A primary mood disorder characterized by a sustained feeling of sadness and/or decreased interest in all or most activities once enjoyed (anhedonia), which represents a change from previous functioning



  • In the United States, 8.1% of adults age ≥20 years experienced depression in a given 2-week period between 2013 and 2016.
  • 19.2% lifetime risk of having major depressive disorder (MDD)


  • Non-Hispanic Asian adults had the lowest prevalence of depression (3.1%) compared with Hispanic (8.2%), non-Hispanic white (7.9%), and non-Hispanic black (9.2%) adults. This pattern was observed among both men and women.
  • Among all race and Hispanic-origin groups (except non-Hispanic Asian), men had a significantly lower prevalence of depression compared with women.
  • Prevalence decreases with increasing levels of family income for both men and women.
  • Predominant age: low risk before early teens but highest prevalence in teens and young adults

Etiology and Pathophysiology

There are diverse theories regarding the pathophysiology; none proven

Multiple gene loci place a person at increased risk when faced with environmental stressor; twin studies suggest 37% concordance.

Risk Factors

  • Female > male (2:1)
  • Severity of first episode
  • Persistent sleep disturbances
  • Presence of chronic disease(s), recent myocardial infarction (MI), cardiovascular accident (CVA)
  • Strong family history (depression, bipolar, suicide, substance abuse), spouse with depression
  • Childhood trauma/maltreatment
  • Substance abuse and dependence, domestic abuse/violence
  • Losses, stressors, unemployment
  • Single, divorced, or unhappily married

Commonly Associated Conditions

  • Bipolar disorder, cyclothymic disorder, grief reaction, anxiety disorders, somatoform disorders, schizophrenia/schizoaffective disorders
  • Medical comorbidity
  • Substance abuse

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