Biogen Shares Fall 6% After Positive Trial

Biogen's stock fell 6% by Thursday close despite reporting positive Phase 2 results for diranersen in Alzheimer’s disease.
The Phase 2 CELIA study of 416 participants showed tau reductions and slowed decline, especially at 60 mg every 24 weeks.
The trial missed its primary endpoint of dose‑response on Clinical Dementia Rating‑Sum of Boxes at Week 76, prompting caution.
Biogen plans to advance diranersen to registrational development; FDA granted Fast Track in 2025 and data will be presented at AAIC 2026.