In a prospective study of over 1800 interviewed young Finnish twins, early-onset depressive disorders at age 14 significantly predicted daily smoking, smokeless tobacco use, frequent illicit drug use, frequent alcohol use and recurrent intoxication three years later, even among those adolescents who were not users at baseline.

Analysis of twins discordant for early-onset depressive disorders confirm predictive associations of early-onset depressive disorders with smokeless tobacco use and frequent drinking at age 17½, in within-family replications with co-twins matched on half or all their segregating genes, and on their family structure, socio-economic status, and household environment.

"The findings of this large population-based study emphasize the importance of early-onset depressive disorders in developmental trajectories of substance use", says researcher Elina Hakola, University of Helsinki, Finland. Analyses that control for shared genetic and familial background factors suggest that influences other than family environments, for example, the influence of peers or dispositional personality traits on health-adversing behaviors in adolescence may also be of importance in this association.

The results have important implications for educational purposes in treatment and prevention programs in adolescent health care.