Major Depression

The onset of the first episode of major depression may not be obvious if it is gradual or mild. The symptoms of major depression characteristically represent a significant change from how a person functioned before the illness. The symptoms of depression include:

  • little interest or pleasure in doing things;
  • feeling down, depressed or hopeless;
  • trouble falling or staying asleep or sleeping too much;
  • feeling tired or having little energy;
  • poor appetite or overeating;
  • feeling bad about yourself, that you are a failure or have let yourself or your family down;
  • trouble concentrating on things, such as reading the newspaper or watching television;
  • moving or speaking so slowly that other people could have noticed or the opposite in that you are so fidgety or restless that you have been moving around a lot more than usual; and
  • thoughts that you would be better off dead or of hurting yourself in some way.
When several of these symptoms of depressive illness occur at the same time, last longer than two weeks and interfere with ordinary functioning, professional treatment is needed.

Causes of Depression

There is no single cause of major depression. Psychological, biological and environmental factors may all contribute to its development. Whatever the specific causes of depression, scientific research has firmly established that major depression is a biological, medical illness.

Norepinephrine, serotonin and dopamine are three neurotransmitters (chemical messengers that transmit electrical signals between brain cells) thought to be involved with major depression. Scientists believe that if there is a chemical imbalance in these neurotransmitters, then clinical states of depression result. Antidepressant medications work by increasing the availability of neurotransmitters or by changing the sensitivity of the receptors for these chemical messengers.

Scientists have also found evidence of a genetic predisposition to major depression. There is an increased risk for developing depression when there is a family history of the illness. Not everyone with a genetic predisposition develops depression, but some people probably have a biological make-up that leaves them particularly vulnerable to developing depression. Life events, such as the death of a loved one, a major loss or change, chronic stress, and alcohol and drug abuse, may trigger episodes of depression. Some illnesses such as heart disease and cancer and some medications may also trigger depressive episodes. It is also important to note that many depressive episodes occur spontaneously and are not triggered by a life crisis, physical illness or other risks.

Diagnosing Depression

The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV) is the current reference used by health care professionals to diagnose mental illnesses such as depression. This manual was first published in 1952 and has since gone through several revisions. The current edition was published in 1994 (The DSM-IV-TR, or text revision, was produced in 2000) and lists over 200 mental health conditions and the criteria required for each one in making an appropriate diagnosis. The next edition of the DSM is scheduled to publish in May 2012.

Diagnostic criteria for depression can be described as descriptions of symptoms that fall into categories: Affective, or mood, symptoms; behavioral symptoms including withdrawal; cognitive symptoms including problems concentrating or making decisions; and somatic or physical symptoms that may include sleep disturbances.

The DSM-IV is not used to categorize people (as 'a person is depressed') but to describe conditions or illnesses that people have ('the person has depression'). It is very useful as a tool and guide for communicating clearly regarding depression and to ensure best treatment decisions based on evidence or research results acquired by health care professionals.

The content of this fact sheet was adapted from material published by the National Institute of Mental Health