18.8 million people affected in U.S. in 1998. Affects 1 in 33 children, 1 in 8 adolescents. Lifetime prevalence in US 12% in women, 5% in men. Death from suicide far more common in men. Incidence of postpartum depression up to 10%.

Profound sustained alteration in mood (depression or irritability) for at least 2 weeks, accompanied by 5 of the following: diminished interest or pleasure in almost all activities; weight loss without diet (5% or more of body weight); change in sleep pattern (insomnia or hypersomnia); psychomotor agitation or retardation; fatigue or loss of energy; continuous feelings of worthlessness or excessive or inappropriate guilt; diminished capacity for concentration or indecisiveness; recurrent thoughts of death, recurrent suicidal ideas, attempts, or plans.

Depressive episode precipitated by underlying medical condition, without underlying MDD: may be indistinguishable.

Depressive episode in bipolar disorder (bipolar depression): earlier onset, greater risk of suicide, positive family history, more frequent episodes of illness, prior manic episodes.

Milder forms of depression (fewer than required criteria for MDD): dysthymic disorders, adjustment disorders with depression, depressive personality disorders, seasonal affective disorders, chronic depression, masked depression, atypical depression.

Unknown. Serotonin, norepinephrine implicated.

Most effective initial treatment: combined pharmacotherapy, psychotherapy. Overall response rate near 80%. No proven superiority in effectiveness for any antidepressants (Table 159.1). Selective serotonin inhibitors (SSRIs) more tolerable than tricyclic antidepressants (TCAs). Individual response to given drug unpredictable, though family history of beneficial drug-response or previous response to medication may guide selection. Dose sensitivity varies up to 30-fold. Full benefit may take several weeks.