A psychiatric condition differentiated from normal sadness or bereavement by its duration and intensity. Referred to in the Diagnosticand Statistical Manual of Mental Disorders (fourth edition, text revision; DSM-IV-TR) as major depressive disorder (MDD), depression is characterized primarily by either chronically depressed mood quality or anhedonia and accompanied by various combinations of the following symptoms: lethargy or agitation, concentration difficulties, hopelessness, sleep/appetite disturbances, decreased self-worth, shame/guilt, and suicidality. MDD is most often recurrent but is highly treatable with a combination of psychotherapy and medication. Early treatment yields a more positive long-term prognosis. Significant evidence exists that MDD has a genetic component that interacts with environmental stresses and idiosyncratic personality and cognitive factors.