Olanzapine/Samidorphan in Young Adults With Schizophrenia, Schizophreniform Disorder, or Bipolar I Disorder Who Are Early in Their Illness: Results of the Randomized, Controlled ENLIGHTEN-Early Study.

Patients with early-phase schizophrenia or bipolar I disorder (BD-I) are at greater risk for antipsychotic-associated weight gain. This 12-week, randomized, double-blind study conducted between June 2017 and December 2021 evaluated weight effects of combination olanzapine and samidorphan (OLZ/SAM) versus olanzapine in early-phase illness. Young adults (16-39 years) with schizophrenia, schizophreniform disorder, or BD-I, < 4 years since symptom onset, body mass index < 30 kg/m, and < 24 weeks' cumulative antipsychotic exposure were randomized to OLZ/SAM (5-20/10 mg/d) or olanzapine (5-20 mg/d). Primary endpoint was percent change from baseline body weight at week 12. Secondary endpoints, tested hierarchically, were proportions of patients with ≥ 10% or ≥ 7% weight gain, waist circumference change, and Clinical Global Impressions-Severity (CGI-S) change. Of 428 patients (OLZ/SAM, n = 213; olanzapine, n = 215), 408 had ≥ 1 postbaseline weight assessment and were analyzed. Percent weight change was significantly lower with OLZ/SAM versus olanzapine (4.91% vs 6.77%; least-squares mean [LSM] [SE] difference, -1.87% [0.75];  = .012). Although fewer patients treated with OLZ/SAM had ≥ 10% weight gain, the difference was not statistically significant versus olanzapine (21.9% vs 30.4%, respectively; OR = 0.64; 95% CI  0.39 to 1.05); hierarchical testing precluded further statistical evaluation of secondary endpoints. Proportions of patients with ≥ 7% weight gain (33.1% vs 44.8%; OR = 0.61, 95% CI = 0.39 to 0.94) and waist circumference change (2.99 vs 3.90 cm; LSM [SE] difference, -0.92 cm [0.58]; 95% CI = -2.06 to 0.22) favored OLZ/SAM. LSM (SE) CGI-S change with OLZ/SAM was -0.82 (0.06). OLZ/SAM and olanzapine had similar safety profiles, including small, similar metabolic parameter changes. In patients with early-phase schizophrenia, schizophreniform disorder, or BD-I, OLZ/SAM treatment resulted in less weight gain versus olanzapine. ClinicalTrials.gov identifier: NCT03187769.