"Clinical depression" - herein referred to as a major depressive episode - is a common, debilitating condition that is estimated to affect approximately 7% of the U.S. population on an annual basis and 17% over the lifespan.[*] The diagnosis of major depressive episode is based upon certain criteria that are defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM).[*] The latest version of the DSM (DSM-IV-TR) defines a major depressive episode as follows:

A. Five (or more) of the following symptoms have been present during the same 2-week period and represent a change from previous functioning; at least one of the symptoms is either:

1. depressed mood or
2. loss of interest or pleasure

Note: Do not include symptoms that are clearly due to a general medical condition, or mood-incongruent delusions or hallucinations.

1. depressed mood most of the day, nearly every day, as indicated by either subjective report (e.g., feels sad or empty) or observation made by others (e.g., appears tearful). Note: In children and adolescents, can be irritable mood.
2. markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day (as indicated by either subjective account or observation made by others)
3. significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or decrease or increase in appetite nearly every day. Note: In children, consider failure to make expected weight gains.
4. insomnia or hypersomnia nearly every day
5. psychomotor agitation or retardation nearly every day (observable by others, not merely subjective feelings of restlessness or being slowed down)
6. fatigue or loss of energy nearly every day
7. feelings of worthlessness or excessive or inappropriate guilt (which may be delusional) nearly every day (not merely self-reproach or guilt about being sick)
8. diminished ability to think or concentrate, or indecisiveness, nearly every day (either by subjective account or as observed by others)
9. recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide

B. The symptoms do not meet criteria for a Mixed Episode

C. The symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.

D. The symptoms are not due to the direct physiological effects of a substance (e.g., a drug of abuse, a medication) or a general medical condition (e.g., hypothyroidism).

E. The symptoms are not better accounted for by Bereavement, i.e., after the loss of a loved one, the symptoms persist for longer than 2 months or are characterized by marked functional impairment, morbid preoccupation with worthlessness, suicidal ideation, psychotic symptoms, or psychomotor retardation.

When an individual experiences multiple major depressive episodes over the course of time, he is considered to have recurrent Major Depressive Disorder.[*] As the name implies, this condition is a recurrent, chronic illness that produces a mood (and, often, an anxiety) disturbance and functional impairment in the individual who suffers from it. Major depressive disorder (whether single episode or recurrent) is felt to be a disease condition of the brain, endocrine system, and immune system at some level[*], even while it is well known to be triggered and propelled by psychological stress[*], among other factors.

A major depressive episode is not the equivalent of normal sadness or down moods that follow from emotional losses or setbacks. Major depressive episodes have the potential to so shake up someone's experience of the world that he would rather be put out of existence than go on. Consequently, major depressive disorder is a significant risk factor for suicidal thinking, suicide attempts and suicide completion.[*]

In the U.S., major depressive disorder is most often treated by psychiatrists, psychologists, various other mental health professionals and primary care physicians.

As a psychiatrist who routinely evaluates and treats mood and anxiety disorders, I believe that it is of utmost importance that individuals with major depressive disorder understand their illness as best as possible. A better understanding provides the proper framework for optimal treatment outcomes.