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Objective: This study aims to explore the mechanisms of personality-targeted intervention effects on problematic drinking, internalizing and externalizing symptoms. Method: As part of a cluster-randomized trial, 1,210 high-risk students (mean age 13.7 years) in 19 London high schools (42.6% White, 54% male) were identified using the Substance Use Risk Profile Scale. Intervention school participants were invited to participate in personality-matched interventions by trained school staff. MacKinnon's products of coefficients method was used to compare 3 complementary mechanism hypotheses, namely, whether early changes in (a) alcohol use, (b) internalizing and externalizing symptoms, or (c) personality during the 6 months postintervention accounted for intervention effects over 2 years. Results: Early intervention effects on drinking behaviors during the 6 months postintervention partially accounted for longer term intervention effects on the onset of binge drinking (95% confidence interval [CI] [-.349, -.062]) and drinking problems (95% CI [-.206, -.016]) over 2 years. Intervention effects on anxiety symptoms and conduct problems were partially mediated by early reductions in depressive symptoms (95% CI [-.013, -.001]; 95% CI [-.047, -.001]), and intervention effects on internalizing symptoms were also partially mediated by reductions in anxiety sensitivity (95% CI [-.003, 0]). Conclusions: 2-year intervention effects on problematic drinking were largely accounted for by early changes in drinking behaviors, and were not mediated by changes in mental health symptoms or personality risk factors. Early improvements in mood and anxiety sensitivity partially mediated longer term reductions in mental health problems. [ABSTRACT FROM AUTHOR]

Objective: Only a minority of drug and alcohol users develops a substance use disorder. Previous studies suggest that this differential vulnerability commonly reflects a developmental trajectory characterized by diverse externalizing behaviors. In this study, we examined the relation between child and adolescent externalizing behaviors and adolescent substance use in a prospectively followed Canadian birth cohort, accounting for the temporal sequence of a wide variety of contributing factors. Methods: Two hundred and forty-two adolescents followed since birth (date range: 1996 to 2012) were assessed on externalizing behavior (age 17 months to 16 years), alcohol and cannabis use at age 16, age of alcohol use onset, family history of substance use problems, family functioning (age 11 to 15), sensation seeking (age 16), prenatal substance exposure, socioeconomic status (age 1 to 9), and sex. Results: Age of alcohol use onset was predicted by a family history of substance use problems, externalizing traits from ages 6 to 10 and 11 to 16, sensation seeking at age 16, prenatal alcohol and tobacco exposure and family functioning at ages 11 to 15. High frequencies of alcohol and cannabis use at age 16 were both predicted by externalizing traits from ages 11 to 16, a family history of substance use problems and sensation seeking after controlling for other individual, environmental and familial variables. The association between familial substance use problems and substance use during adolescence was partially mediated by externalizing traits from age 11 to 16. Conclusions: The present findings provide prospective evidence for a developmental risk pathway for adolescent substance use, potentially identifying those who could benefit from early interventions. [ABSTRACT FROM AUTHOR]