Subtypes of bipolar disorder

The 2 predominant subtypes of bipolar disorder are bipolar I and bipolar II. There is debate about whether it is worthwhile to distinguish between bipolar I and bipolar II disorder but international consensus favours using the distinction.

Bipolar I disorder is characterised by at least one manic episode, usually accompanied by depressive episodes, that are not better explained by another disorder. Symptoms cause clinically significant distress or functional impairment.

Bipolar II disorder is characterised by hypomanic and depressive episodes that are not better explained by another disorder. The depressive episodes cause clinically significant distress or functional impairment.

Other subtypes of bipolar disorder (eg cyclothymic disorder, substance or drug-induced bipolar disorder) are not discussed in these guidelines.