The drug, donanemab, met all goals of the trial.
"These are the strongest phase 3 data for an Alzheimer's treatment to date," said Maria Carrillo, chief science officer for the Alzheimer's Association.
In the donanemab treatment group, Lilly said brain swelling, a known side effect of drugs of this type, occurred in 24% of the participants, with 6.1% experiencing symptoms.
In the Leqembi Phase 3 trial, the drug was associated with brain swelling in nearly 13% of its study participants.
It also said 47% of donanemab patients in the 18-month trial had no disease progression at 12 months, compared with 29% of the placebo group.