A pilot trial of adjunctive gabapentin in the treatment of bipolar disorder.

Several antiepileptic drugs (AEDs) have documented efficacy in the manic phase of bipolar disorder. To investigate the efficacy, tolerability, and safety of the new AED, gabapentin, in mania, we treated nine consecutive outpatients with bipolar I or II disorder by DSM-IV criteria who were experiencing hypomanic, manic, or mixed states inadequately responsive to standard mood stabilizers with open-label, adjunctive gabapentin. Response of manic symptoms was assessed monthly as none, minimal, moderate, or marked. Of the nine patients, seven displayed a moderate or marked reduction in manic symptoms by 1 month after addition of gabapentin, and an additional patient displayed moderate improvement after 3 months. Of these eight patients, six displayed continued antimanic responses for follow-up periods ranging from 1 to 7 months. Side effects were most commonly neurological, mild, and transient. Adjunctive gabapentin may have antimanic and mood-stabilizing effects in some patients with bipolar disorder and is generally well tolerated. Controlled studies of gabapentin in bipolar disorder appear to be warranted.