Crazy that FDA fast-tracked the first novel drug for Alzheimer’s but now the agency has decided to convene a panel of independent experts to evaluate the drug’s safety and efficacy of Eli Lilly’s donanemab.

The decision is likely to surprise many Alzheimer’s experts, doctors and patients who had expected the medication would soon be on the market. The F.D.A.’s move was startling to the company, which had been planning for the agency to greenlight the drug during the first quarter of this year.

“We were not expecting this,” Anne White, an executive vice president of Lilly and president of its neuroscience division, said in an interview. She said that while the F.D.A. often calls on such independent advisory committees when it has questions about drugs, it was unusual to do so “at the end of the review cycle and beyond the action date that the F.D.A. had given us.”