What is Major Depressive Disorder (MDD)?

While everyone experiences sadness or depression from time to time, major depressive disorder – also known as clinical depression – is defined as a depressed mood or loss of interest or pleasure in almost all activities that persists for at least two weeks and represents a change from previous functioning. Major depressive disorder causes significant distress or severely impacts a person’s social or work life and other daily routines. It can be diagnosed as mild, moderate or severe, and psychotic symptoms – such as delusions or hallucinations – may be present. 

Signs and Symptoms of Major Depressive Disorder

For a diagnosis of major depressive disorder, five or more of the following characteristics must be present during the same two-week period, represent a change from previous functioning, and include at least one of the major symptoms: depressed mood or loss of interest or pleasure.

Symptoms, which must be present nearly every day, include:

• Depressed mood most of the day, nearly every day, as indicated by self-reporting or through observations made by others; in children and adolescents, this can present as irritability
• Markedly diminished interest or pleasure in all, or almost all, activities for most of the day
• Significant weight loss (without dieting) or weight gain or a decrease or increase in appetite
• Insomnia (inability to sleep) or hypersomnia (excessive sleepiness)
• Inner restlessness or tension associated with increased motor movement (psychomotor agitation) or a slowing-down of thought and a reduction of physical movement (psychomotor retardation), observable by others
• Fatigue or loss of energy
• Feelings of worthlessness or excessive or inappropriate guilt (which may be delusional)
• Diminished ability to think, concentrate or make decisions
• Recurrent thoughts of death (not just fear of dying), suicidal thoughts without a specific plan, or a suicide attempt or a specific plan for committing suicide

The symptoms mentioned above must follow the following diagnostic criteria:

• Cause significant distress/impairment in social, occupational or other functional areas
• Not be attributable to physiological effects of a substance or other medical condition
• Not be better explained by schizoaffective disorder, schizophrenia, schizophreniform disorder, delusional disorder, or other specified and unspecified schizophrenia spectrum and other psychotic disorders
• Not be the result of bereavement or another significant tragedy
• Not occur in addition to a manic episode (a mood state characterized by period of at least one week where an elevated, expansive, or unusually irritable mood exists) or hypomanic episode (a distinct period of abnormally and persistently elevated, expansive or irritable mood and abnormally and persistently increased activity or energy, lasting at least four consecutive days and present most of the day, nearly every day)

Major depressive disorder that continues for more than two years is called persistent depressive disorder or dysthymia.