<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2014-06-11</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001428522</issuerCik>
        <issuerName>Radius Health, Inc.</issuerName>
        <issuerTradingSymbol>RDUS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001610441</rptOwnerCik>
            <rptOwnerName>F2 Bioscience VI L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>PO BOX 309, UGLAND HOUSE</rptOwnerStreet1>
            <rptOwnerStreet2>SOUTH CHURCH STREET</rptOwnerStreet2>
            <rptOwnerCity>GEORGE TOWN</rptOwnerCity>
            <rptOwnerState>E9</rptOwnerState>
            <rptOwnerZipCode>KY1-1104</rptOwnerZipCode>
            <rptOwnerStateDescription>CAYMAN ISLANDS</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001575753</rptOwnerCik>
            <rptOwnerName>F2 Capital Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3RD FLOOR, GENEVE PLACE, WATERFRONT DR</rptOwnerStreet1>
            <rptOwnerStreet2>PO BOX 3175, ROAD TOWN</rptOwnerStreet2>
            <rptOwnerCity>TORTOLA</rptOwnerCity>
            <rptOwnerState>D8</rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription>VIRGIN ISLANDS, BRITISH</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001575748</rptOwnerCik>
            <rptOwnerName>Priestley Katherine</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>SUITE 6, ALBION RIVERSIDE BUILDING</rptOwnerStreet1>
            <rptOwnerStreet2>8 HESTER ROAD</rptOwnerStreet2>
            <rptOwnerCity>LONDON</rptOwnerCity>
            <rptOwnerState>X0</rptOwnerState>
            <rptOwnerZipCode>SW11 4AX</rptOwnerZipCode>
            <rptOwnerStateDescription>UNITED KINGDOM</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001600769</rptOwnerCik>
            <rptOwnerName>Globeways Holdings Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3RD FLOOR, GENEVE PLACE, WATERFRONT DR</rptOwnerStreet1>
            <rptOwnerStreet2>PO BOX 3175, ROAD TOWN</rptOwnerStreet2>
            <rptOwnerCity>TORTOLA</rptOwnerCity>
            <rptOwnerState>D8</rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription>VIRGIN ISLANDS, BRITISH</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001600632</rptOwnerCik>
            <rptOwnerName>F2 Bioscience IV GP Ltd.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>PO BOX 309, UGLAND HOUSE</rptOwnerStreet1>
            <rptOwnerStreet2>SOUTH CHURCH STREET</rptOwnerStreet2>
            <rptOwnerCity>GEORGE TOWN</rptOwnerCity>
            <rptOwnerState>E9</rptOwnerState>
            <rptOwnerZipCode>KY1-1104</rptOwnerZipCode>
            <rptOwnerStateDescription>CAYMAN ISLANDS</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>587500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The reported securities are owned directly by F2 Bioscience VI L.P. (&quot;F2 Science&quot;). F2 Bioscience IV GP Ltd. (&quot;F2 IV GP&quot;) is the General Partner of F2 Science.  Katherine Priestley and Globeways Holdings Limited are members of F2 IV GP.  F2 Capital Limited is an investment adviser to F2 Science. Each of the reporting persons disclaims beneficial ownership of the securities reported herein except to the extent of their pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of all of the reported shares for purposes of Section 16 or for any other purpose.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Morag Law, attorney-in-fact for F2 Bioscience VI, L.P.</signatureName>
        <signatureDate>2014-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Morag Law, attorney-in-fact for F2 Bioscience IV GP Ltd.</signatureName>
        <signatureDate>2014-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Morag Law, attorney-in-fact for F2 Capital Ltd.</signatureName>
        <signatureDate>2014-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Morag Law, attorney-in-fact for Katherine Priestley</signatureName>
        <signatureDate>2014-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Morag Law, attorney-in-fact for Globeways Holdings Ltd.</signatureName>
        <signatureDate>2014-06-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
