<SEC-DOCUMENT>0001897612-25-000512.txt : 20251114
<SEC-HEADER>0001897612-25-000512.hdr.sgml : 20251114
<ACCEPTANCE-DATETIME>20251114121824
ACCESSION NUMBER:		0001897612-25-000512
CONFORMED SUBMISSION TYPE:	SCHEDULE 13G/A
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20251114
DATE AS OF CHANGE:		20251114

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			IONIS PHARMACEUTICALS INC
		CENTRAL INDEX KEY:			0000874015
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		EIN:				330336973
		STATE OF INCORPORATION:			CA
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-41771
		FILM NUMBER:		251483374

	BUSINESS ADDRESS:	
		STREET 1:		2855 GAZELLE COURT
		CITY:			CARLSBAD
		STATE:			CA
		ZIP:			92010
		BUSINESS PHONE:		7609319200

	MAIL ADDRESS:	
		STREET 1:		2855 GAZELLE COURT
		CITY:			CARLSBAD
		STATE:			CA
		ZIP:			92010

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ISIS PHARMACEUTICALS INC
		DATE OF NAME CHANGE:	19930328

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			T. Rowe Price Investment Management, Inc.
		CENTRAL INDEX KEY:			0001897612
		ORGANIZATION NAME:           	
		EIN:				854328500
		STATE OF INCORPORATION:			MD
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G/A

	BUSINESS ADDRESS:	
		STREET 1:		1307 POINT STREET
		CITY:			BALTIMORE
		STATE:			MD
		ZIP:			21231
		BUSINESS PHONE:		000-000-0000

	MAIL ADDRESS:	
		STREET 1:		1307 POINT STREET
		CITY:			BALTIMORE
		STATE:			MD
		ZIP:			21231
</SEC-HEADER>
<DOCUMENT>
<TYPE>SCHEDULE 13G/A
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
<XML>
<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/schedule13g" xmlns:ns2="http://www.sec.gov/edgar/common">
    <headerData>
        <submissionType>SCHEDULE 13G/A</submissionType>
        <previousAccessionNumber>0001897612-24-001128</previousAccessionNumber>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001897612</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>


        </filerInfo>
    </headerData>
    <formData>
        <coverPageHeader>
            <amendmentNo>3</amendmentNo>
            <securitiesClassTitle>COMMON STOCK</securitiesClassTitle>
            <eventDateRequiresFilingThisStatement>09/30/2025</eventDateRequiresFilingThisStatement>
            <issuerInfo>
                <issuerCik>0000874015</issuerCik>
                <issuerName>IONIS PHARMACEUTICALS INC</issuerName>
                <issuerCusip>462222100</issuerCusip>
                <issuerPrincipalExecutiveOfficeAddress>
                    <ns2:street1>2855 GAZELLE COURT</ns2:street1>
                    <ns2:city>CARLSBAD</ns2:city>
                    <ns2:stateOrCountry>CA</ns2:stateOrCountry>
                    <ns2:zipCode>92010</ns2:zipCode>
                </issuerPrincipalExecutiveOfficeAddress>
            </issuerInfo>
            <designateRulesPursuantThisScheduleFiled>
                <designateRulePursuantThisScheduleFiled>Rule 13d-1(b)</designateRulePursuantThisScheduleFiled>
            </designateRulesPursuantThisScheduleFiled>
        </coverPageHeader>
        <coverPageHeaderReportingPersonDetails>

            <reportingPersonName>T. Rowe Price Investment Management, Inc.</reportingPersonName>
            <citizenshipOrOrganization>MD</citizenshipOrOrganization>
            <reportingPersonBeneficiallyOwnedNumberOfShares>
                <soleVotingPower>13044284</soleVotingPower>
                <sharedVotingPower>0</sharedVotingPower>
                <soleDispositivePower>13157114</soleDispositivePower>
                <sharedDispositivePower>0</sharedDispositivePower>
            </reportingPersonBeneficiallyOwnedNumberOfShares>
            <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>13157114</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
            <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
            <classPercent>8.3</classPercent>
            <typeOfReportingPerson>IA</typeOfReportingPerson>
        </coverPageHeaderReportingPersonDetails>
        <items>
            <item1>
                <issuerName>IONIS PHARMACEUTICALS INC</issuerName>
                <issuerPrincipalExecutiveOfficeAddress>2855 GAZELLE COURT, CARLSBAD, CA, 92010</issuerPrincipalExecutiveOfficeAddress>
            </item1>
            <item2>
                <filingPersonName>T. Rowe Price Investment Management, Inc.</filingPersonName>
                <principalBusinessOfficeOrResidenceAddress>1307 Point Street, Baltimore, MD 21231</principalBusinessOfficeOrResidenceAddress>
                <citizenship>Maryland</citizenship>
            </item2>
            <item3>
                <notApplicableFlag>N</notApplicableFlag>
                <typeOfPersonFiling>IA</typeOfPersonFiling>
            </item3>
            <item4>
                <amountBeneficiallyOwned>13157114</amountBeneficiallyOwned>
                <classPercent>8.3</classPercent>
                <numberOfSharesPersonHas>
                    <solePowerOrDirectToVote>13044284</solePowerOrDirectToVote>
                    <sharedPowerOrDirectToVote>0</sharedPowerOrDirectToVote>
                    <solePowerOrDirectToDispose>13157114</solePowerOrDirectToDispose>
                    <sharedPowerOrDirectToDispose>0</sharedPowerOrDirectToDispose>
                </numberOfSharesPersonHas>
            </item4>
            <item5>
                <notApplicableFlag>Y</notApplicableFlag>
            </item5>
            <item6>
                <notApplicableFlag>Y</notApplicableFlag>
            </item6>
            <item7>
                <notApplicableFlag>Y</notApplicableFlag>
            </item7>
            <item8>
                <notApplicableFlag>Y</notApplicableFlag>
            </item8>
            <item9>
                <notApplicableFlag>Y</notApplicableFlag>
            </item9>
            <item10>
                <notApplicableFlag>N</notApplicableFlag>
                <certifications>By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. T. Rowe Price Investment Management, Inc. hereby declares and affirms that the filing of Schedule 13G shall not be construed as an admission that Price Investment Management is the beneficial owner of the securities referred to, which beneficial ownership is expressly denied.</certifications>
            </item10>
        </items>
        <signatureInformation>
            <reportingPersonName>T. Rowe Price Investment Management, Inc.</reportingPersonName>
            <signatureDetails>
                <signature>Ellen York</signature>
                <title>Vice President</title>
                <date>11/14/2025</date>
            </signatureDetails>
        </signatureInformation>
    </formData>
</edgarSubmission>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
