The US Food and Drug Administration declined to grant accelerated approval to an experimental Alzheimer’s drug, donanemab, and requested additional data from Eli Lilly and Company, the drug maker.

The company, which announced the development on Thursday, plans to file Phase 3 clinical trial data later this year for a traditional FDA approval.

The findings in a previous Phase 2 trial, published in May in the New England Journal of Medicine, suggested that treatment with donanemab could lead to “modestly less cognitive and functional decline” in patients with early Alzheimer’s disease, but the drug was associated with some adverse events, such as cerebral swelling or effusions, which were mostly asymptomatic.

In that trial, the researchers looked at the drug’s impact on the buildup of amyloid beta plaque and tau proteins, which are considered hallmarks of Alzheimer’s disease.