ACADIA Pharmaceuticals' (ACAD) shares dropped 10% pre-bell after it reported that its phase 2 RADIANT study of remlifanserin for Alzheimer's disease psychosis narrowly missed its primary endpoint.

The primary endpoint was the change from baseline in the Scale for the Assessment of Positive Symptoms-Hallucinations and Delusions subscales at week six.

The study showed the 60 mg dose achieved nominal statistical significance on the key secondary Clinical Global Impression-Severity for Alzheimer's Disease Psychosis endpoint, while the 30 mg dose showed minimal improvement across endpoints versus placebo.

Across both doses, the rates of adverse events, serious adverse events, and discontinuations due to adverse events were similar to placebo.

The company said it plans to continue enrolling its two ongoing phase 3 studies evaluating remlifanserin in Alzheimer's disease psychosis, while amending the phase 3 program to remove the 30 mg dosage arm.

It also said remlifanserin is currently being investigated in another phase 2 study for Lewy body dementia psychosis.