Biogen said that the decision “will exclude almost all patients who may benefit.”

A controversial new drug used to treat Alzheimer’s will only be covered by Medicare if patients are in clinical trials. On Tuesday, the federal health insurer announced that only that population will be approved to receive Biogen’s  (BIIB) – Get Biogen Inc. Report Aduhelm cost-free.

But with the price of around $56,000 per patient per year, Aduhelm is also very expensive — Biogen said that the policy will “exclude almost all patients who may benefit.”

“We believe Alzheimer’s patients should have access consistent with other therapies with FDA accelerated approval,” Biogen said in a statement.

Approved by the U.S. Food and Drug Administration in June, the drug aducanumab is proving to be controversial in the medical community.

While some trials showed that it can slow the cognitive decline associated with Alzheimer’s, others have failed to do so or have even shown potential for harm. Many scientists criticized its speedy approval instead of awaiting for more conclusive findings.

As first reported by Reuters, the Centers for Medicare and Medicaid announced that the trials will help show how the drug works and whether it is effective in slowing Alzheimer’s. 

To qualify, patients need to not only be in the early stages of the disease and have a specific protein that the drug is meant to target, but also be in an official trial.

After news of the official coverage policy broke,  (BIIB) – Get Biogen Inc. Report shares fell by almost 8% in after-hours trading. Medicare’s proposal still needs to go through a a 30-day period of public comment, with a decision is expected to be finalized in April.