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

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Abstract
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.

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