Effect of metformin on olanzapine-induced weight gain: A 12-week randomised open-label study

Abstract

Background: Olanzapine is an atypical antipsychotic used in schizophrenia and bipolar affective disorder, but it is associated with weight gain and metabolic syndrome. Metformin is known to decrease insulin resistance and abnormal glucose metabolism. Therefore, it is thought that metformin might prove useful in preventing weight gain induced by olanzapine. Hence, this study was undertaken to assess the effect of metformin on body weight, body mass index (BMI), waist and hip circumference, waist-to-hip ratio, and blood glucose levels in patients receiving olanzapine and to observe their adverse effects. Methods: Sixty-five patients with schizophrenia or bipolar mania were randomly assigned for 12 weeks of treatment with olanzapine 10 mg/day plus metformin 850 mg/day (n = 33) or olanzapine alone (n = 32). Body weight, BMI, waist circumference, hip circumference, and waist-to-hip ratio were measured at baseline, weeks 4, 8, and 12. Fasting plasma glucose was estimated at baseline and end of the study. Results: 59/65 (90.8%) patients completed the study. The body weight, BMI, waist circumference, hip circumference, and waist-to-hip ratio increased in both groups but it was relatively less in patients receiving metformin along with olanzapine. In patients who received olanzapine plus metformin, weight gain of more than 7% was observed in 43.3%, and 86.2% in those who received only olanzapine, the difference in this parameter was statistically significant (P = 0.001). Fasting plasma glucose had decreased significantly with olanzapine plus metformin at week 12. Conclusion: The metformin plus olanzapine group patients had relatively less weight gain compared to those who received only olanzapine.

Keywords

• atypical antipsychotics
• metformin
• olanzapine
• weight gain