Depression is a mental health disorder characterized by persistently depressed mood or loss of interest in activities, causing significant impairment in daily life.

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Possible causes include a combination of biological, psychological, and social sources of distress. Increasingly, research suggests these factors may cause changes in brain function, including altered activity of certain neural circuits in the brain.

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The persistent feeling of sadness or loss of interest that characterizes major depression can lead to a range of behavioral and physical symptoms. These may include changes in sleep, appetite, energy level, concentration, daily behavior, or self-esteem. Depression can also be associated with thoughts of suicide.

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The mainstay of treatment is usually medication, talk therapy, or a combination of the two. Increasingly, research suggests these treatments may normalize brain changes associated with depression.

Common diagnosis-More than 3 million US cases per year.