In the first week, 500 mg of metformin was administered in the morning to the groups of metformin 500 mg/d and 1000 mg/d, and placebo was administered to the placebo group. In the second week, the dosage was revised to 500 mg of metformin in the morning and the placebo in the evening for the group of metformin 500 mg/d, 500 mg of metformin twice a day for the group of metformin 1000 mg/d, and placebo twice daily for the placebo group. For all patients, the clozapine dosage remained unchanged throughout the intervention. The recruited patients underwent physical and laboratory evaluations at week-4, week-8, and week-12.