A diagnosis of major depressive disorder (or unipolar major depression) is made if an individual has five or more of these symptoms during the same two-week period. Unipolar major depression typically presents in discrete episodes that recur during a person's lifetime.
Bipolar disorder (or manic-depressive illness) is characterized by episodes of major depression as well as episodes of mania – periods of abnormally and persistently elevated mood or irritability accompanied by at least three of the following symptoms: overly-inflated self-esteem; decreased need for sleep; increased talkativeness; racing thoughts; distractibility; increased goal-directed activity or physical agitation; and excessive involvement in pleasurable activities that have a high potential for painful consequences.
While sharing some of the features of major depression, bipolar disorder is a different illness that is discussed in detail in a separate NIMH publication.
Dysthymic disorder (or dysthymia), a less severe yet typically more chronic form of depression, is diagnosed when depressed mood persists for at least two years in adults (one year in children or adolescents) and is accompanied by at least two other depressive symptoms.
Many people with dysthymic disorder also experience major depressive episodes. While unipolar major depression and dysthymia are the primary forms of depression, a variety of other subtypes exist.
Extreme and Presistent
In contrast to the normal emotional experiences of sadness, loss, or passing mood states, depression is extreme and persistent and can interfere significantly with an individual's ability to function.In fact, a recent study sponsored by the World Health Organization and the World Bank found unipolar major depression to be the leading cause of disability in the United States and worldwide.
There is a high degree of variation among people with depression in terms of symptoms, course of illness, and response to treatment, indicating that depression may have a number of complex and interacting causes. This variability poses a major challenge to researchers attempting to understand and treat the disorder.
However, recent advances in research technology are bringing NIMH scientists closer than ever before to characterizing the biology and physiology of depression in its different forms and to the possibility of identifying effective treatments for individuals based on symptom presentation.
One of the most challenging problems in depression research and clinical practice is refractory – hard to treat – depression. While approximately 80 percent of people with depression respond very positively to treatment, a significant number of individuals remain treatment refractory.
Even among treatment responders, many do not have complete or lasting improvement, and adverse side effects are common. Thus, an important goal of NIMH research is to advance the development of more effective treatments for depression – especially treatment-refractory depression – that also have fewer side effects than currently available treatments.
