Acadia's Alzheimer's psychosis drug fails mid-stage trial

Acadia Pharmaceuticals announced that its experimental drug remlifanserin missed the primary goal of a Phase 2 trial for Alzheimer's disease psychosis, failing to show a statistically significant reduction in hallucinations and delusions. Despite the setback, Acadia plans to continue two Phase 3 trials using only the 60-milligram dose, citing positive secondary outcomes and a favorable safety profile. Following the news on September 24, 2026, Acadia's stock fell by double digits.

Phase 2 trial efficacy results

• ▪Acadia Pharmaceuticals announced on September 24, 2026, that its experimental drug remlifanserin missed the primary goal of a Phase 2 trial to reduce hallucinations and delusions in patients with Alzheimer's disease psychosis
• ▪In Acadia's Phase 2 trial for Alzheimer's disease psychosis, a 60-milligram once-daily dose of remlifanserin showed greater improvement than placebo but did not achieve statistical significance after six weeks, while a 30-milligram once-daily dose showed little improvement compared with placebo
• ▪Remlifanserin achieved statistical significance on a key secondary measure evaluating the overall severity of Alzheimer's disease psychosis symptoms during Acadia's Phase 2 trial

Remlifanserin safety

• ▪Acadia Pharmaceuticals reported on September 24, 2026, that the rates of serious side effects for patients receiving remlifanserin in the mid-stage study for Alzheimer's disease psychosis were similar to those seen with placebo
• ▪Acadia's Phase 2 trial for Alzheimer's disease psychosis showed that remlifanserin had rates of side effects and treatment discontinuations similar to placebo, with no apparent adverse effects on movement or cognitive function and zero reported deaths