Schizophrenia Treatment Fails to Meet Primary Endpoint in Phase 3 Clinical Studies


Although ulotaront was well-tolerated, results for patients treated with it were not superior to those for patients treated with placebo.

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Results from 2 phase 3 clinical studies show that a drug under investigation as a treatment for schizophrenia has failed to meet its primary endpoint.

The drug, ulotaront, is a trace amine-associated receptor 1 (TAAR1) agonist with 5-HT1A agonist activity administered once daily to adults with schizophrenia. The Developing Innovative Approaches for Mental Disorders (DIAMOND) 1 and DIAMOND 2 multicenter, randomized, double-blind, parallel-group, fixed-dose clinical studies evaluated the safety, efficacy, and tolerability of ulotaront compared to placebo over the course of 6 weeks. Although the drug was shown to be largely safe and well-tolerated by patients in both studies, the results for ulotaront were not superior to placebo in either study.1

DIAMOND 1 compared ulotaront (50 mg/day and 75 mg/day) to placebo in 435 acutely psychotic patients. Although results showed a reduction in the Positive Negative Syndrome Scale (PANSS) total score over time, patients treated with ulotaront did not show statistically significant improvement compared to patients treated with placebo (least squares [LS] mean: -16.9 in ulotaront 50 mg/day and -19.6 in ulotaront 75 mg/day compared to -19.3 in patients treated with placebo).1

DIAMOND 2 compared higher doses of ulotaront (75 mg/day and 100 mg/day) to placebo in 464 acutely psychotic patients. DIAMOND 2 found larger mean deductions in the PANSS total score from baseline, but no statistically significant improvement in comparison to placebo (LS mean: -16.4 in ulotaront 75 mg/day and -18.1 in ulotaront 100 mg/day compared to -14.3 in patients treated with placebo).1

“Sumitomo Pharma and our collaborator Otsuka Pharmaceutical have done preliminary analyses of the data, and we believe that a high placebo response may have masked the therapeutic effect of this innovative molecule,” said Hiroshi Nomura, representative director, president, and CEO of Sumitomo Pharma, in a press release.

“High placebo responses, like those seen in DIAMOND 1 and DIAMOND 2, are well documented in psychiatric clinical studies. The placebo response in DIAMOND 1 was particularly high. These studies were conducted throughout the COVID-19 pandemic, and initial analyses of these data suggest an impact of COVID-19 on the placebo responses that were seen. We continue to work closely with Otsuka and analyze the data to determine our next steps and plan to discuss with the US FDA how to proceed based on these results.”


1. Sumitomo Pharma and Otsuka announce topline results from phase 3 DIAMOND 1 and DIAMOND 2 clinical studies evaluating ulotaront in schizophrenia. Sumitomo Pharma. News release. July 31, 2023. Accessed July 31, 2023.

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