Course of Depression
Depressive symptoms typically develop over 2 or 3 weeks before the onset of a major depressive episode, during which time a person becomes anxious at the loss of concentration and energy. Untreated depressive episodes can last from 6 to 18 months, but average is about 8 months. Treated episodes typically last from 6 weeks to 3 months. In treated depression, episodes tend to return prematurely when antidepressants are not taken for the full indication.
Depression often is a chronic disease that relents periodically; depressed people may experience 1 to 2 years of mental health, without symptoms, between episodes. Approximately 60 percent of depressed people experience a second episode, and there is a 20 percent chance for chronic depression. Depressed people suffer an average of five or six episodes during a 20-year period, with an increased risk for recurrence in men. Given the average duration of an episode, chronic depression can affect about one-quarter of a person's lifetime.
Some people with depression develop episodes of mania as well as depression. This happens in roughly 7 percent of casesusually between the ages of 30 and 3commonly after four or five depressive episodes. It results in a diagnosis of bipolar disorder, rather than depression because the diagnostic criteria for recurrent major depression dictate the absence of mania.
Bipolar disorder may develop as a reaction to antidepressant medication, as the symptoms of people with bipolar behavior are similar to the side effects of antidepressant medication. These similarities include oversleeping and psychomotor retardation. A family history of bipolar disorder may also play a role.