Clinical depression occurs when these feelings, along with a set of additional symptoms, become intense, persist for several weeks, and interfere with academic, social, family, or occupational functioning. It is estimated that between 10 and 25 per cent of the general population will experience a least one debilitating episode of depression during the course of a lifetime. Depression may occur at any age, but appears to be a disorder of relatively early onset, with particular risk in early adulthood. The symptoms of depression usually develop over the course of days or weeks. Its duration is variable, with the average untreated episode lasting six months or more.
Most people experience a complete remission of their symptoms.
For others, however, the depression partially remits, becomes recurrent or is chronic. Typically, depression is very responsive to treatment. Of those who seek help, the majority are treated successfully. Clinically significant depression is more than the emotional experience of sadness. Mood symptoms interact with cognitive, behavioural and physical symptoms.