Clinical depression is a state of sadness or melancholia that has advanced to the point of being disruptive to an individual’s social functioning and/or activities of daily living. The diagnosis may be applied when an individual meets a sufficient number of the symptomatic criteria for the depression spectrum as suggested in the DSM-IV-TR or ICD-9/10. An individual is often seen to suffer from what is termed a “clinical depression” without fully meeting the various criteria advanced for a specific diagnosis on the depression spectrum. There is an ongoing debate regarding the relative importance of genetic or environmental factors, or gross brain problems versus psychosocial functioning.
Although a mood characterized by sadness is often colloquially referred to as depression, clinical depression is something more than just a temporary state of sadness. Symptoms lasting two weeks or longer, and of a severity that begins to interfere with typical social functioning and/or activities of daily living, are considered to constitute clinical depression.
Clinical depression was originally considered to be a “chemical imbalance” in transmitters in the brain, a theory based on observations made in the 1950s of the effects of reserpine and isoniazid in altering monoamine neurotransmitter levels and affecting depressive symptoms . Subsequent antidepressants have also been found to alter monoamine levels, particularly of serotonin and noradrenaline . Despite a growing body of evidence suggesting otherwise, it is still a commonly held belief that depression is only a chemical imbalance. This idea is often promoted in pharmaceutical advertising, and perpetuated in everyday discussions. Despite this reliance on “common wisdom”, recent research and commentary has begun to address depression as an issue broader than this.
Clinical depression affects about 16% of the population on at least one occasion in their lives. The mean age of onset, from a number of studies, is in the late 20s. About twice as many females as males report or receive treatment for clinical depression, though this imbalance is shrinking over the course of recent history; this difference seems to completely disappear after the age of 50 – 55, when most females have passed the end of menopause. Clinical depression is currently the leading cause of disability in the US as well as other countries, and is expected to become the second leading cause of disability worldwide (after heart disease) by the year 2020, according to the World Health Organization.
On a historical note, the modern idea of depression appears similar to the much older concept of melancholia. The name melancholia derives from ‘black bile’, one of the ‘four humours’ postulated by Galen.
The Ebers papyrus (ca 1550 BC) contains a short description of clinical depression. Though full of incantations and foul applications meant to turn away disease-causing demons and other superstition, it also evinces a long tradition of empirical practice and observation.