A 60-year-old Chinese American man is started on citalopram 20 mg for a first episode of MDD. After 2 weeks, he reports significant nausea, dizziness, and excessive sedation. His symptoms are consistent with dose-related side effects despite being on a standard starting dose. He has no hepatic or renal impairment. The PMHNP considers pharmacogenomic and cultural factors. What is the most appropriate clinical action?