- Objective: Anticonvulsant agents such as carbamazepine and valproate are alternatives to lithium in treating subjects with bipolar disorder. Topiramate (Topamax®), a new antiepileptic agent, is a candidate drug for bipolar disorder. We evaluated topiramate as adjunctive treatment for bipolar patients. Methods: Eighteen patients with DSM-IV bipolar I disorder [mania (n=12), hypomania (n=1), mixed episode (n=5), and rapid cycling (n=6)], and two subjects with schizoaffective disorder – bipolar type, resistant to current mood-stabilizer treatment were initiated on topiramate, 25 mg/day, increasing by 25–50 mg every 3–7 days to a target dose between 100 and 300 mg/day, as other medications were held constant for 5 weeks. The Young Mania Rating Scale (Y-MRS), Hamilton Depression Rating Scale (Ham-D), and Clinical Global Impression-Bipolar Version Scale (CGI-BP) were used to rate subjects weekly. Results: By 5 weeks, 12 (60%) subjects were responders, i.e., 50% reduction in the Y-MRS scores and a CGI of ‘much’ or ‘very much improved’. Three subjects were ‘minimally improved’, four showed no change, and one was ‘minimally worse’. Six subjects had parasthesia, three experienced fatigue, and two had ‘word-finding’ difficulties; in all cases, side effects were transient. All patients lost weight with a mean of 9.4 lb in 5 weeks, and a significant reduction in body mass index (BMI) occurred too. Conclusions: Topiramate appears to have efficacy for the manic and mixed phases of bipolar illness. Other preliminary data suggest antidepressant efficacy too. Among obese bipolar subjects, the weight loss potential of topiramate may be beneficial. If controlled trials confirm these initial results, topiramate may be a significant addition to the available treatments for bipolar disorder.