Depression (mood)

# Overview
In the fields of psychology and psychiatry, the terms depression or depressed refer to both expected and pathologically chronic or severe levels of sadness, perceived helplessness,  disinterest, and other related emotions and behaviours. The Diagnostic and Statistical Manual of Mental Disorders (DSM) states that a depressed mood is often reported as being: "depressed, sad, hopeless, discouraged, or 'down in the dumps'." In traditional colloquy, "depressed" is often synonymous with "sad," but both clinical and non-clinical depression can also refer to a conglomeration of more than one feeling.  Such a mixture can include (but is not limited to) anger, fear, anxiety, despair, guilt, apathy, and/or grief, in addition to what many people would describe as typical "sadness."
In a clinical setting, a depressed mood can be something a patient reports (a symptom), or something a clinician observes (a sign), or both.

# Determinants of mood
Depression can be the result of many factors, individually and acting in concert.

## Environment
Reactions to events, often a loss in some form, are perhaps the most obvious causes. This loss may be obvious, such as the death of a loved one, or having moved from one house to another (mainly with children), or less obvious, such as disillusionment about one's career prospects. Monotonous environments can be depressing. Merely painting a workplace can stimulate productivity. A lack of control of one's environment can lead to feelings of helplessness. Domestic disputes and financial difficulties are common causes of a depressed mood. Other causes of depression are climatic conditions, such as a rainy weather and a lack of sunlight, loneliness, and feelings that one isn't cared about by others.

## Internal psychological factors
Sometimes the depressed mood may relate more to internal processes or even be triggered by them. Pessimistic views of life or a lack of self-esteem can lead to depression. Illnesses and changes in cognition that occur in psychoses and dementias, to name but two, can lead to depression.

## Biological models of causation
These are varied but generally include hereditary, neurotransmitter, hormonal, illness and seasonal factors which are more fully discussed in the clinical depression article.

# Adaptive benefits of depression
While a depressed mood is usually seen as deleterious, it may have adaptive benefits. Of interest is the fact that physical illness tends to lead to depressive behavior and some diseases, such as influenza, are often accompanied by a degree of depression that seems out of proportion to the physical illness. A depressed mood is adaptive in illness in that it leads to the person resting and in general elicits care. Seasonal affective disorder may point to an atavistic link with behavior in hibernation.

## Biology
Biological influences of depression are varied, but can include hereditary, hormonal, and seasonal factors, stress, illness, neurotransmitter malfunction, and long-term exposure to dampness and mold and to aerosol exposure via the frequent use of air fresheners and other aerosols in the home,, all of which are more fully discussed in the major depressive disorder article.

# Depression as mechanism of adaptation
While a depressed mood is usually referred to (and perceived) as negative, it can sometimes be subtly beneficial in helping a person adapt to circumstance. For example, physical illness, such as influenza, can lead to feelings of psychological malaise and depression that seem, at first, only to compound an already unpleasant situation. However, the experience of depression, or feeling "down," often results in physical inertia, which leads to the compulsion to rest. The fleeting helplessness and immobility of the physically ill may also serve to elicit care from others.
From an evolutionary standpoint, some argue that depression could be at least partially related to atavistic fears that were originally based on real dangers. Paul Keedwell, in his book, How Sadness Survived: The Evolutionary Basis of Depression, suggests that, because "social support and interdependence were important features of the  ancestral environment," "the  group could have offered extra help to the depressed person until the condition resolved."  Further, "...a depressed person may change the attitudes of other people around him, making them more sympathetic to his needs and therefore giving him a long term  advantage."
Temporary depression, psychologist Thomas Moore, Ph.D., suggests, can, in some cases, not only "...provide a rest from the hyperactivity of the good times...," but can also be assigned value in the overall spectrum of human experience, and might enrich the ways in which members of a community relate to, and support, one another. In some cases, Moore says, "dark times  leave their mark and make you a person of insight and compassion." 

# Psychological disorders with depression
Episodes of depressed mood are a core feature of the following psychological disorders, as specified by the DSM-IV:
- Major depressive disorder
- Dysthymia
- Bipolar disorder
- Cyclothymia
- Schizoaffective disorder
- Seasonal affective disorder
- Adjustment disorder with depressed mood

# Mental disorders with depression
A depressed mood is usually a core feature of some mental disorders such as:
- manic depression (Bipolar disorder)
- clinical depression
- endogenous depression
- reactive or neurotic depression
- atypical depression
- psychotic depression
- seasonal affective disorder
- adjustment disorder with depressed mood
- Obsessive-Compulsive Disorder (O.C.D.) Can often lead to depression if left untreated

## Substances commonly used or promoted to treat depression (effective or not)
- Antidepressants
- Coffee
- Magnesium taurate
- Paxil
- Prozac
- Saint John's Wort
- Zoloft