A disorder causing severe and persistent low mood. Other common symptoms include profound sadness, a sense of despair and a loss of pleasure for previously enjoyable activities. The diagnosis is made when mood changes and other symptoms of depression persist for at least 2 weeks. Major depression carries a risk of suicide if not appropriately treated. The cause of major depression is not known. 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 repeatedly.