Positive Phase 2 Topline Results: Remlifanserin for the Treatment of Alzheimer Disease Psychosis

Acadia Pharmaceuticals today announced topline results from the phase 2 portion of the ongoing RADIANT clinical trial program evaluating remlifanserin, an investigational, highly selective, 5-HT2A receptor inverse agonist, for the treatment of hallucinations and delusions associated with Alzheimer disease psychosis (ADP). These results will enable further phase 3 study of remlifanserin.¹

Once daily 60 mg remlifanserin met its primary endpoint of change from baseline in the Scale for the Assessment of Positive Symptoms-Hallucinations and Delusions subscales (SAPS-H+D), demonstrating a change of -12.6 vs a -10.4 change for placebo at week 6 with a standardized effect size of 0.26 (P=0.0603). For the key secondary endpoint, Clinical Global Impression – Severity (CGI-S-ADP), the 60 mg dose achieved a change from baseline of -1.3 vs a change of -0.9 for placebo at week 6, yielding a standardized effect size of 0.37 [P=0.0077 (nominal)]. On both efficacy measures, the difference in the 60 mg dose vs placebo increased through the 6-week treatment period. The 30 mg dose showed minimal improvement across endpoints compared to placebo. All analyses were performed in the pre-specified modified full analysis set population.

“The phase 2 RADIANT findings provide encouraging evidence that 60 mg once daily remlifanserin may have the potential to reduce hallucinations and delusions in patients with Alzheimer disease,” said Jeffrey Cummings, MD, ScD, the director of the Chambers-Grundy Center for Transformative Neuroscience, University of Nevada, Las Vegas. “This patient population has a significant need for an efficacious medication that is well tolerated, convenient to administer, and is compatible with the many concomitant medications commonly used by patients with Alzheimer disease. In particular, avoiding negative impacts on motor symptoms and cognition is encouraging, and such a medicine could be an important treatment option for patients.”

This news follows the Fast Track designation: Back in July 2026, the US Food and Drug Administration granted Fast Track designation to remlifanserin for the treatment of hallucinations and delusions associated with ADP.²

About RADIANT

RADIANT is a global, multi-center, randomized, double-blind, placebo-controlled, operationally seamless phase 2 and 3 clinical trial program evaluating remlifanserin for the treatment of hallucinations and delusions associated with ADP. The phase 2 portion of the program was designed to evaluate the efficacy, safety, and tolerability of remlifanserin at 60 mg and 30 mg once-daily doses compared with placebo. Patients who complete the study will have the option of participating in a long-term open-label extension study.

Safety Profile

In this study, across both doses, remlifanserin demonstrated a favorable safety profile, with rates of adverse events, serious adverse events, and discontinuations due to adverse events, that were similar to placebo. There was no signal of QT prolongation vs placebo. This dataset suggests no negative impact on motor symptoms or cognition. Additionally, there were no deaths in the remlifanserin treatment arms.

Next Steps

Based on these data, Acadia plans to continue enrolling its 2 ongoing phase 3 studies evaluating remlifanserin in ADP while implementing amendments to the phase 3 program, including removing the 30 mg dosage arm.

“We are pleased that the phase 2 RADIANT data support continuation of the phase 3 ADP program, with new insights helping us to refine the program for future regulatory success. These results provide valuable information regarding the efficacy, safety and tolerability of once daily remlifanserin in Alzheimer disease psychosis,” said Catherine Owen Adams, the chief executive officer of Acadia Pharmaceuticals. “We are excited about the potential of remlifanserin in this area of high unmet need, for which there are no currently approved therapies.”

Acadia will present detailed safety and efficacy results from the RADIANT phase 2 study in an oral presentation at the upcoming Clinical Trials on Alzheimer's Disease (CTAD) conference, taking place November 16-19, 2026 in Boston, MA.

Remlifanserin for Lewy Body Dementia Psychosis

Remlifanserin is currently being investigated in an additional phase 2 study to evaluate its efficacy, safety, and tolerability for the treatment of Lewy body dementia psychosis.

References

1. Acadia Pharmaceuticals announces phase 3 enabling topline results from phase 2 RADIANT study of remlifanserin for the treatment of Alzheimer’s disease psychosis (ADP). News release. September 24, 2026. Accessed September 24, 2026. https://www.financialcontent.com/article/bizwire-2026-9-24-acadia-pharmaceuticals-announces-phase-3-enabling-topline-results-from-phase-2-radiant-study-of-remlifanserin-for-the-treatment-of-alzheimers-disease-psychosis-adp

2. Acadia Pharmaceuticals receives FDA Fast Track designation for remlifanserin in Alzheimer's disease psychosis. News release. July 20, 2026. Accessed September 24, 2026. https://www.businesswire.com/news/home/20260720458854/en/Acadia-Pharmaceuticals-Receives-FDA-Fast-Track-Designation-for-Remlifanserin-in-Alzheimers-Disease-Psychosis