Mood disorders are mental health disorders that involve emotional disturbances consisting of long periods of excessive sadness (depression), excessive joyousness or elation (mania), or both. Depression and mania represent the two extremes, or poles, of mood disorders.
Mood disorders are sometimes called affective disorders. Affect (emphasis on the first syllable) means emotional state as revealed through facial expressions and gestures.
Sadness and joy are part of the normal experience of everyday life and differ from the depression and mania that characterize mood disorders. Sadness is a natural response to loss, defeat, disappointment, trauma, or catastrophe.
Grief or bereavement is the most common of the normal reactions to a loss or separation, such as the death of a loved one, divorce, or romantic disappointment. Usually, bereavement and loss do not cause persistent, incapacitating depression except in people predisposed to mood disorders.
A mood disorder is diagnosed when sadness or elation is overly intense, is accompanied by certain other typical symptoms, and impairs the ability to function physically, socially, and at work.
When only depression (see Depression) occurs, it is termed a unipolar disorder. Other mood disorders, termed bipolar disorders (see Bipolar Disorder (Manic-Depressive Illness)), involve episodes of depression alternating with episodes of mania. Mania without depression (called unipolar mania) is very rare.
About 30% of people report depression as one of their symptoms when they see their doctor. But fewer than 10% actually have severe depression. Nearly 4% of the U.S. population have a bipolar disorder.
Last full review/revision September 2014 by William Coryell, MD