Aducanumab's contested approval (2021)
The FDA approved Biogen's amyloid drug aducanumab, sold as Aduhelm, based on its ability to clear amyloid, even though two trials gave conflicting results on whether it helped patients. An advisory panel had voted against it, and several members resigned.
Insurers and doctors largely refused to use it, and sales collapsed.
Biogen pulled the drug in 2024, and the episode made regulators and analysts wary of biomarker-only approvals.
Diranersen also missed its main clinical goal while moving a biomarker. That history shapes how regulators and investors will read Biogen's push to advance it.
