Substance use disorders are a substantial health and community problem. Traditional prevention strategies that focus on educating people about the dangers of substance use have been to date unsuccessful. In contrast, reductions in substance use disorders can be achieved by reducing risk factors and increasing general mental health and resiliency in young people. Such interventions typically focus on the pathway to substance use disorders through conduct problems and delinquency with their associated features of social adversity, school failure, and family conflict and breakdown. However, increasing evidence shows that there is a related but diverse pathway to substance misuse associated with internalising problems, that is, anxiety and depression. Given that strong evidence shows the incidence of both internalising and externalising problems can be reduced via developmentally informed tertiary and preventive interventions, these strategies have considerable potential for reducing the incidence of substance use disorders in the community. An attempt was made to present a developmental map of the risk and protective factors that influence the persistence versus transience of internalising disorders and externalising disorders in young people. These switch in and out at various developmental points of the lifespan, and thus, a series of windows of opportunity for intervention can be identified.

To demonstrate useful preventive effects for internalising disorders and externalising disorders on substance use disorders, two logical conditions were proposed. First, it must be shown that interventions can reduce internalising disorders and externalising disorders at a community level. In terms of developmental trajectories of anxiety disorders and the available data on intervention effectiveness, anxiety prevention and early intervention during middle to late childhood holds great promise. Family and school-based programs during early childhood have the potential to lay a foundation of social competence, and recent evidence supports the long-term benefits. Developmentally, the primary to early secondary school years, the age of onset of most anxiety disorders, appears to be an optimum time to provide both universal and indicated prevention and early intervention initiatives. Issues of recruitment become more difficult in the adolescent years but programs for depression have shown similar potential. With regard to externalising disorders, middle childhood appears to be a propitious time for prevention. Programs based on behavioural family intervention models that incorporate individual child as well as contextual interventions (i.e., home, school, community) have shown considerable success in reducing externalising disorders.

The second condition is that reductions in the incidence of internalising disorders and externalising disorders must be shown to have an impact on substance use disorders. This has not been demonstrated as yet due to lack of longitudinal studies that test the interweaving pathways of internalising, externalising and substance use disorders, as well as intervention effects. However, two lines of indirect evidence suggest optimism is warranted. First, available data on developmental pathways of internalising disorders, externalising disorders and substance use disorders indicates that the first two groups of disorders precede substance use disorders in a substantial number of cases and may contribute to the occurrence of substance use disorders through a variety of indirect and shared causal links. Second, it has been shown that promotion of resilience in the primary school years, using similar strategies as are used to reduce internalising disorders, do in fact reduce internalising disorders and substance use disorders in the adolescent years.

Is it worth pursuing a focus on internalising disorders and externalising disorders as a way of reducing the incidence of substance use disorders? At this point the answer seems to be an encouraging but cautious 'yes'. A high priority for research should involve longitudinal studies of the inter-relations of internalising, externalising, and substance use disorders through childhood to early adulthood, with a subset of subjects offered intervention for internalising disorders and externalising disorders to assess their impact on substance use disorders.Top of page