The role of drug and alcohol abuse in recent increases in depression in the US.

Previous studies have reported an increase in depression among recent birth cohorts. Concurrent with the increase in rates of depression, there have been increases in rates of drug and alcohol abuse and dependence. This study sought to determine if the recent increase in rates of depression could be attributed to co-morbid alcohol and drug abuse. The data derived from two studies: (1) a sample of relatives of probands with affective disorder; and (2) a community survey of the US population. The piecewise exponential statistical model was applied to evaluate the association of gender, age, period and birth cohort with rates of major depressive disorder (MDD) separately for those with, and without, diagnoses of alcohol or drug abuse. Elevated rates of MDD occurred among those with co-morbid drug and alcohol abuse in both the family and community samples. However, there were also temporal increases in rates of MDD in those with no such co-morbidity. Specifically there were effects of age and gender for both studies; in addition, there was a period effect in the family study and a birth cohort effect in the community sample. The recent increases in depression in the US cannot be accounted for solely by concurrent increases in co-morbid drug and alcohol abuse. Temporal (period and cohort) effects on rates of depression occur in addition to the contribution of co-morbid drug and alcohol abuse or dependence.