Biogen Stock Slides After Trial Miss, But Analysts Stay Bullish

Summary

Biogen Today$189.47 +1.67 (+0.89%) As of 05/21/2026 04:00 PM Eastern52-Week Range$121.05▼$205.97P/E Ratio20.33Price Target$215.62 U.S. Food & Drug Administration (FDA) events crystallize the risk/reward thesis for many biotechnology stocks, and Biogen Inc.'s NASDAQ: BIIB latest Alzheimer’s update shows why that trade can turn quickly. Biogen entered May with momentum after a solid first-quarter earnings report and its planned acquisition of Apellis Pharmaceuticals NASDAQ: APLS for $41 per share, which would add two commercialized rare disease and immunology drugs and a nephrology infrastructure to anchor the felzartamab launch.Get Biogen alerts:Sign Up The bigger driver, however, was anticipation for Phase 2 data from CELIA, a study of diranersen, Biogen’s experimental tau-targeting treatment for Alzheimer’s disease. That readout arrived on May 14 and produced a mixed reaction. Diranersen missed its primary endpoint, which measured dose response on the Clinical Dementia Rating-Sum of Boxes at Week 76, and BIIB fell more than 10%. But the selloff may not tell the full story: Biogen still reported meaningful reductions in tau pathology and signs of slower clinical decline, giving investors a reason to keep the drug—and the stock’s long-term Alzheimer’s thesis—in focus. Why Tau Matters for Biogen’s Alzheimer’s PipelineDiranersen is an antisense oligonucleotide (ASO) therapy that targets tau. Tau is a protein that stabilizes the internal transport system neurons use to carry nutrients and signals. In Alzheimer’s disease, tau can become chemically altered, detach from its structural role and form tangles inside brain cells. Along with amyloid plaques, those tangles are a defining feature of the disease, disrupting cellular communication, contributing to neuron death and tracking closely with the cognitive decline patients experience. For investors, tau matters because it appears to be the more proximate driver of symptoms. A drug that reduces tau pathology, such as diran...