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Early-onset depressive disorders predict the use of addictive substances in adolescence: a prospective study of adolescent Finnish twins.

AIMS
To explore the developmental relationships between early-onset depressive disorders and later use of addictive substances.


DESIGN, SETTING AND PARTICIPANTS
A sample of 1545 adolescent twins was drawn from a prospective, longitudinal study of Finnish adolescent twins with baseline assessments at age 14 years and follow-up at age 17.5 years.


MEASUREMENTS
At baseline, DSM-IV diagnoses were assessed with a professionally administered adolescent version of Semi-Structured Assessment for Genetics of Alcoholism (C-SSAGA-A). At follow-up, substance use outcomes were assessed via self-reported questionnaire.


FINDINGS
Early-onset depressive disorders predicted daily smoking [odds ratio (OR) 2.29, 95% confidence interval (CI) 1.49-3.50, P < 0.001], smokeless tobacco use (OR = 2.00, 95% CI 1.32-3.04, P = 0.001), frequent illicit drug use (OR = 4.71, 95% CI 1.95-11.37, P = 0.001), frequent alcohol use (OR = 2.02, 95% CI 1.04-3.92, P = 0.037) and recurrent intoxication (OR = 1.83, 95% CI 1.18-2.85, P = 0.007) 3 years later. ORs remained significant after adjustment for comorbidity and exclusion of baseline users. In within-family analysis of depression-discordant co-twins (analyses that control for shared genetic and familial background factors), early-onset depressive disorders at age 14 predicted significantly frequent use of smokeless tobacco and alcohol at age 17.5.


CONCLUSIONS
Our results suggest important predictive associations between early-onset depressive disorders and addictive substance use, and these associations appear to be independent of shared familial influences.