Major depression is a common medical condition characterized by many physical and psychological symptoms, which may include profound sadness, loss of interest or pleasure in activities normally enjoyed and other symptoms that impair a person's ability to function.

Major depression is a type of mood disorder. Depression in all its forms is not "the blues" or occasional sadness or grief, which is a normal response to loss. Major depression is a persistent condition that interferes with a person's life over a period of at least two weeks.

Episodes of major depression may occur suddenly or gradually and usually last several months. It is common for episodes to recur, and, when depression is combined with other risk factors, suicide is a major risk.

The cause of depression is not known, but a number of advances have been made in identifying potential factors. Most likely a combination of genetic and environmental factors are involved. Major depression tends to run in families, and it may be triggered by severe stress (e.g., abuse, death of a loved one). It is more commonly diagnosed in women and people with chronic medical conditions.

Many people with symptoms of depression first visit their primary care physician for help. The physician should perform a physical examination to rule out possible physical causes of the symptoms. Afterward, a mental health evaluation may be performed by a physician or a mental health professional such as a psychologist, social worker or counselor.

To be diagnosed with major depression, a patient must show at least five of the nine primary symptoms, including altered mood or loss of interest or pleasure in normally pleasurable activities, and seriously altered sleep and/or appetite. These symptoms must occur most of the day, nearly every day, for at least two weeks and must be severe enough to cause distress or impair function.

People with mild cases of major depression may respond well with psychotherapy alone, whereas those with moderate to severe depression may require medication treatment (e.g., antidepressants). The outcome of treatment is generally best with a combination of psychotherapy and medication. In severe cases, where medication has not improved symptoms or when symptoms are life threatening, electroconvulsive therapy may be recommended.