What is major depressive disorder?

Major depressive disorder is a debilitating form of depression that prevents sufferers from being able to function normally in their daily lives. Also known as clinical depression, major depressive disorder is estimated to occur in between 5% and 8% of the adult population in the United States in a given year.

Major depressive disorder is often characterized by episodes of intense sadness or irritability lasting at least 2 weeks. While some people may have only one episode of major depression in their lifetimes, it is common for these episodes to recur.

Episodes of major depression often consist of various emotional and physical symptoms. Among the physical (somatic) signs of depression include the following:

Changes in sleep patterns — This can mean sleeping excessively, having trouble initially falling asleep, or waking several hours early and being unable to fall back to sleep.
Changes in appetite — While some people with major depression will lose their appetites and subsequently lose weight, others will find that their appetites increase. In both cases, sufferers from major depression often cease to enjoy food.
Loss of energy — People with major depression often are very tired and have low energy levels, even if they sleep excessively.

Many people seek medical help for these somatic symptoms without realizing that they are a sign of underlying depression. More recognizable are the emotional and mental changes that occur as part of major depression. They may include some or all of the following:

Loss of interest in previously engaging activities — Someone who suffers from depression may no longer care about the activities and interests they once enjoyed.
Withdrawal from social situations and relationships.
A very negative, pessimistic outlook; a feeling of hopelessness about the future.
Low self-esteem, feelings of guilt or self-hatred.
Inability to concentrate, lack of focus.
Irritability or agitation.
Thoughts of suicide.

The underlying cause of major depression is not fully understood, but it is thought to involve abnormalities of the brain. In some cases, depression is hereditary, and in other cases it is related to a person’s environment or circumstances. Most of the time, it is probably a combination of these two factors.

An episode of major depression can sometimes be prompted by a stressful or upsetting life event, such as the death of a loved one, a divorce, or the loss of a job. While sadness or stress is to be expected in these situations, being debilitated by these feelings for more than 1 year indicates that the depression has lasted beyond a reasonable period. Although an initial episode of depression might be triggered by a life event, sometimes the same person will later have episodes with no apparent cause.
Major depression is a serious illness and, like any other illness, needs to be treated. Most people with major depression will undergo treatment with an antidepressant medication. These medications target different neurotransmitters in the brain to improve mood. In addition, it is generally recommended that a depressed person begin psychotherapy with a trained therapist. This treatment enables a person to modify negative thought patterns and better understand the environmental origins of their depression.

Reference:

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001941/.

http://www.brown.edu/Courses/BI_278/Other/Clerkship/Didactics/Readings/major%20depression.pdf.

http://www.nami.org/template.cfm?section=depression.