Depressive disorders affect approximately 19 million American adults. The suffering endured by people with depression and the lives lost to suicide attest to the great burden of this disorder on individuals, families, and society. Improved recognition, treatment, and prevention of depression are critical public health priorities. The National Institute of Mental Health (NIMH), the world's leading mental health biomedical organization, conducts and supports research on the causes, diagnosis and treatment of depression and the prevention of depression.

Evidence from neuroscience, genetics, and clinical investigation demonstrate that depression is a disorder of the brain. Modern brain imaging technologies are revealing that in depression, neural circuits responsible for the regulation of moods, thinking, sleep, appetite, and behavior fail to function properly, and that critical neurotransmitters - chemicals used by nerve cells to communicate - are out of balance. Genetics research indicates that vulnerability to depression results from the influence of multiple genes acting together with environmental factors. Studies of brain chemistry and of mechanisms of action of antidepressant medications continue to inform the development of new and better treatments.

In the past decade, there have been significant advances in our ability to investigate brain function at multiple levels. NIMH is collaborating with various scientific disciplines to effectively utilize the tools of molecular and cellular biology, genetics, epidemiology, and cognitive and behavioral science to gain a more thorough and comprehensive understanding of the factors that influence brain function and behavior, including mental illness. This collaboration reflects the Institute's increasing focus on "translational research," whereby basic and clinical scientists are involved in joint efforts to translate discoveries and knowledge into clinically relevant questions and targets of research opportunity. Translational research holds great promise for disentangling the complex causes of depression and other mental disorders and for advancing the development of more effective treatments.

Symptoms and Types of Depression

Symptoms of depression include a persistent sad mood; loss of interest or pleasure in activities that were once enjoyed; significant change in appetite or body weight; difficulty sleeping or oversleeping; physical slowing or agitation; loss of energy; feelings of worthlessness or inappropriate guilt; difficulty thinking or concentrating; and recurrent thoughts of death or suicide. 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.

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.