true" name="SecuredOvernightFinancingRateSOFRFloorRateMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_PrepaidCommercialManufacturing" abstract="false" name="PrepaidCommercialManufacturing" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_KnightTherapeuticsIncMember" abstract="true" name="KnightTherapeuticsIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_IncomeTaxDisclosureTable" abstract="true" name="IncomeTaxDisclosureTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceCalculationPeriod" abstract="false" name="LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceCalculationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_LeaseArrangementsDomain" abstract="true" name="LeaseArrangementsDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_TwoThousandFourteenEquityIncentiveAwardPlanMember" abstract="true" name="TwoThousandFourteenEquityIncentiveAwardPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_MaximumAggregateOfferingPrice" abstract="false" name="MaximumAggregateOfferingPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_EquitySalesAgreementProceedsFromSharesIssuedSinceInception" abstract="false" name="EquitySalesAgreementProceedsFromSharesIssuedSinceInception" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_METiSTherapeuticsIncMember" abstract="true" name="METiSTherapeuticsIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LesseeOperatingLeaseNumberOfRenewalOptions" abstract="false" name="LesseeOperatingLeaseNumberOfRenewalOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_StockIssuanceCostCommissionPercent" abstract="false" name="StockIssuanceCostCommissionPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_ElizabethGrammerMember" abstract="true" name="ElizabethGrammerMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborativeArrangementFeeReceivableForReductionInRoyaltyRate" abstract="false" name="CollaborativeArrangementFeeReceivableForReductionInRoyaltyRate" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_RemainingFundingBasedOnConditionalMilestoneAchievement" abstract="false" name="RemainingFundingBasedOnConditionalMilestoneAchievement" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" abstract="true" name="ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_IncomeTaxDisclosureLineItems" abstract="true" name="IncomeTaxDisclosureLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_PrepaidCommercialManufacturingCurrent" abstract="false" name="PrepaidCommercialManufacturingCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerDiscountsAndChargebacksMember" abstract="true" name="ContractWithCustomerDiscountsAndChargebacksMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_BioRidgePharmaLLCMember" abstract="true" name="BioRidgePharmaLLCMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueRecognizedCashNotReceivedCurrent" abstract="false" name="ContractWithCustomerLiabilityRevenueRecognizedCashNotReceivedCurrent" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DerivativeIssued" abstract="false" name="DerivativeIssued" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_FacilityTwoWalthamMassachusettsMember" abstract="true" name="FacilityTwoWalthamMassachusettsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_KkcMember" abstract="true" name="KkcMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_DeferredTaxAssetsRoyaltyObligation" abstract="false" name="DeferredTaxAssetsRoyaltyObligation" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsUpfrontLicenseFees" abstract="false" name="CollaborationAndLicensingAgreementsUpfrontLicenseFees" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" abstract="false" name="LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" abstract="false" name="ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="ardx_EffectiveIncomeTaxRateReconciliationTaxExpenseBenefitExecutiveCompensationDisallowedIRCSec162mPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationTaxExpenseBenefitExecutiveCompensationDisallowedIRCSec162mPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_OperatingLossCarryforwardsWithoutExpiration" abstract="false" name="OperatingLossCarryforwardsWithoutExpiration" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ScheduleOfGrossToNetSalesAccrualsTableTextBlock" abstract="false" name="ScheduleOfGrossToNetSalesAccrualsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="ardx_LeaseArrangementsAxis" abstract="true" name="LeaseArrangementsAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_WalthamMassachusettsMember" abstract="true" name="WalthamMassachusettsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_StockOptionsWeightedAverageRemainingContractualTermAbstract" abstract="true" name="StockOptionsWeightedAverageRemainingContractualTermAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
</xs:schema>
