SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of report (Date of earliest event reported): June 24, 2026

IONIS PHARMACEUTICALS, INC.

(Exact Name of Registrant as Specified in Charter)

Delaware

(State or Other Jurisdiction of Incorporation)

2855 Gazelle Court

Carlsbad, CA 92010

(Address of Principal Executive Offices and Zip Code)

Registrant’s telephone number, including area code: (760) 931-9200

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Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (Section 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (Section 240.12b-2 of this chapter).

Emerging growth company   ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.          ☐

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Item 7.01          Regulation FD Disclosure.

On June 24, 2026, Ionis Pharmaceuticals, Inc. (“Ionis”) issued a press release announcing that the U.S. Food and Drug Administration (“FDA”) has approved TRYNGOLZA® (olezarsen) as an adjunct to diet to reduce triglycerides (“TG”) and the risk of acute pancreatitis in adults with severe hypertriglyceridemia (“sHTG”: TG greater than or equal to 500 mg/dL). A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

The information in this Item 7.01 and the exhibit attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, regardless of any general incorporation language in such filing.

Item 8.01          Other Events.

On June 24, 2026, Ionis announced that the U.S. FDA has approved TRYNGOLZA® (olezarsen) as an adjunct to diet to reduce triglycerides and the risk of acute pancreatitis in adults with sHTG. TRYNGOLZA is available in a 50 mg or 80 mg dose and is self-administered once monthly via an autoinjector. sHTG is characterized by an increased risk of acute pancreatitis, which causes debilitating abdominal pain that often leads to repeated and prolonged hospitalization, permanent organ damage and can be life-threatening.

The FDA approval was based on positive results from the Phase 3 CORE and CORE2 studies, which were published in The New England Journal of Medicine.

In the CORE and CORE2 studies, TRYNGOLZA demonstrated rapid and consistent triglyceride control, lowering fasting triglyceride levels by up to 72% compared to placebo at six months and sustaining those reductions at 12 months. Additionally, TRYNGOLZA significantly reduced acute pancreatitis events by up to 91%. Among patients treated with TRYNGOLZA with baseline and 12-month data, 86% achieved triglyceride levels below 500 mg/dL, a critical threshold for reducing acute pancreatitis risk. The number needed to treat (“NNT”) over one year to prevent one episode of acute pancreatitis was 20 in the overall cohort and four in patients with triglycerides ≥880 mg/dL and a prior history of acute pancreatitis, indicating a strong clinical benefit across the spectrum of sHTG patients and an exceptional clinical benefit in the highest risk subgroup.

Across the clinical program, TRYNGOLZA demonstrated a favorable safety and tolerability profile. The most common adverse reactions in patients with sHTG (incidence ≥2% higher than placebo) were injection site reactions and liver enzyme increases.

TRYNGOLZA will be available for sHTG in the U.S. in July.

Forward-Looking Statements

This report includes forward-looking statements regarding Ionis’ business and the therapeutic and commercial potential of TRYNGOLZA, Ionis’ technologies and other products in development. Any statement describing Ionis’ goals, expectations, financial or other projections, intentions or beliefs is a forward-looking statement and should be considered an at-risk statement. Such statements are subject to certain risks and uncertainties including those inherent in the process of discovering, developing and commercializing medicines that are safe and effective for use as human therapeutics, and in the endeavor of building a business around such medicines. Ionis’ forward-looking statements also involve assumptions that, if they never materialize or prove correct, could cause its results to differ materially from those expressed or implied by such forward-looking statements. Although Ionis’ forward-looking statements reflect the good faith judgment of its management, these statements are based only on facts and factors currently known by Ionis. Except as required by law, Ionis undertakes no obligation to update any forward-looking statements for any reason. As a result, you are cautioned not to rely on these forward-looking statements. These and other risks concerning Ionis’ programs are described in additional detail in Ionis’ annual report on Form 10-K for the year ended December 31, 2025, and most recent Form 10-Q, which are on file with the Securities and Exchange Commission. Copies of these and other documents are available from the Company.

Item 9.01          Financial Statements and Exhibits.

(d) Exhibits.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

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