What Is It?

Major depression is an illness that usually causes severe and persistent low mood – sadness or a sense of despair. It is considered a mood disorder. The mood change can also appear as irritability or the person may not be able to take pleasure in activities that usually are enjoyable.

Major depression is more than just a passing blue mood, a "bad day" or temporary sadness over a specific event. The mood changes that come with major depression last for at least two weeks and usually much longer.

A variety of symptoms usually accompany the mood change, and the symptoms can vary significantly between different people. Many people with depression also have anxiety and tend to worry more about their physical health. They may have problems in their relationships and may function less well at work. Sexual functioning may be a problem. People with depression are more likely to abuse alcohol or other substances.

Depression probably involves chemicals called neurotransmitters that carry messages between brain cells. Changes in some hormones may play a role in depression. An episode of depression can be triggered by a stressful life event, such as the death of a loved one. But in many cases, depression does not appear to be related to a specific event.

Major depression may occur just once in a person's life or may return periodically throughout life. Some people who have repeated episodes of major depression also have a long pattern of a milder depressed mood called dysthymia. When major depression alternates with periods of great exuberance and energy, the illness is called bipolar disorder. If a woman has a major depressive episode within a month after delivering a baby, it is called postpartum depression. Depression also can occur mainly during the winter months. This condition is called seasonal affective disorder, or SAD.

Episodes of depression can occur at any age. Depression affects women twice as often as men. People who have a family member with major depression are more likely to develop depression or drinking problems.