Studies on aducanumab were halted earlier this year because the drug didn't appear to be effective. But the new results suggest it's effective at a high dose, the Associated Press reported.
The findings were presented at an Alzheimer's conference in San Diego.
However, some experts say that changes during the study and unusual analyses make the results difficult to interpret and the risks and benefits of the drug unclear, the AP reported.
"I don't see how you can conclude anything other than that another trial needs to be done," said Dr. David Knopman of the Mayo Clinic, who is a member of an FDA panel likely to review the drug.
He's not likely to participate in such a review because he was involved in one of the studies, the AP reported.
Aducanumab -- being developed by U.S. company Biogen and Japanese company Eisai -- is designed to clear harmful plaques, or protein clumps, from the brain.