Objective: The purpose of this study was to determine whether metformin promotes weight loss in overweight outpatients with chronic schizophrenia or schizoaffective disorder.
Method: In a double-blind study, 148 clinically stable, overweight (body mass index [BMI] ≥27) outpatients with chronic schizophrenia or schizoaffective disorder were randomly assigned to receive 16 weeks of metformin or placebo. Metformin was titrated up to 1,000 mg twice daily, as tolerated. All patients continued to receive their prestudy medications, and all received weekly diet and exercise counseling. The primary outcome measure was change in body weight from baseline to week 16.
Results: Fifty-eight (77.3%) patients who received metformin and 58 (81.7%) who received placebo completed 16 weeks of treatment. Mean change in body weight was -3.0 kg (95% CI=-4.0 to -2.0) for the metformin group and -1.0 kg (95% CI=-2.0 to 0.0) for the placebo group, with a between-group difference of -2.0 kg (95% CI=-3.4 to -0.6). Metformin also demonstrated a significant between-group advantage for BMI (-0.7; 95% CI=-1.1 to -0.2), triglyceride level (-20.2 mg/dL; 95% CI=-39.2 to -1.3), and hemoglobin A1c level (-0.07%; 95% CI=-0.14 to -0.004). Metformin-associated side effects were mostly gastrointestinal and generally transient, and they rarely led to treatment discontinuation.
Conclusions: Metformin was modestly effective in reducing weight and other risk factors for cardiovascular disease in clinically stable, overweight outpatients with chronic schizophrenia or schizoaffective disorder over 16 weeks. A significant time-by-treatment interaction suggests that benefits of metformin may continue to accrue with longer treatment. Metformin may have an important role in diminishing the adverse consequences of obesity and metabolic impairments in patients with schizophrenia.
Trial registration: ClinicalTrials.gov NCT00816907.