Acadia Pharmaceuticals Stock Drops After Mixed Alzheimer's Drug Trial Data

Acadia Pharmaceuticals Inc. (NASDAQ: ACAD) shares declined by 6% after the company released mixed results from its Phase 2 RADIANT study for remlifanserin, a potential treatment for Alzheimer’s disease psychosis. The drug candidate narrowly failed to meet its primary objective but showed a statistically significant improvement on a key secondary endpoint.

Trial Results in Detail

The study evaluated two doses of remlifanserin against a placebo. According to the company's announcement, the trial's primary endpoint, a measure of psychosis symptoms known as SAPS H+D, was narrowly missed with a p-value of 0.0603, just outside the conventional threshold for statistical significance.

However, the drug did achieve success on its key secondary endpoint, the Clinical Global Impression-Severity (CGI-S-ADP), which measures the overall severity of the condition. This endpoint reached nominal significance with a p-value of 0.0077. The positive results were driven by the 60 mg dose, while the 30 mg dose showed minimal improvement over the placebo.

Safety Profile and Path Forward

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Despite the mixed efficacy results, remlifanserin demonstrated a favorable safety profile. The rates of adverse events, serious adverse events, and discontinuations were similar to the placebo group. Notably, there was no signal of QT prolongation—a potential heart rhythm issue—and no negative impact on motor skills or cognition.

Based on these findings, Acadia plans to continue with its two ongoing Phase 3 studies of remlifanserin for Alzheimer's disease psychosis. The company will, however, remove the ineffective 30 mg dosage arm from the program. This decision suggests that while the primary endpoint miss is a setback, the positive secondary results and strong safety data provide the company with a viable, albeit more complex, path forward.

Context for Investors

The market's negative reaction reflects the increased risk and uncertainty following the failure to achieve the primary goal, which is typically the most critical measure for regulatory approval. Investors will be closely watching for more detailed data, which Acadia plans to present at the Clinical Trials on Alzheimer’s Disease conference in Boston from November 16-19, 2026. The company is also investigating remlifanserin in a separate Phase 2 study for psychosis associated with Lewy body dementia.