Evidence-based long-term treatment of bipolar II disorder.

Bipolar II disorder is a distinct, lifelong mental illness that affects at least 1.5 million people in the United States, is associated with a high incidence of comorbidity, and ends with completed suicide in 10% to 15% of diagnosed individuals. Bipolar II disorder is characterized by at least 1 major depressive episode with 1 or more hypomanic episodes, as opposed to manic or mixed episodes. While it is expected that there may be similarities in approaches to managing patients with bipolar I and bipolar II disorders, data suggest differential patient responses to pharmacologic treatments, supporting the need for research specifically in patients with bipolar II disorder. Despite the prevalence and severity of the disorder, a well-developed scientific database informing long-term treatment choices for bipolar II disorder as an illness differing from bipolar I disorder and major depressive disorder is virtually absent. A review of the limited and sometimes contradictory information stresses that more research is needed into prophylactic and maintenance treatment of bipolar II disorder.