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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e4bdf-17e4-7a12-a6fd-1670d5d1bbd7,g:b4dcec2a-429c-42b6-a84f-cf5acda9bcb8-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:mrk="http://www.merck.com/20260630" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2024-01-31" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.merck.com/20260630">
  <xs:import namespace="http://fasb.org/srt/2026" schemaLocation="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2026" schemaLocation="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.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/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/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/2026" schemaLocation="https://xbrl.sec.gov/country/2026/country-2026.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2026" schemaLocation="https://xbrl.sec.gov/dei/2026/dei-2026.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/ecd/2026" schemaLocation="https://xbrl.sec.gov/ecd/2026/ecd-2026.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="mrk-20260630_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="mrk-20260630_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="mrk-20260630_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="mrk-20260630_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="CoverPage" roleURI="http://www.merck.com/role/CoverPage">
        <link:definition>0000001 - Document - Cover Page</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="CONDENSEDCONSOLIDATEDSTATEMENTOFOPERATIONS" roleURI="http://www.merck.com/role/CONDENSEDCONSOLIDATEDSTATEMENTOFOPERATIONS">
        <link:definition>9952151 - Statement - CONDENSED CONSOLIDATED STATEMENT OF OPERATIONS</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="CONDENSEDCONSOLIDATEDSTATEMENTOFCOMPREHENSIVELOSSINCOME" roleURI="http://www.merck.com/role/CONDENSEDCONSOLIDATEDSTATEMENTOFCOMPREHENSIVELOSSINCOME">
        <link:definition>9952152 - Statement - CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE (LOSS) INCOME</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="CONDENSEDCONSOLIDATEDBALANCESHEET" roleURI="http://www.merck.com/role/CONDENSEDCONSOLIDATEDBALANCESHEET">
        <link:definition>9952153 - Statement - CONDENSED CONSOLIDATED BALANCE SHEET</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="CONDENSEDCONSOLIDATEDBALANCESHEETParenthetical" roleURI="http://www.merck.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETParenthetical">
        <link:definition>9952154 - Statement - CONDENSED CONSOLIDATED BALANCE SHEET (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="CONDENSEDCONSOLIDATEDSTATEMENTOFCASHFLOWS" roleURI="http://www.merck.com/role/CONDENSEDCONSOLIDATEDSTATEMENTOFCASHFLOWS">
        <link:definition>9952155 - Statement - CONDENSED CONSOLIDATED STATEMENT 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="CONDENSEDCONSOLIDATEDSTATEMENTOFCASHFLOWSParenthetical" roleURI="http://www.merck.com/role/CONDENSEDCONSOLIDATEDSTATEMENTOFCASHFLOWSParenthetical">
        <link:definition>9952156 - Statement - CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (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="BasisofPresentation" roleURI="http://www.merck.com/role/BasisofPresentation">
        <link:definition>9952157 - Disclosure - 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="AcquisitionsResearchCollaborationsandLicensingAgreements" roleURI="http://www.merck.com/role/AcquisitionsResearchCollaborationsandLicensingAgreements">
        <link:definition>9952158 - Disclosure - Acquisitions, Research Collaborations 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="CollaborativeArrangements" roleURI="http://www.merck.com/role/CollaborativeArrangements">
        <link:definition>9952159 - Disclosure - Collaborative Arrangements</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.merck.com/role/Restructuring">
        <link:definition>9952160 - 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="FinancialInstruments" roleURI="http://www.merck.com/role/FinancialInstruments">
        <link:definition>9952161 - Disclosure - Financial Instruments</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="Inventories" roleURI="http://www.merck.com/role/Inventories">
        <link:definition>9952162 - Disclosure - Inventories</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="LoansPayableandLongTermDebt" roleURI="http://www.merck.com/role/LoansPayableandLongTermDebt">
        <link:definition>9952163 - Disclosure - Loans Payable and Long-Term Debt</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="Contingencies" roleURI="http://www.merck.com/role/Contingencies">
        <link:definition>9952164 - Disclosure - 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="Equity" roleURI="http://www.merck.com/role/Equity">
        <link:definition>9952165 - Disclosure - 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="PensionandOtherPostretirementBenefitPlans" roleURI="http://www.merck.com/role/PensionandOtherPostretirementBenefitPlans">
        <link:definition>9952166 - Disclosure - Pension and Other Postretirement Benefit 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="OtherIncomeExpenseNet" roleURI="http://www.merck.com/role/OtherIncomeExpenseNet">
        <link:definition>9952167 - Disclosure - Other (Income) Expense, 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="IncomeTaxes" roleURI="http://www.merck.com/role/IncomeTaxes">
        <link:definition>9952168 - 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="LossEarningsPerShare" roleURI="http://www.merck.com/role/LossEarningsPerShare">
        <link:definition>9952169 - Disclosure - (Loss) Earnings 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="OtherComprehensiveIncomeLoss" roleURI="http://www.merck.com/role/OtherComprehensiveIncomeLoss">
        <link:definition>9952170 - Disclosure - Other Comprehensive Income (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="SegmentReporting" roleURI="http://www.merck.com/role/SegmentReporting">
        <link:definition>9952171 - Disclosure - Segment Reporting</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="BasisofPresentationPolicies" roleURI="http://www.merck.com/role/BasisofPresentationPolicies">
        <link:definition>9955511 - Disclosure - Basis of Presentation (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="CollaborativeArrangementsTables" roleURI="http://www.merck.com/role/CollaborativeArrangementsTables">
        <link:definition>9955512 - Disclosure - Collaborative Arrangements (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="RestructuringTables" roleURI="http://www.merck.com/role/RestructuringTables">
        <link:definition>9955513 - Disclosure - Restructuring (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="FinancialInstrumentsTables" roleURI="http://www.merck.com/role/FinancialInstrumentsTables">
        <link:definition>9955514 - Disclosure - Financial Instruments (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="InventoriesTables" roleURI="http://www.merck.com/role/InventoriesTables">
        <link:definition>9955515 - Disclosure - Inventories (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="EquityTables" roleURI="http://www.merck.com/role/EquityTables">
        <link:definition>9955516 - Disclosure - Equity (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="PensionandOtherPostretirementBenefitPlansTables" roleURI="http://www.merck.com/role/PensionandOtherPostretirementBenefitPlansTables">
        <link:definition>9955517 - Disclosure - Pension and Other Postretirement Benefit 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="OtherIncomeExpenseNetTables" roleURI="http://www.merck.com/role/OtherIncomeExpenseNetTables">
        <link:definition>9955518 - Disclosure - Other (Income) Expense, 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="LossEarningsPerShareTables" roleURI="http://www.merck.com/role/LossEarningsPerShareTables">
        <link:definition>9955519 - Disclosure - (Loss) Earnings 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="OtherComprehensiveIncomeLossTables" roleURI="http://www.merck.com/role/OtherComprehensiveIncomeLossTables">
        <link:definition>9955520 - Disclosure - Other Comprehensive Income (Loss) (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="SegmentReportingTables" roleURI="http://www.merck.com/role/SegmentReportingTables">
        <link:definition>9955521 - Disclosure - Segment Reporting (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="AcquisitionsResearchCollaborationsandLicensingAgreementsDetails" roleURI="http://www.merck.com/role/AcquisitionsResearchCollaborationsandLicensingAgreementsDetails">
        <link:definition>9955522 - Disclosure - Acquisitions, Research Collaborations and Licensing Agreements (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="CollaborativeArrangementsAstraZenecaPLCNarrativeDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsAstraZenecaPLCNarrativeDetails">
        <link:definition>9955523 - Disclosure - Collaborative Arrangements - AstraZeneca PLC - 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="CollaborativeArrangementsAstraZenecaPLCDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsAstraZenecaPLCDetails">
        <link:definition>9955524 - Disclosure - Collaborative Arrangements - AstraZeneca PLC (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="CollaborativeArrangementsEisaiCoLtdNarrativeDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsEisaiCoLtdNarrativeDetails">
        <link:definition>9955525 - Disclosure - Collaborative Arrangements - Eisai Co., Ltd. - 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="CollaborativeArrangementsEisaiCoLtdDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsEisaiCoLtdDetails">
        <link:definition>9955526 - Disclosure - Collaborative Arrangements - Eisai Co., Ltd. (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="CollaborativeArrangementsBayerAGNarrativeDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsBayerAGNarrativeDetails">
        <link:definition>9955527 - Disclosure - Collaborative Arrangements - Bayer AG - 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="CollaborativeArrangementsBayerAGDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsBayerAGDetails">
        <link:definition>9955528 - Disclosure - Collaborative Arrangements - Bayer AG (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="CollaborativeArrangementsRidgebackBiotherapeuticsLPDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsRidgebackBiotherapeuticsLPDetails">
        <link:definition>9955529 - Disclosure - Collaborative Arrangements - Ridgeback Biotherapeutics LP (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="CollaborativeArrangementsDaiichoSankyoNarrativeDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsDaiichoSankyoNarrativeDetails">
        <link:definition>9955530 - Disclosure - Collaborative Arrangements - Daiicho Sankyo - 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="CollaborativeArrangementsScheduleofDaiichoSankyoDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsScheduleofDaiichoSankyoDetails">
        <link:definition>9955531 - Disclosure - Collaborative Arrangements - Schedule of Daiicho Sankyo (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="CollaborativeArrangementsModernaIncNarrativeDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsModernaIncNarrativeDetails">
        <link:definition>9955532 - Disclosure - Collaborative Arrangements - Moderna, Inc. - 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="CollaborativeArrangementsModernaIncDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsModernaIncDetails">
        <link:definition>9955533 - Disclosure - Collaborative Arrangements - Moderna, Inc. (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="CollaborativeArrangementsBristolMeyersSquibbCompanyNarrativeDetails" roleURI="http://www.merck.com/role/CollaborativeArrangementsBristolMeyersSquibbCompanyNarrativeDetails">
        <link:definition>9955534 - Disclosure - Collaborative Arrangements - Bristol Meyers Squibb Company - 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="RestructuringNarrativeDetails" roleURI="http://www.merck.com/role/RestructuringNarrativeDetails">
        <link:definition>9955535 - Disclosure - Restructuring - 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="RestructuringScheduleofChargesActivitiesbyTypeofCostDetails" roleURI="http://www.merck.com/role/RestructuringScheduleofChargesActivitiesbyTypeofCostDetails">
        <link:definition>9955536 - Disclosure - Restructuring - Schedule of Charges Activities by Type of Cost (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="RestructuringScheduleofChargesActivitiesbyTypeofCostDetails_1" roleURI="http://www.merck.com/role/RestructuringScheduleofChargesActivitiesbyTypeofCostDetails_1">
        <link:definition>9955536 - Disclosure - Restructuring - Schedule of Charges Activities by Type of Cost (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="RestructuringScheduleofActivitiesbyProgramDetails" roleURI="http://www.merck.com/role/RestructuringScheduleofActivitiesbyProgramDetails">
        <link:definition>9955537 - Disclosure - Restructuring - Schedule of Activities by Program (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="FinancialInstrumentsNarrativeDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsNarrativeDetails">
        <link:definition>9955538 - Disclosure - Financial Instruments - 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="FinancialInstrumentsScheduleofEffectofNetInvestmentHedgesDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofEffectofNetInvestmentHedgesDetails">
        <link:definition>9955539 - Disclosure - Financial Instruments - Schedule of Effect of Net Investment Hedges (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="FinancialInstrumentsScheduleofEffectofNetInvestmentHedgesDetails_1" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofEffectofNetInvestmentHedgesDetails_1">
        <link:definition>9955539 - Disclosure - Financial Instruments - Schedule of Effect of Net Investment Hedges (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="FinancialInstrumentsScheduleofInterestRateSwapsHeldDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofInterestRateSwapsHeldDetails">
        <link:definition>9955540 - Disclosure - Financial Instruments - Schedule of Interest Rate Swaps Held (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="FinancialInstrumentsScheduleofAmountsRecordedonBalanceSheetRelatedtoFairValueHedgesDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofAmountsRecordedonBalanceSheetRelatedtoFairValueHedgesDetails">
        <link:definition>9955541 - Disclosure - Financial Instruments - Schedule of Amounts Recorded on Balance Sheet Related to Fair Value Hedges (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="FinancialInstrumentsScheduleofFairValueofDerivativesSegregatedbetweenthoseDerivativesthatareDesignatedasHedgingInstrumentsandthosethatareNotDesignatedasHedgingInstrumentsDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofFairValueofDerivativesSegregatedbetweenthoseDerivativesthatareDesignatedasHedgingInstrumentsandthosethatareNotDesignatedasHedgingInstrumentsDetails">
        <link:definition>9955542 - Disclosure - Financial Instruments - Schedule of Fair Value of Derivatives Segregated between those Derivatives that are Designated as Hedging Instruments and those that are Not Designated as Hedging Instruments (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="FinancialInstrumentsScheduleofFairValueofDerivativesSegregatedbetweenthoseDerivativesthatareDesignatedasHedgingInstrumentsandthosethatareNotDesignatedasHedgingInstrumentsDetails_1" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofFairValueofDerivativesSegregatedbetweenthoseDerivativesthatareDesignatedasHedgingInstrumentsandthosethatareNotDesignatedasHedgingInstrumentsDetails_1">
        <link:definition>9955542 - Disclosure - Financial Instruments - Schedule of Fair Value of Derivatives Segregated between those Derivatives that are Designated as Hedging Instruments and those that are Not Designated as Hedging Instruments (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="FinancialInstrumentsScheduleofInformationonDerivativePositionsSubjecttoMasterNettingArrangementsasiftheywerePresentedonaNetBasisDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofInformationonDerivativePositionsSubjecttoMasterNettingArrangementsasiftheywerePresentedonaNetBasisDetails">
        <link:definition>9955543 - Disclosure - Financial Instruments - Schedule of Information on Derivative Positions Subject to Master Netting Arrangements as if they were Presented on a Net 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="FinancialInstrumentsScheduleofLocationandAmountofPretaxGainsLossesofDerivativesDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofLocationandAmountofPretaxGainsLossesofDerivativesDetails">
        <link:definition>9955544 - Disclosure - Financial Instruments - Schedule of Location and Amount of Pretax (Gains) Losses of Derivatives (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="FinancialInstrumentsScheduleofLocationandAmountofPretaxGainsLossesofDerivativesDetails_1" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofLocationandAmountofPretaxGainsLossesofDerivativesDetails_1">
        <link:definition>9955544 - Disclosure - Financial Instruments - Schedule of Location and Amount of Pretax (Gains) Losses of Derivatives (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="FinancialInstrumentsScheduleofIncomeStatementEffectsonDerivativesNotDesignatedasHedgingInstrumentsDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofIncomeStatementEffectsonDerivativesNotDesignatedasHedgingInstrumentsDetails">
        <link:definition>9955545 - Disclosure - Financial Instruments - Schedule of Income Statement Effects on Derivatives Not Designated as Hedging Instruments (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="FinancialInstrumentsScheduleofIncomeStatementEffectsonDerivativesNotDesignatedasHedgingInstrumentsDetails_1" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofIncomeStatementEffectsonDerivativesNotDesignatedasHedgingInstrumentsDetails_1">
        <link:definition>9955545 - Disclosure - Financial Instruments - Schedule of Income Statement Effects on Derivatives Not Designated as Hedging Instruments (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="FinancialInstrumentsScheduleofInformationonAvailableforsaleInvestmentsDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofInformationonAvailableforsaleInvestmentsDetails">
        <link:definition>9955546 - Disclosure - Financial Instruments - Schedule of Information on Available-for-sale 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="FinancialInstrumentsScheduleofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" roleURI="http://www.merck.com/role/FinancialInstrumentsScheduleofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails">
        <link:definition>9955547 - Disclosure - Financial Instruments - Schedule of Financial Assets and Liabilities Measured at Fair Value on 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="InventoriesScheduleofInventoriesDetails" roleURI="http://www.merck.com/role/InventoriesScheduleofInventoriesDetails">
        <link:definition>9955548 - Disclosure - Inventories - Schedule of Inventories (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="InventoriesScheduleofInventoriesDetails_1" roleURI="http://www.merck.com/role/InventoriesScheduleofInventoriesDetails_1">
        <link:definition>9955548 - Disclosure - Inventories - Schedule of Inventories (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="InventoriesNarrativeDetails" roleURI="http://www.merck.com/role/InventoriesNarrativeDetails">
        <link:definition>9955549 - Disclosure - Inventories - 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="LoansPayableandLongTermDebtDetails" roleURI="http://www.merck.com/role/LoansPayableandLongTermDebtDetails">
        <link:definition>9955550 - Disclosure - Loans Payable and Long-Term Debt (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="ContingenciesDetails" roleURI="http://www.merck.com/role/ContingenciesDetails">
        <link:definition>9955551 - Disclosure - Contingencies (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="EquityDetails" roleURI="http://www.merck.com/role/EquityDetails">
        <link:definition>9955552 - Disclosure - 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="PensionandOtherPostretirementBenefitPlansDetails" roleURI="http://www.merck.com/role/PensionandOtherPostretirementBenefitPlansDetails">
        <link:definition>9955553 - Disclosure - Pension and Other Postretirement Benefit Plans (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="OtherIncomeExpenseNetScheduleofOtherIncomeExpenseNetDetails" roleURI="http://www.merck.com/role/OtherIncomeExpenseNetScheduleofOtherIncomeExpenseNetDetails">
        <link:definition>9955554 - Disclosure - Other (Income) Expense, Net - Schedule of Other (Income) Expense, 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="OtherIncomeExpenseNetNarrativeDetails" roleURI="http://www.merck.com/role/OtherIncomeExpenseNetNarrativeDetails">
        <link:definition>9955555 - Disclosure - Other (Income) Expense, 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="IncomeTaxesDetails" roleURI="http://www.merck.com/role/IncomeTaxesDetails">
        <link:definition>9955556 - Disclosure - 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="LossEarningsPerShareCalculationsofLossEarningsPerShareDetails" roleURI="http://www.merck.com/role/LossEarningsPerShareCalculationsofLossEarningsPerShareDetails">
        <link:definition>9955557 - Disclosure - (Loss) Earnings Per Share - Calculations of (Loss) Earnings Per 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="LossEarningsPerShareNarrativeDetails" roleURI="http://www.merck.com/role/LossEarningsPerShareNarrativeDetails">
        <link:definition>9955558 - Disclosure - (Loss) Earnings Per Share - 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="OtherComprehensiveIncomeLossDetails" roleURI="http://www.merck.com/role/OtherComprehensiveIncomeLossDetails">
        <link:definition>9955559 - Disclosure - Other Comprehensive Income (Loss) (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="SegmentReportingNarrativeDetails" roleURI="http://www.merck.com/role/SegmentReportingNarrativeDetails">
        <link:definition>9955560 - Disclosure - Segment Reporting - 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="SegmentReportingScheduleofSalesfromProductsDetails" roleURI="http://www.merck.com/role/SegmentReportingScheduleofSalesfromProductsDetails">
        <link:definition>9955561 - Disclosure - Segment Reporting - Schedule of Sales from Products (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="SegmentReportingScheduleofConsolidatedSalesbyGeographicAreaDetails" roleURI="http://www.merck.com/role/SegmentReportingScheduleofConsolidatedSalesbyGeographicAreaDetails">
        <link:definition>9955562 - Disclosure - Segment Reporting - Schedule of Consolidated Sales by Geographic 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="SegmentReportingScheduleofReconciliationofSegmentProfitstoIncomebeforeTaxesDetails" roleURI="http://www.merck.com/role/SegmentReportingScheduleofReconciliationofSegmentProfitstoIncomebeforeTaxesDetails">
        <link:definition>9955563 - Disclosure - Segment Reporting - Schedule of Reconciliation of Segment Profits to Income before 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="SegmentReportingScheduleofEquityIncomefromAffiliatesandDepreciationIncludedinSegmentProfitsDetails" roleURI="http://www.merck.com/role/SegmentReportingScheduleofEquityIncomefromAffiliatesandDepreciationIncludedinSegmentProfitsDetails">
        <link:definition>9955564 - Disclosure - Segment Reporting - Schedule of Equity Income from Affiliates and Depreciation Included in Segment Profits (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="SegmentReportingScheduleofPropertyPlantandEquipmentNetbyGeographicAreaDetails" roleURI="http://www.merck.com/role/SegmentReportingScheduleofPropertyPlantandEquipmentNetbyGeographicAreaDetails">
        <link:definition>9955565 - Disclosure - Segment Reporting - Schedule of Property, Plant and Equipment, Net by Geographic Area (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="mrk_A1.875Notesdue2026Member" abstract="true" name="A1.875Notesdue2026Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A3.250NotesDue2032Member" abstract="true" name="A3.250NotesDue2032Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A2.500Notesdue2034Member" abstract="true" name="A2.500Notesdue2034Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A1.375Notesdue2036Member" abstract="true" name="A1.375Notesdue2036Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A3.500NotesDue2037Member" abstract="true" name="A3.500NotesDue2037Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A3.700NotesDue2044Member" abstract="true" name="A3.700NotesDue2044Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A3.750NotesDue2054Member" abstract="true" name="A3.750NotesDue2054Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_CostsExpensesAndOther" abstract="false" name="CostsExpensesAndOther" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AcquisitionsResearchCollaborationsAndLicenseAgreementsTextBlock" abstract="false" name="AcquisitionsResearchCollaborationsAndLicenseAgreementsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="mrk_CollaborativeArrangementsAbstract" abstract="true" name="CollaborativeArrangementsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mrk_OffsettingAssetsAndLiabilitiesTableTextBlock" abstract="false" name="OffsettingAssetsAndLiabilitiesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="mrk_TARGANMember" abstract="true" name="TARGANMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_PelotonTherapeuticsInc.Member" abstract="true" name="PelotonTherapeuticsInc.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_TernsPharmaceuticalsInc.Member" abstract="true" name="TernsPharmaceuticalsInc.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_CidaraTherapeuticsInc.Member" abstract="true" name="CidaraTherapeuticsInc.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_SacTMTMember" abstract="true" name="SacTMTMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_HRS5346JiangsuHengruiPharmaceuticalsCo.Ltd.Member" abstract="true" name="HRS5346JiangsuHengruiPharmaceuticalsCo.Ltd.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_JiangsuHengruiPharmaceuticalsCo.Ltd.Member" abstract="true" name="JiangsuHengruiPharmaceuticalsCo.Ltd.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_WuXiVaccinesFacilityMember" abstract="true" name="WuXiVaccinesFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_WeliregMember" abstract="true" name="WeliregMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_AssetAcquisitionMaximumAggregateSalesBasedMilestonePayments" abstract="false" name="AssetAcquisitionMaximumAggregateSalesBasedMilestonePayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionConsiderationTransferredCashPaymentsToSettleEquityAwards" abstract="false" name="AssetAcquisitionConsiderationTransferredCashPaymentsToSettleEquityAwards" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionConsiderationTransferredSettlementOfUnvestedShareBasedPaymentAwards" abstract="false" name="AssetAcquisitionConsiderationTransferredSettlementOfUnvestedShareBasedPaymentAwards" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionAssetsAcquiredAndLiabilitiesAssumedNet" abstract="false" name="AssetAcquisitionAssetsAcquiredAndLiabilitiesAssumedNet" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionCashAndCashEquivalents" abstract="false" name="AssetAcquisitionCashAndCashEquivalents" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionInvestments" abstract="false" name="AssetAcquisitionInvestments" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionDeferredTaxAssets" abstract="false" name="AssetAcquisitionDeferredTaxAssets" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionNetLiabilitiesOther" abstract="false" name="AssetAcquisitionNetLiabilitiesOther" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionMaximumAggregateRegulatoryMilestonePayments" abstract="false" name="AssetAcquisitionMaximumAggregateRegulatoryMilestonePayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_OtherNontradeReceivable" abstract="false" name="OtherNontradeReceivable" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AssetAcquisitionMaximumAggregateContingentDevelopmentRelatedPayments" abstract="false" name="AssetAcquisitionMaximumAggregateContingentDevelopmentRelatedPayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AstraZenecaMember" abstract="true" name="AstraZenecaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_AllianceRevenueKoselugoMember" abstract="true" name="AllianceRevenueKoselugoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_LynparzaMember" abstract="true" name="LynparzaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_KoselugoMember" abstract="true" name="KoselugoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_LicensesAndOtherMember" abstract="true" name="LicensesAndOtherMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_CollaborativeArrangementUpfrontPaymentsReceivedRecognizedAsRevenue" abstract="false" name="CollaborativeArrangementUpfrontPaymentsReceivedRecognizedAsRevenue" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementFutureFixedUpfrontPaymentsFromCollaborativePartner" abstract="false" name="CollaborativeArrangementFutureFixedUpfrontPaymentsFromCollaborativePartner" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsMaximumAggregateRegulatoryMilestonePayments" abstract="false" name="CollaborativeArrangementRightsAndObligationsMaximumAggregateRegulatoryMilestonePayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementMilestonePaymentFromCollaborativePartner" abstract="false" name="CollaborativeArrangementMilestonePaymentFromCollaborativePartner" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRoyaltiesOnNetSalesPercent" abstract="false" name="CollaborativeArrangementRoyaltiesOnNetSalesPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsMaximumAggregateSalesBasedMilestonePayments" abstract="false" name="CollaborativeArrangementRightsAndObligationsMaximumAggregateSalesBasedMilestonePayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsMilestonePaymentsSalesBased" abstract="false" name="CollaborativeArrangementRightsAndObligationsMilestonePaymentsSalesBased" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AlliancerevenueLynparzaMember" abstract="true" name="AlliancerevenueLynparzaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_EisaiMember" abstract="true" name="EisaiMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_LenvimaMember" abstract="true" name="LenvimaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_BayerAGMember" abstract="true" name="BayerAGMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_AdempasMember" abstract="true" name="AdempasMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_VerquvoMember" abstract="true" name="VerquvoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_RidgebackBiotherapeuticsLPMember" abstract="true" name="RidgebackBiotherapeuticsLPMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_LagevrioMember" abstract="true" name="LagevrioMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_ResearchAndDevelopmentExpenseReimbursement" abstract="false" name="ResearchAndDevelopmentExpenseReimbursement" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_DaiichiSankyoMember" abstract="true" name="DaiichiSankyoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_IfinatamabDeruxtecanMember" abstract="true" name="IfinatamabDeruxtecanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_PatritumabDeruxtecanMember" abstract="true" name="PatritumabDeruxtecanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_RaludotatugDeruxtecanMember" abstract="true" name="RaludotatugDeruxtecanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsNumberOfAntibodyDrugConjugates" abstract="false" name="CollaborativeArrangementRightsAndObligationsNumberOfAntibodyDrugConjugates" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsAggregateUpfrontPaymentsDueUponExecution" abstract="false" name="CollaborativeArrangementRightsAndObligationsAggregateUpfrontPaymentsDueUponExecution" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsRefundableUpfrontPayments" abstract="false" name="CollaborativeArrangementRightsAndObligationsRefundableUpfrontPayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsAggregateUpfrontPaymentsDueUponLapseOfTime" abstract="false" name="CollaborativeArrangementRightsAndObligationsAggregateUpfrontPaymentsDueUponLapseOfTime" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsMaximumAggregateContingentMilestonePaymentsPerProduct" abstract="false" name="CollaborativeArrangementRightsAndObligationsMaximumAggregateContingentMilestonePaymentsPerProduct" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsLiableContractedPortionAmountOfResearchAndDevelopmentExpensesToIncurCostsForPercentage" abstract="false" name="CollaborativeArrangementRightsAndObligationsLiableContractedPortionAmountOfResearchAndDevelopmentExpensesToIncurCostsForPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsLiableContractedPortionAmountOfResearchAndDevelopmentExpensesToIncurCostsFor" abstract="false" name="CollaborativeArrangementRightsAndObligationsLiableContractedPortionAmountOfResearchAndDevelopmentExpensesToIncurCostsFor" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_CollaborativeArrangementRightsAndObligationsRoyaltyPercentageOnSales" abstract="false" name="CollaborativeArrangementRightsAndObligationsRoyaltyPercentageOnSales" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mrk_ProceedsFromUpfrontPaymentCash" abstract="false" name="ProceedsFromUpfrontPaymentCash" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_ModernaInc.Member" abstract="true" name="ModernaInc.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_BristolMyersSquibbCompanyMember" abstract="true" name="BristolMyersSquibbCompanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_AllianceRevenueReblozylMember" abstract="true" name="AllianceRevenueReblozylMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_RoyaltyRatePercentage" abstract="false" name="RoyaltyRatePercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mrk_RoyaltyRateDeductionPercentage" abstract="false" name="RoyaltyRateDeductionPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mrk_RestructuringProgram2025Member" abstract="true" name="RestructuringProgram2025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_RestructuringProgram2024Member" abstract="true" name="RestructuringProgram2024Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_RestructuringAndRelatedCostExpectedPretaxCostsCashPercentage" abstract="false" name="RestructuringAndRelatedCostExpectedPretaxCostsCashPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mrk_RestructuringAndRelatedCostExpectedPretaxCostsNonCashPercentage" abstract="false" name="RestructuringAndRelatedCostExpectedPretaxCostsNonCashPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mrk_AcceleratedDepreciationMember" abstract="true" name="AcceleratedDepreciationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_RestructuringReserveIncreaseDecreaseNoncashActivity" abstract="false" name="RestructuringReserveIncreaseDecreaseNoncashActivity" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_AccountsReceivableFactoringCollectionsMember" abstract="true" name="AccountsReceivableFactoringCollectionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A450NoteDue2033Member" abstract="true" name="A450NoteDue2033Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A5.20NotesDue2036Member" abstract="true" name="A5.20NotesDue2036Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_EurodominatedNotesMember" abstract="true" name="EurodominatedNotesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A4.75NotesDue2035Member" abstract="true" name="A4.75NotesDue2035Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A5.00NoteDue2053Member" abstract="true" name="A5.00NoteDue2053Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_ForeignGovernmentBondsMember" abstract="true" name="ForeignGovernmentBondsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_DebtSecuritiesandEquitySecuritiesFVNI" abstract="false" name="DebtSecuritiesandEquitySecuritiesFVNI" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_July2026ExpirationMember" abstract="true" name="July2026ExpirationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_August2026ExpirationMember" abstract="true" name="August2026ExpirationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_InventoryWorkInProcessAndRawMaterialsExcludingSupplies" abstract="false" name="InventoryWorkInProcessAndRawMaterialsExcludingSupplies" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_InventoryNetAndInventoryNoncurrent" abstract="false" name="InventoryNetAndInventoryNoncurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_RecognizedAsAbstract" abstract="true" name="RecognizedAsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mrk_InventoryTable" abstract="true" name="InventoryTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="mrk_InventoryNotExpectedtobeSoldWithinOneYearMember" abstract="true" name="InventoryNotExpectedtobeSoldWithinOneYearMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_InventoriesProducedinPreparationforProductLaunchesMember" abstract="true" name="InventoriesProducedinPreparationforProductLaunchesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_FloatingRateNotesDue2028Member" abstract="true" name="FloatingRateNotesDue2028Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A4.30NotesDue2028Member" abstract="true" name="A4.30NotesDue2028Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A4.65NotesDue2031Member" abstract="true" name="A4.65NotesDue2031Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A4.95NotesDue2033Member" abstract="true" name="A4.95NotesDue2033Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A5.75NotesDue2046Member" abstract="true" name="A5.75NotesDue2046Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_A5.85NotesDue2056Member" abstract="true" name="A5.85NotesDue2056Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_Dr.SchollsMember" abstract="true" name="Dr.SchollsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_GardasilGardasil9Member" abstract="true" name="GardasilGardasil9Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_BridionMember" abstract="true" name="BridionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_KeytrudaMember" abstract="true" name="KeytrudaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_SubcutaneousPembrolizumabMember" abstract="true" name="SubcutaneousPembrolizumabMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_MotionForSummaryJudgementGrantedMember" abstract="true" name="MotionForSummaryJudgementGrantedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_PGRPetitionMember" abstract="true" name="PGRPetitionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_PGRPetitionProcessIneligibleToBeChallengedMember" abstract="true" name="PGRPetitionProcessIneligibleToBeChallengedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_LegalDefenseCostsMember" abstract="true" name="LegalDefenseCostsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_LossContingencyPatentsUnpatentableNumber" abstract="false" name="LossContingencyPatentsUnpatentableNumber" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mrk_LossContingencyAdditionalUnpatentablePatentsNumber" abstract="false" name="LossContingencyAdditionalUnpatentablePatentsNumber" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mrk_LossContingencyRegulatoryStayDuration" abstract="false" name="LossContingencyRegulatoryStayDuration" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mrk_StockholdersEquityTable" abstract="true" name="StockholdersEquityTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="mrk_StockholdersEquityLineItems" abstract="true" name="StockholdersEquityLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mrk_OtherNonoperatingIncomeExpenseOther" abstract="false" name="OtherNonoperatingIncomeExpenseOther" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_IncomeTaxEstimationEstimationExpenseTypeAxis" abstract="true" name="IncomeTaxEstimationEstimationExpenseTypeAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="mrk_IncomeTaxEstimationEstimationExpenseTypeDomain" abstract="true" name="IncomeTaxEstimationEstimationExpenseTypeDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_PenaltiesMember" abstract="true" name="PenaltiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_SalesDiscounts" abstract="false" name="SalesDiscounts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_KeytrudaQlexMember" abstract="true" name="KeytrudaQlexMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_ProQuadMMRIIVarivaxMember" abstract="true" name="ProQuadMMRIIVarivaxMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_VaxneuvanceMember" abstract="true" name="VaxneuvanceMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_RotateqMember" abstract="true" name="RotateqMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_CapvaxiveMember" abstract="true" name="CapvaxiveMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_WinrevairMember" abstract="true" name="WinrevairMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_OhtuvayreMember" abstract="true" name="OhtuvayreMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_AllianceRevenueAdempasVerquvoMember" abstract="true" name="AllianceRevenueAdempasVerquvoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_PrevymisMember" abstract="true" name="PrevymisMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_DelstrigoMember" abstract="true" name="DelstrigoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_ZerbaxaMember" abstract="true" name="ZerbaxaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_IsentressIsentressHDMember" abstract="true" name="IsentressIsentressHDMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_DificidMember" abstract="true" name="DificidMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_JanuviaMember" abstract="true" name="JanuviaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_JanumetMember" abstract="true" name="JanumetMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_OtherPharmaceuticalMember" abstract="true" name="OtherPharmaceuticalMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_LivestockMember" abstract="true" name="LivestockMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_CompanionAnimalMember" abstract="true" name="CompanionAnimalMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_PharmaceuticalsegmentMember" abstract="true" name="PharmaceuticalsegmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_AnimalHealthsegmentMember" abstract="true" name="AnimalHealthsegmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_IncreaseDecreaseInHedgeRevenue" abstract="false" name="IncreaseDecreaseInHedgeRevenue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mrk_OtherCountriesMember" abstract="true" name="OtherCountriesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mrk_SegmentReportingUnallocatedOtherExpensesNet" abstract="false" name="SegmentReportingUnallocatedOtherExpensesNet" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
