- Bipolar I disorder: involves at least one manic or mixed episode. Most people experience depression as well.
- Bipolar II disorder: involves at least one episode of hypomania and an episode of depression.
- Cyclothymia: involves hypomania and mild symptoms of depression (not a full episode of depression) experienced most of the time over at least a two-year period.
- When bipolar disorder does not fit into the above categories: For example, a person may experience mild depressive or hypomanic symptoms that last less than the two years specified for cyclothymia. Another example is when a person has depressive episodes, but their symptoms of mood elevation are too mild or brief to be diagnosed as mania or hypomania.
How common is bipolar disorder?
About 1 in every 100 adults is likely to have bipolar I disorder. When including bipolar II disorder and the milder forms, the prevalence goes up to about 4 in every 100 adults.1
1. Merikangas KR, Pato M. Recent Developments in the Epidemiology of Bipolar Disorder in Adults and Children: Magnitude, Correlates, and Future Directions. Clin Psychol-Sci Pr 2009; 16(2): 121-133.