Depression is a psychoneurotic disorder characterized by lingering sadness, inactivity, and difficulty in thinking and concentration. A significant increase or decrease in appetite and time spent sleeping, feelings of dejection and hopelessness, and sometimes suicidal tendencies may also be present. It is one of the most common psychiatric conditions encountered, and affects up to 25 percent of women and 12 percent of men. Depression differs from grief, bereavement, or mourning, which are appropriate emotional responses to the loss of loved persons or objects.

Depression has many forms and is very responsive to treatment. Dysthymia, or minor depression, is the presence of a depressed mood for most of the day for two years with no more than two months' freedom from symptoms. Bipolar disorder (manic-depressive disorder) is characterized by recurrent episodes of mania and major depression. Manic symptoms consist of feelings of inflated self-esteem or grandiosity, a decreased need for sleep...