Causal Pathways to Substance use and Dependence in Young People

Substance use ? tobacco, alcohol and cannabis - and dependence among young people in the UK is widespread. Among young people aged 16-19 over one in four will smoke tobacco; nearly two in five will drink hazardously; one in ten will be regular cannabis smokers. Adolescent substance use is associated with poor educational achievement and antisocial behaviour; psychological problems in early adulthood; and may lead to persistent heavy drinking and smoking in adulthood and the subsequent substantial health related problems. There is no single cause of adolescent substance use. Potential risks include maternal substance use during pregnancy and childhood, family deprivation, and psychological and behavioural problems in early childhood. More evidence is required to tease out the potential contribution of these multiple factors in order to support current and future prevention strategies. This will require detailed information on early life, before substance use, as well as information on how substance use develops during adolescence. Patterns of substance use also have been defined in a variety of ways without a clear definition emerging to date. The ALSPAC cohort, recruited 1991-2, provides the best opportunity to contribute to our understanding of the different trajectories of substance use in adolescents in the UK, on what are the most likely causal pathways leading to substance use and dependence in young people, and on the impact of substance use on adverse adolescent outcomes. Firstly, we will estimate the prevalence of substance use and dependence (separately for tobacco, cannabis and alcohol, and for a combined measure) at age 17-18. We will then identify different trajectories of substance use. Secondly, we will use these substance use trajectories in analyses to test what causal pathways are the most likely. That is, we will test whether a series of factors contribute directly or indirectly (through their impact on other factors) to pattenrs of adolescent substance use, including the influence of maternal substance use whilst pregnant, ADHD and conduct disorder in childhood, parental substance use, deprivation, age starting drug use, and genes associated with cannabis metabolism.
Thirdly, we will examine the impact of different substance use trajectories on adverse adolescent outcomes (poor educational performance, antisocial behaviour, substance dependence, and other drug use). We will test the extent to which substance use has a direct or indirect causal link to these outcomes. Finally, we will provide information for future genetic research and for development of effective interventions.

Substance use, misuse and dependence among adolescents and young people in the UK is among the highest in Europe. Among young people aged 16-19 over one in four will be weekly/daily smokers; nearly two in five will drink hazardously; one in ten will be regular cannabis smokers; and approximately 14% and 8% will be dependent on alcohol and cannabis. Adolescent substance use is associated with poor educational achievement and antisocial behaviour in childhood; adverse psychological problems in early and late adulthood; and adverse trajectories of adult substance use and dependence. More evidence is required to clarify the causal pathways governing the risk of substance use and to tease out the potential contribution of the multiple factors in order to support current and future public health polices and prevention strategies. Patterns of substance use have been defined in a variety of ways without a clear definition emerging. The ALSPAC cohort, recruited 1991-2, provides the best opportunity to contribute to our understanding of the different trajectories of substance use in adolescents in the UK, on what are the most likely causal pathways leading to substance use and dependence in young people, and on the impact of substance use on adverse adolescent outcomes. Firstly, we will estimate the prevalence of substance use and dependence (separately for tobacco, cannabis and alcohol, and a combined measure) at age 17-18 in at least 6000 people. We will use multilevel and latent variable models to examine and identify different trajectories/ phenotypes of substance use. Secondly, we will use these substance use trajectories as outcomes in analyses to test what causal pathways are most consistent with the data. In order to assess whether different factors have a direct or indirect influence on adolescent substance use, including foetal exposure to substance use, ADHD and conduct disorder, parental substance use, social position, age of onset, and functional polymorphisms associated with cannabis metabolism. Thirdly, we will examine the impact of different substance use trajectories on adverse adolescent outcomes (poor educational performance, antisocial behaviour, substance dependence, and other drug use). We will test the extent to which substance use has a direct causal link to these outcomes. Finally, we will provide phenotypic information for future research including studies of alcohol and tobacco specific genes and genome wide association; and qualitative studies of young peoples? perception of different drugs to inform peer-based interventions that can address cannabis and its association with tobacco consumption.