A 32-year-old man with schizophrenia has been on risperidone 6 mg daily for 8 months. He presents to the outpatient clinic with his wife, who reports that he has gained 12 kg over the past 6 months. On examination, his weight is 82 kg (BMI 28.5), fasting blood glucose is 118 mg/dL, and triglycerides are 210 mg/dL. He denies polydipsia or polyuria. His mental state is stable. Which of the following is the most appropriate next step in management?