Ionis Pharmaceuticals, Inc. (IONS) Faces Investor Scrutiny After Surprise Trial Failure Drives Stock Down 23% – HBSS

Investors in Ionis Pharmaceuticals, Inc. (NASDAQ: IONS) saw the price of their shares plunge $20.19 (-23%) on July 9, 2026 after the commercial stage biotech company and its partner (AstraZeneca) announced that a late-stage trial for an experimental heart disease therapy did not meet its target.

The surprise result and severe market reaction have prompted national shareholders’ rights firm Hagens Berman to open an investigation into whether Ionis was sufficiently transparent about the trial’s data and design and, if not, whether the company may have violated the federal securities laws.

The investigation is focused on Ionis’ statements regarding the development of eplontersen, a medicine intended to treat patients with transthyretin amyloidosis cardiomyopathy, or ATTR-CM. The company completed enrollment in the Phase 3 CARDIO-TTRansform study in July 2023.

Just last month, Ionis touted the Phase 3 study as “the largest study ever conducted by far” in ATTR-CM, setting the company up “for the richest dataset for not only the primary endpoint, but the secondary endpoints.” Ionis also assured investors that “everything is going very well in the conduct of the study and execution.”

Investors’ expectations were dashed on July 9, 2026 when Ionis announced that the Phase 3 CARDIO-TTRansform trial did not meet the primary efficacy endpoint – “[i]n this contemporary patient population treated with standard of care, including a majority on a stabilizer, adding eplontersen did not provide a statistically significant benefit.”

The company further revealed that “57% of patients in each arm received a stabilizer treatment at baseline, and a further 24% in each arm initiated a stabilizer during the trial.” In response, the market swiftly reacted by wiping out over $3.3 billion of Ionis’ market capitalization.

In addition, one prominent analyst reportedly wrote “Unbeknownst to us, > 80% of CARDIO-TTRansform participants were on stabilizer […] driving the failure of the primary endpoint[.]”

“Our investigation is focused on when Ionis and its management first knew about the apparent problems with the trial data or its design and whether they were sufficiently transparent to investors,” said Reed Kathrein, the Hagens Berman partner leading the firm’s investigation.