When the U.S. Food and Drug Administration approved Biogen Inc.’s controversial Alzheimer’s drug Aduhelm earlier this month without firm evidence that the drug helps patients, it created concern that other unproven treatments might follow. That scenario is already here.

Eli Lilly & Co. announced Thursday that it plans to file for accelerated approval for its experimental Alzheimer’s treatment donanemab this year based on its ability to clear amyloid brain plaques believed by some to cause the disease. That’s the same unprecedented justification and pathway the FDA used for Aduhelm. Lilly is clearly reacting to the agency’s shifted goalposts; in April, the company told investors it wouldn’t seek a quick approval because the regulator said there wasn’t enough data.

But that was the old FDA. It’s now possible that the agency might approve another medicine based on an unproven idea. Lilly shareholders seem to think so — the company’s shares rose 8% on Thursday. And yet, although approval would boost Lilly’s revenue prospects, it would compound the mistakes of the Aduhelm decision and further damage future Alzheimer’s research and America’s health budget.

Amyloid plaque removal has failed to help patients in many previous trials, and using it as the sole basis for approval of Biogen’s treatment was a surprise. The FDA released guidance on Alzheimer’s drugs in 2018 rejecting such secondary measures because of scientific uncertainty. A panel of external experts asked to evaluate Biogen’s drug in November were told that the agency wasn’t considering that option. But when the group voted that the contradictory evidence from Biogen’s trials didn’t support approval, the FDA found a new way forward. Three members of the expert panel resigned in protest.

The FDA can right the ship. By waiting a bit and conducting a public evaluation of the evidence for amyloid with more data, the agency could reset expectations and its standards instead of opening the barn door wider.

Max Nisen is a Bloomberg Opinion columnist covering biotech, pharma and health care. He previously wrote about management and corporate strategy for Quartz and Business Insider.