A depression, if it is not primarily a reaction to a life event, is called in psychiatry a major depressive disorder (MDD). It is a condition characterized by at least two weeks of low mood that is present across most situations. It is often accompanied by low self-esteem, loss of interest in normally enjoyable activities, low energy, and psychological pain without a clear cause. There may also be false beliefs and – in the more severe cases – acoustic or visual hallucinations. Major depression needs to be differentiated from sadness. Depression often actually means the subjective absence of feelings, such as sadness. Patients often cannot feel themselves anymore as before, which can ause additional anxiety.
Another form is the reactive depression, which occurs as part of a number of conditions, such as post-traumatic stress disorder (PTSD). I discuss these forms of depressions within the articles on these conditions. In the following I want to focus on the depression which is not primarily a part of these conditions, the major depression.
Major depressive disorder can negatively affects a person’s family, work or school life, sleeping or eating habits, and general health. Between 2-7% of adults with major depression die by suicide  and up to 60% of people who die by suicide had depression or another mood disorder .
Some people have periods of depression separated by years in which they are normal while others nearly always have symptoms present. The first line of treatment is a combination of psychotherapy and medication. I will get back to some common antidepressants below. This combination has allowed most patients to live normal lives and in the vast majority leads to a significantly higher quality of life.
The cause is believed to be a combination of genetic, environmental, and psychological factors.  Risk factors include a family history of the condition, major life changes, certain medications, chronic health problems, and substance abuse.   About 40% of the risk appears to be related to genetics. 
Major depressive disorder affected approximately 253 million (3.6%) of people in 2013.  The percentage of people who are affected at one point in their life varies from 7% in Japan to 21% in France.  Lifetime rates are higher in the developed world (15%) compared to the developing world (11%). 
Depression causes the second most years lived with disability after low back pain. 
The most common time of onset is in a person in their 20s and 30s. Females are affected about twice as often as males.
Is there a depression?
Major depression significantly affects a person’s family and personal relationships, work or school life, sleeping and eating habits, and general health.  Its impact on functioning and well-being has been compared to that of other chronic medical conditions such as diabetes.
A person having a major depressive episode usually exhibits a very low mood, which pervades all aspects of life, and unhedonia, the inability to experience pleasure in activities that were formerly enjoyed. Depressed people may be preoccupied with, or ruminate over, thoughts and feelings of worthlessness, inappropriate guilt or regret, helplessness, hopelessness, and self-hatred. 
In severe cases, depressed people may have symptoms of psychosis. These symptoms include delusions or, less commonly, hallucinations, usually unpleasant.
Other symptoms of depression include
- poor concentration and memory
- withdrawal from social situations and activities
- reduced sex drive, irritability,
- and thoughts of death or suicide (which requires immediate professional help).
Insomnia is a common symptom. In the typical pattern, a person wakes very early and cannot get back to sleep. Hypersomnia, or oversleeping, can also happen. Some antidepressants may also cause insomnia due to their stimulating effect.
A depressed person may report multiple physical symptoms such as
Appetite often decreases, with resulting weight loss, although increased appetite and weight gain occasionally occur. Family and friends may notice that the person’s behavior is either agitated or lethargic.
The biopsychosocial model proposes that biological, psychological, and social factors all play a role in causing depression.
On the biological side, the monoamine hypothesis is still the predominant biological explanation of depression. The monoamines are serotonine, norepinephrine, and dopamine. The antidepressants act on the neurotransmitter levels or on the receptors.
Serotonin is hypothesized to regulate other neurotransmitter systems; decreased serotonin activity may allow these systems to act in unusual and erratic ways. According to this “permissive hypothesis”, depression arises when low serotonin levels promote low levels of norepinephrine, another monoamine neurotransmitter. Some antidepressants enhance the levels of norepinephrine directly, whereas others raise the levels of dopamine, a third monoamine neurotransmitter. These observations gave rise to the monoamine hypothesis of depression. In its contemporary formulation, the monoamine hypothesis postulates that a deficiency of certain neurotransmitters is responsible for the corresponding features of depression.
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 “Depression”. NIMH. May 2016.
 American Psychiatric Association (2013), Diagnostic and Statistical Manual of Mental Disorders (5th ed.), Arlington: American Psychiatric Publishing, pp. 160–168, ISBN 978-0-89042-555-8
 Global Burden of Disease Study 2013, Collaborators (22 August 2015). “Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013.”. Lancet (London, England). 386 (9995): 743–800. doi:10.1016/S0140-6736(15)60692-4. PMID 26063472.
 Kessler, RC; Bromet, EJ (2013). “The epidemiology of depression across cultures.”. Annual review of public health. 34: 119–38. doi:10.1146/annurev-publhealth-031912-114409. PMC 4100461. PMID 23514317.
 American Psychiatric Association 2000a, p. 349
 American Psychiatric Association 2000a, p. 412
© 2012, 2016 Dr Christian Jonathan Haverkampf. All rights reserved.
Psychotherapy & Counselling, Communication, Medicine (Psychiatry); Dublin, Ireland
This article is solely a basis for academic discussion and no medical advice can be given in this article, nor should anything herein be construed as advice. Always consult a professional if you believe you might suffer from a physical or mental health condition.
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