Biogen falls as experimental Alzheimer's drug misses main trial goal

Shares of drugmaker Biogen BIIB.O fell 3.9% to $196.45 after the company said its experimental Alzheimer's drug diranersen missed the main goal of its mid-stage study, which tested whether higher doses provided greater benefit in patients with early Alzheimer's disease.

The company said the drug, however, slowed decline in memory, thinking and daily functioning in the trial.

A 60 mg dose slowed decline by 42% and 50% on two key memory and thinking tests, with most results statistically significant.

All doses reduced levels of tau, a protein linked to Alzheimer's disease, the company said.

Biogen plans a late-stage confirmatory trial. The FDA granted fast track status to diranersen in 2025.

As of the last close, the stock was up about 19% year to date.