Ionis Pharmaceuticals Drops Another 9% as Bad News Piles Up

By Danielle Liverance Published Jul 10, 3:37PM EDT

Quick Read

IONS fell 21% this week after the Phase 3 eplontersen ATTR-CM trial missed its primary endpoint, with a monotherapy subgroup hinting at partial efficacy.
ALNY slipped 3.6% despite analysts flagging its Amvuttra as a direct beneficiary of eplontersen's miss, while BIIB bucked the selloff, rising 0.5%.
Three catalysts loom: full ESC trial data in August, a PDUFA for Alexander disease in September, and a hepatitis B decision in October.
Act now: the analyst who called NVIDIA in 2010 just named his top 10 AI stocks — and Ionis Pharmaceuticals didn't make the cut. Grab the names FREE today.

Ionis Pharmaceuticals Drops Another 9% as Bad News Piles Up — © gorodenkoff / iStock via Getty Images

Shares of Ionis Pharmaceuticals (NASDAQ:IONS | IONS Price Prediction) are down 9% intraday, changing hands near $58.30 after opening the session at $64.27. The slide caps a brutal stretch for the RNA-targeted drug developer, with the stock now off over 25% over the past week.

Phase 3 Heart Trial Failure Drives the Selloff

The catalyst is a clinical setback. On July 9, 2026, Ionis and partner AstraZeneca disclosed that the Phase 3 CARDIO-TTRansform study of eplontersen in transthyretin-mediated amyloid cardiomyopathy (ATTR-CM) failed to meet its primary efficacy endpoint in the overall patient population. That is the same program flagged as a key value driver heading into the back half of 2026, and the reaction has been swift.

Peers Mostly Lower, but Rivals in ATTR-CM Stand to Benefit

The reaction across RNA and rare-disease biotech is uneven. Alnylam Pharmaceuticals (NASDAQ:ALNY), whose Amvuttra competes directly in ATTR-CM, is down 3.6% to $302. That is a notable move given that Benzinga flagged Amvuttra as one of the rivals standing to gain from the eplontersen miss, alongside BridgeBio’s Attruby. The initial read from the Street is that existing second-generation monotherapies now face less near-term competitive pressure.

Arrowhead Pharmaceuticals (NASDAQ:ARWR), another RNAi developer, is down 8.3% to $77, tracking the sector sympathy move despite the mostly unrelated business. Sarepta Therapeutics (NASDAQ:SRPT) is off 6.5% to $19. Ionis collaborator Biogen (NASDAQ:BIIB), which co-develops multiple antisense assets with Ionis, is bucking the group and trading up 0.5% to $200.

Ionis was priced for a lot going into this readout. The stock had roughly doubled over the past year until July 7th.

What to Watch Next

Two catalysts sit directly in front of investors. The full CARDIO-TTRansform dataset lands at ESC in August, which will help point to any subgroup opportunities. The zilganersen PDUFA for Alexander disease is set for September 22, 2026, followed by the bepirovirsen decision in chronic hepatitis B on October 26. Keep an eye on whether Ionis holds above the $40 52-week low as the dust settles.

Contact [email protected] for any questions or corrections.

Follow 24/7 Wall St. on Google

About the Author Danielle Liverance →

I've spent more than 15 years inside enterprise software, working alongside the finance, sales operations, and HR leaders who run the revenue engines at some of the largest tech companies in the country.

My day job is helping enterprise executives make smarter decisions about retention, compensation, and growth. These are the same operational levers that show up in every earnings report investors actually read. That perspective shapes my writing for 24/7 Wall St.

The headline numbers are easy. The interesting stuff is underneath: how companies make money, what executives are worried about, and what any of it means for the person checking their 401(k) on a Sunday afternoon. I write about personal finance and business as someone who has spent her career inside the rooms where these decisions get made.