Acadia misses mark in Alzheimer’s but concludes phase 3 ‘absolutely worth’ pursuing

Biotech Acadia misses mark in Alzheimer’s but concludes phase 3 ‘absolutely worth’ pursuing By Nick Paul Taylor Sep 24, 2026 9:46am Acadia Pharmaceuticals Alzheimer's disease failed trials Biotech Acadia Pharmaceuticals’ phase 2 Alzheimer’s disease trial has missed its primary endpoint, but the company and analysts alike saw enough encouraging signals to support the continuation of a phase 3 program. San Diego-based Acadia generated the data in the first part of the phase 2/3 Radiant trial. Acadia is running the study to compare remlifanserin, a 5HT2A receptor inverse agonist, to placebo in patients with Alzheimer’s psychosis.

Remlifanserin, which is also called ACP-204, hits the same target as Acadia’s Nuplazid but is designed to be less prone to causing QT prolongation, a cardiac adverse event. In the phase 2 part of the Radiant trial, Acadia linked the 60-mg remlifanserin dose to a 12.6-point drop on an assessment of hallucinations and delusions at Week 6. The biotech reported a 10.4-point decline on placebo, resulting in a 0.26 effect size and a missed primary endpoint.

TD Cowen analysts named an effect size of 0.35 to 0.4 as the most likely outcome in a Sept. 15 note to investors. Acadia fell short of those expectations.

However, with the p-value coming in at 0.0603—just above the 0.05 statistical significance threshold—BMO Capital analysts characterized the result as a “near miss” in a note to investors. The analysts added that “some encouraging signals support future development.” Acadia CEO Catherine Owen Adams went further, saying she was “very encouraged by the results.” “We believe with the high unmet medical need in this population, the efficacy that we've seen so far ... as well as the safety and tolerability profile, that this molecule offers the potential for patients with Alzheimer's disease psychosis, and it is absolutely worth our investment to move this forward into the phase 3 trial,” Adams said on a conference call with investors to discuss the data.

Acadia linked the 60-mg dose to a 1.3-point reduction on a key secondary endpoint measuring symptom severity. The 0.9-point reduction on placebo resulted in a nominally significant advantage for the drug candidate on the endpoint. Remlifanserin could still produce a significant improvement in Alzheimer’s psychosis in the phase 3 part of the trial, BMO analysts said.

The drug demonstrated a favorable safety profile, according to Acadia, with rates of adverse events similar in the treatment and placebo groups. The rates of serious adverse events and discontinuations because of side effects were also similar. There was no signal of QT prolongation versus placebo, no deaths on remlifanserin and no evidence that the drug negatively impacts motor symptoms or cognition.

The absence of a QT signal shows an improvement over Nuplazid and potentially derisks safety for the phase 2 trial Acadia is running in Lewy body dementia psychosis, BMO analysts said. The analysts added that the absence of motor impairment remains critical for future development in Alzheimer’s psychosis, “where off-label dopamine agent use can lead to long-term motor impairment in some patients.” Acadia concluded that the safety and efficacy results justify further development of the 60-mg dose. Meanwhile, 30 mg of remlifanserin showed minimal activity, leading the biotech to drop the dose from its phase 3 plans.

The company is looking into “how to enrich the population for further enhancement through phase 3,” Adams said. Possible tweaks include refining the phase 3 enrollment criteria for modestly higher baseline psychosis, Elizabeth Thompson, Ph.D., head of research and development at Acadia, said on the call. Applying the tweaked criteria to the phase 2 data boosted the primary endpoint effect size to 0.33.

“We really are trying to get that balance between something that doesn't have a meaningful impact on enrollment but does have an opportunity to increase our overall potential phase 3 efficacy,” Thompson said. Acadia’s stock opened down 11% at $22.50 on Thursday from a Wednesday closing price of $25.43. Acadia Pharmaceuticals Alzheimer's disease failed trials Biotech Clinical Data