- Introduction: Epidemiologic studies have suggested that consumption of cold water fish oils may have some protective function against depression. This proposition is supported by a series of biochemical and pharmacologic studies that have suggested that fatty acids may modulate neurotransmitter metabolism and cell signal transduction in humans and that abnormalities in fatty acid and eicosanoid metabolism may play a causal role in depression. Aware of the critical need for antidepression treatments that might not carry the risk of precipitating a manic episode in bipolar patients, we decided to conduct an open-label add-on trial of eicosapentaenoic acid (EPA) in bipolar depression. Method: Twelve bipolar I outpatients with depressive symptoms diagnosed by DSM-IV were treated with 1.5 to 2 g/day of the omega-3 fatty acid EPA for up to 6 months. The study was conducted between September 2001 and January 2003. Results: Eight of the 10 patients who completed at least 1 month of follow-up achieved a 50% or greater reduction in Hamilton Rating Scale for Depression scores within 1 month. No patients developed hypomania or manic symptoms. No significant side effects were reported. Limitations: This study is limited both by the open-label design and by the small sample size. As in all previous reported studies, patients in this study were treated in an outpatient setting, so that the most severely depressed bipolar patients (requiring hospitalization) are not represented. Conclusions: Although the ultimate utility of omega-3 fatty acids in bipolar depression is still an open question, we believe that these initial results are encouraging, especially for mild to moderate bipolar depression, and justify the continuing exploration of its use.