This case study explores the therapeutic application and associated challenges of using carbamazepine as a mood stabilizer in the management of schizoaffective disorder. The patient, a 42-year-old male with a history of schizoaffective disorder, exhibited acute manic symptoms exacerbated by substance use and non-compliance with medication. The introduction of carbamazepine initially showed promise in stabilizing mood and reducing psychotic symptoms. However, the treatment course was complicated by a significant adverse dermatological reaction. This necessitated a switch to valproic acid, which was better tolerated. The case underscores the importance of careful monitoring and readiness to adjust treatment in response to carbamazepine-induced side effects. This study highlights the critical need for individualized treatment plans and emphasizes the role of pharmacogenetic testing in predicting adverse drug reactions, ensuring safer and more effective management of psychiatric conditions.