The way depression is defined and understood has changed through history as more knowledge has been acquired about the physical and mental changes that occur when a person is depressed. Research has shown that depression physically changes the neurological makeup of the brain. Subsequently, psychiatrists’ thinking about depression has changed from being a “state of mind” to being a treatable illness.

The National Institute of Mental Health definition of depression is:
A depressive disorder is an illness that involves the body, mood and thoughts. It affects the way a person eats and sleeps, the way one feels about oneself, and the way one thinks about things. A depressive disorder is not the same as a passing blue mood. People with a depressive illness cannot merely “pull themselves together” and get better. Without treatment, symptoms can last weeks, months or years. Appropriate treatment, however, can help people who suffer from depression.

Clinical trials and population surveys have linked depression to specific feelings and behaviors. By assessing these feelings and behaviors, structured diagnostic systems such as the DSM-IV (the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders) can accurately diagnose individuals who have mental disorders such as major depression. The DSM-IV criteria for diagnosis of depression are as follows:

1.	At least five of the symptoms described below are present during the same two week period.
2.	These symptoms must represent a change from a previous level of functioning.
Depressed mood, nearly every day during most of the day. Marked diminished interest or pleasure in almost all activities. Significant weight loss (when not dieting), weight gain, or a change in appetite. Insomnia or hypersomnia (excess sleep). Psychomotor agitation or psychomotor retardation. Fatigue or loss of energy. Feelings of worthlessness or inappropriate guilt. Impaired ability to concentrate or indecisiveness. Recurrent thoughts of death, recurrent suicidal.

Diagnosing depression in research

Depression screening recommendations

	Back