Biogen stock was down more than 7% Tuesday morning--on pace for its largest drop since 2020--after the company's tau-targeting drug failed to perform any better than the Alzheimer's drugs already on the market. On a standard dementia scale, patients taking Biogen's experimental drug diranersen saw a 26% slowing in the rate of cognitive decline, roughly in line with the company's drug Leqembi.

Diranersen, which failed to meet its primary goal in a clinical trial in May, did succeed in cutting a protein called tau in patients' spinal fluid by as much as 65%, according to data presented Tuesday at the Alzheimer's Association International Conference. The company says it plans to move the drug into late-stage testing.

--Tau is the target of a growing wave of Alzheimer's research, as drugmakers look for more potent ways to slow the disease after the first few approved drugs showed just modest benefit.

--Tuesday's drop comes a day after Biogen shares jumped 5% Monday, after the Food and Drug Administration approved an at-home, self-administered starter dose of Leqembi. Previously, that initial treatment was only available through infusions given at a clinic.

Write to Xavier Martinez at xavier.martinez@wsj.com

(END) Dow Jones Newswires

July 14, 2026 11:56 ET (15:56 GMT)

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