Depression may be described as feeling sad, blue, unhappy, miserable, or down in the dumps. Most of us feel this way at one time or another for short periods.

True clinical depression is a mood disorder in which feelings of sadness, loss, anger, or frustration interfere with everyday life for a long period of time.

The exact cause of depression is not known. Many researchers believe it is caused by chemical imbalances in the brain, which may be hereditary or caused by events in a person's life.

Some types of depression seem to run in families, but depression can also occur in people who have no family history of the illness. Stressful life changes or events can trigger depression in some people. Usually, a combination of factors is involved.

Men and women of all ages, races, and economic levels can have depression. Depression can also occur in children and teenagers.

A number of factors can play a role in depression:

• Alcohol or drug abuse
• Life events or situations, such as:
  • Breaking up with a boyfriend or girlfriend, failing a class, illness or death in the family, or parents divorcing (for adolescents)
  • Childhood events, such as abuse or neglect
  • Divorce, death of a friend or relative, or loss of a job (for adults)
  • Social isolation (common in the elderly)
• Medical conditions such as hypothyroidism (underactive thyroid), medications (such as sedatives and high blood pressure medications), cancer, major illness, or prolonged pain
• Sleeping problems

See also: Adolescent depression