Depression is a major public health problem and a leading predictor of functional disability and mortality. The annual economic consequences of depression have been estimated at 83 billion dollars in the United States  and 118 billion euro in Europe . Optimal depression treatment improves outcomes for most patients.
Although most adults with clinically significant depression never see a mental health professional, they often see a primary care physician. Yet substantial numbers of depressed primary care patients remain undiagnosed or under-treated, reflecting attitudes and practices of physicians, patients, families, and health care systems. A systematic review of 36 studies found that non-psychiatric physicians missed the diagnosis of depression in over one half of patients seen , although these findings should be interpreted with recognition of the difference between primary care and psychiatric practice in the severity of depression, the complexity of diagnosing and treating depression in the context of other chronic medical illness, and the primary care approach to diagnosis over several office visits.
This topic will focus on the clinical features and diagnosis of depression. The epidemiology, pathogenesis, treatment, and prognosis of depression in adults and elderly patients are discussed separately:
●(See "Unipolar depression in adults: Epidemiology, pathogenesis, and neurobiology".)
●(See "Unipolar major depression in adults: Choosing initial treatment".)