mental disorder characterized by dramatic changes or extremes of mood. Affective disorders may include manic (elevated, expansive, or irritable mood with hyperactivity, pressured speech, and inflated self-esteem) or depressive (dejected mood with disinterest in life, sleep disturbance, agitation, and feelings of worthlessness or guilt) episodes, and often combinations of the two. Persons with an affective disorder may or may not have psychotic symptoms such as delusions, hallucinations, or other loss of contact with reality.

In manic-depressive disorders (bipolar disorder), periods of mania and depression may alternate with abrupt onsets and recoveries. Depression is the more common symptom, and many patients never develop a genuine manic phase, although they may experience a brief period of overoptimism and mild euphoria while recovering from a depression. The most extreme manifestation of mania is violence against others, while that of depression is suicide. Statistical studies have suggested a hereditary predisposition to the disorder, which commonly appears for the first time in young adults.

Manic-depressive disorders were described in antiquity by the 2nd-century Greek physician Aretaeus Of Cappadocia and in modern times by the German psychiatrist Emil Kraepelin. The current term is derived from folie maniaco-mélancholique, which was introduced in the 17th century. See also manic-depressive psychosis (bipolar disorder).