File:Melencolia I (Durero).jpg

Albrecht Dürer's engraving Melencolia I, ca. 1514

Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being.[1] Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless. They may lose interest in activities that once were pleasurable, experience overeating or loss of appetite, or problems concentrating, remembering details or making decisions; and may contemplate or attempt suicide. Insomnia, excessive sleeping, fatigue, loss of energy, or aches, pains or digestive problems that are resistant to treatment may be present.[2]

Illnesses featuring depression

Psychiatric syndromes

A number of psychiatric syndromes feature depressed mood as a main symptom. Mood disorders are a group of disorders considered to be primary disturbances of mood. Within them, major depressive disorder (MDD), commonly called major depression, or clinical depression, is a condition where a person has at least two weeks of depressed mood or a loss of interest or pleasure in nearly all activities. Dysthymia is a state of chronic depressed mood, the symptoms of which do not meet the severity of a major depressive episode. People suffering bipolar disorder may also experience major depressive episodes.

Outside the mood disorders, dysthymia is also commonly a feature of borderline personality disorder. Adjustment disorder with depressed mood is a mood disturbance appearing as a psychological response to an identifiable event or stressor, in which the resulting emotional or behavioral symptoms are significant but do not meet the criteria for a major depressive episode.[3]

Non-psychiatric illnesses

Depressed mood can be the result of a number of infectious diseases and physiological problems. For example, mononucleosis, which can be caused by two different viral infections, often results in symptoms that mimic a depressive psychiatric disorder; and depression is often one of the early symptoms of hypothyroidism (reduced activity of the thyroid gland). For a discussion of non-psychiatric medical illnesses that can cause depressed mood, see Depression (differential diagnoses).


On October 1, 2010 the U.S. Centers for Disease Control and Prevention (CDC) released a report regarding the prevalence of current depression in the United States during 2006 and 2008 based on an analysis of Behavioral Risk Factor Surveillance System (BRFSS) survey data from 2006 and 2008. Current depression was defined as meeting BRFSS criteria for either major depression or "other depression" during the 2 weeks preceding the survey. The report summarizes the results of that analysis, which indicated that, among 235,067 adults (in 45 states, the District of Columbia [DC], Puerto Rico, and the U.S. Virgin Islands), 9.0% met the criteria for current depression, including 3.4% who met the criteria for major depression. By state, age-standardized estimates for current depression ranged from 4.8% in North Dakota to 14.8% in Mississippi.[4]

Physiology or mechanism

Depression is associated with changes in substances in the brain (neurotransmitters) that help nerve cells communicate, such as serotonin, dopamine and norepinephrine. The levels of these neurotransmitters can be influenced by, among other things, physical illnesses, genetics, hormonal changes, medications, aging, brain injuries, seasonal/light cycle changes, and social circumstances.

A 2010 review suggests that the genes which control the body clock may contribute to depression.[5]


A full patient medical history, physical assessment, and thorough evaluation of symptoms helps determine the cause of the depression. Standardized questionnaires can be helpful such as the Hamilton Rating Scale for Depression,[6] and the Beck Depression Inventory.[7]

A doctor generally performs a medical examination and selected investigations to rule out other causes of symptoms. These include blood tests measuring TSH and thyroxine to exclude hypothyroidism; basic electrolytes and serum calcium to rule out a metabolic disturbance; and a full blood count including ESR to rule out a systemic infection or chronic disease.[8] Adverse affective reactions to medications or alcohol misuse are often ruled out, as well. Testosterone levels may be evaluated to diagnose hypogonadism, a cause of depression in men.[9]

Subjective cognitive complaints appear in older depressed people, but they can also be indicative of the onset of a dementing disorder, such as Alzheimer's disease.[10][11] Cognitive testing and brain imaging can help distinguish depression from dementia.[12] A CT scan can exclude brain pathology in those with psychotic, rapid-onset or otherwise unusual symptoms.[13] Investigations are not generally repeated for a subsequent episode unless there is a medical indication.

See also


  1. Sandra Salmans (1997). Depression: questions you have - answers you need. People's Medical Society. ISBN 9781882606146.
  2. "Depression". National Institute of Mental Health. 2009-09-23. Retrieved 2010-05-22.
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  4. "Current Depression Among Adults --- United States, 2006 and 2008" Morbidity and Mortality Weekly Report (MMWR) October 1, 2010, 59(38);1229-1235, accessed October 1, 2010
  5. Kennaway, David J. (2010). "Review: Clock genes at the heart of depression". Journal of Psychopharmacology (SagePub) 24 (5): 5–14. doi:10.1177/1359786810372980. PMC 2951587. PMID 20663803. Retrieved 2010-10-20. "In humans, single nucleotide polymorphisms in Clock and other clock genes have been associated with depression.".
  6. Zimmerman M, Chelminski I, Posternak M (2004 Sep). "A review of studies of the Hamilton depression rating scale in healthy controls: implications for the definition of remission in treatment studies of depression.". J Nerv Ment Dis 192 (9): 595–601. PMID 15348975.
  7. McPherson A, Martin CR (2010 Feb). "A narrative review of the Beck Depression Inventory (BDI) and implications for its use in an alcohol-dependent population". J Psychiatr Ment Health Nurs 17 (1): 19–30. doi:10.1111/j.1365-2850.2009.01469.x. PMID 20100303.
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Selected cited works

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