Patients will be randomly allocated into two groups (metformin and placebo group) using a computer-software. Fifteen PCOS patients will be treated with metformin at a dosage of 1700 mg daily (one tablet of 850 mg twice daily; metformin group), whereas other 15 PCOS will be treated with placebo tables (one tablet twice daily; placebo group). The duration of the treatment will be 12 months. Patients will be instructed to follow their usual diet and physical activity, and to use barrier contraception throughout the study. The length and the frequency of the menstrual cycles, and the adverse experiences (AEs) will be reported on a daily diary.