Why did BIIB's Q1 2024 earnings miss forecasts?

Biogen's Q1 2024 earnings missed forecasts due to a combination of factors:

1. **Decline in Multiple Sclerosis Drug Sales**: Biogen's multiple sclerosis therapies, which include Tecfidera and Tysabri, experienced a significant drop in sales. These drugs are crucial to the company's revenue, and their decline contributed to the overall revenue shortfall.
2. **Alzheimer's Disease Drug Costs**: The costs associated with the development and commercialization of Aduhelm, Biogen's controversial Alzheimer's disease drug, had a substantial impact on the company's earnings. The company recorded charges related to dropping Aduhelm, which negatively impacted earnings by 35 cents per share.
3. **Market Penetration Challenges**: Biogen faces challenges in market penetration for its Alzheimer's treatments due to difficulties in accessing neurologists and the uptake of newer drugs. These challenges are exacerbated by the competitive landscape and the need for significant pipeline catalysts.

In summary, Biogen's Q1 2024 earnings miss was primarily due to a decline in multiple sclerosis drug sales and the costs associated with its Alzheimer's disease drug, Aduhelm, along with market penetration challenges.