Mood disorders are mental health disorders involving emotional disturbances consisting of long periods of excessive sadness (depression) or excessive joyousness or elation (mania). 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. Sadness may be psychologically beneficial because it enables people to withdraw from offensive or unpleasant situations, which may aid recovery.

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.

Did You Know... In the United States, about one of six people have depression severe enough to require medical attention.

Joyousness or elation, usually linked to success and achievement, can sometimes be a defense against depression or a denial of the pain of loss. People who are dying sometimes have brief periods of elation and restless activity, and some recently bereaved people may even become elated rather than grieve normally. In people predisposed to mood disorders, these reactions may be the prelude to mania.

A mood disorder is diagnosed when sadness or elation is overly intense and continues beyond what would be expected for a particular event. Unlike normal emotional reactions, depression and mania greatly impair the ability to function physically, socially, and at work.

Some mood disorders involve mainly depression. Depression is termed a unipolar disorder. Other mood disorders, termed bipolar disorders, involve episodes of depression alternating with episodes of mania. Mania without depression (called unipolar mania) is very rare.

About 17% of the U.S. population experience depression severe enough to require medical attention. Of these people, one third have long-lasting (chronic) depression, and many of the remainder continue to have episodes of depression separated by periods of normal mood (recurring depression). Nearly 4% of the U.S. population have a bipolar disorder.

Last full review/revision June 2008 by Jan Fawcett, MD