IntroductionThe aim of this study was to analyze the effectiveness of gabapentin administration to bipolar patients who had an incomplete response to other mood stabilizers.Subjects and methodsTwenty-two RDC bipolar 1 and II patients were assessed by means of the SADS and entered if they gave their consent to participate. All them had suffered from frequent relapses, subsyndromal features (mostly depressive) and incomplete response to other drugs. They all received open-label increasing doses of gabapentin until clinical response. The patients were assessed through the CGI-BP and a specific questionnaire at baseline and at 12 weeks of follow-up.ResultsSix out of the 22 patients dropped out for various reasons (four because of relapse, one because of side effects and one more because of poor compliance). Eight of the 16 patients that completed the 12-week follow-up showed at least two stages of improvement in the CGI. Using the last observation-carried forward analysis, the improvement was statistically significant for the depression subscale, and apparently related to social functioning, irritability and anxiety. Only one patient dropped out because of intolerance (mild rash). The mean dose of gabapentin was 1,310 mg/day.ConclusionGabapentin may be a useful drug for the add-on treatment of bipolar patients with poor response to other mood stabilizers. Gabapentin may improve depressive residual symptoms such as irritability, social withdrawal or anxiety. These results should be confirmed in randomized clinical trials.