What happened Shares of Biogen (NASDAQ: BIIB) were sinking 9.5% as of 10:48 a.m. ET on Wednesday. The decline came after the Centers for Medicare and Medicaid Services (CMS) on Tuesday released its proposed National Coverage Determination (NCD) for Biogen's Alzheimer's disease drug Aduhelm. The proposed NCD would only cover Aduhelm for Medicare beneficiaries enrolled in clinical trials. So what Biogen had hoped that CMS would decide to provide full coverage for Aduhelm with Medicare beneficiaries. In the company's third-quarter conference call, chief financial officer Michael McDonnell said that Biogen expected revenue for the drug to especially pick up with a positive NCD decision this year. The revenue prospects for Aduhelm now appear to be in serious jeopardy. The steep sell-off for the biotech stock reflects this more-negative outlook. Image source: Getty Images. So why didn't CMS opt to provide more extensive coverage for Aduhelm, which won Food and Drug Administration (FDA) accelerated approval in 2020? CMS Administrator Chiquita Brooks-LaSure said in a press release, "CMS has proposed an evidence-based coverage policy after experts reviewed all relevant available evidence and feedback received from stakeholders." This NCD decision reflects the ongoing controversy over the FDA's approval of Aduhelm. Many in the healthcare community believe that the clinical data for the drug didn't support a positive approval decision. Unsurprisingly, Biogen disagreed vehemently with the CMS decision. The company issued a press release that stated, "Alzheimer's patients and their families deserve to have choice and access to FDA-approved treatments." Now what This story isn't over yet. The NCD is only a draft proposal. The agency will accept public comments for 30 days. CMS expects to announce its final decision by April 11. 10 stocks we like better than BiogenWhen our award-winning analyst team has a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* They just revealed what they believe are the ten best stocks for investors to buy right now... and Biogen wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of January 10, 2022 Keith Speights has no position in any of the stocks mentioned. The Motley Fool recommends Biogen. The Motley Fool has a disclosure policy.Source