The mood disorders are diagnosed in adults, children and adolescents. Although the term depression is often used to describe a temporary state of mind, feeling, or attitude, the term mood disorders refers to specific psychopathological entities with the particular associated features. Major depressive disorder (MDD) is defined as follows: Either the depressed mood, or the loss of interest or pleasure in all, or almost all, activities, and associated symptoms, for a period of at least two weeks. The symptoms represent a change from previous functioning and are relatively persistent, that is, they occur for most of the day, nearly every day, during at least a two-week period. The associated symptoms includes appetite disturbance, change in weight, sleep disturbance, psychomotor agitation or retardation, decreased energy, feelings of worthlessness or excessive or inappropriate guilt, difficulty thinking or concentrating, and recurrent thoughts of death or suicidal ideation or attempts.