To evaluate the effect of metformin treatment on the risperidone-induced body weight gain in patients.

In a 12-weeks, double-blind, placebo controlled, randomized trial between October 2006 and October 2007 which was conducted in the Child and Adolescent Psychiatric Consultation Center of Isfahan University of Medical Sciences, 49 patients were entered the study with schizophrenia diagnosis. Then metformin (500 mg bid) or placebo was administrated with risperidone (6 mg) for the patients. Weight, height, and body mass index BMI were measured at the beginning, at 4 weeks, and at 12 weeks of the study. Changes in weight and BMI were evaluated by using repeated measures analysis of variance.

Seventeen patients were excluded from the study. Repeated measure analysis of variances showed a significant difference between weight and BMI in both metformin (p < 0.001, p < 0.015) and placebo group (p < 0.013, p < 0.005).

Metformin treatment did not show a significant effect to control the body weight of patients after 12 weeks.