Maria Melchior, Laura Pryor and Marie Jauffret-Roustide
Our study, recently published in the IJE, shows that youths who initiate cannabis use before the age of 17 years are 60% less likely to pursue higher education than those who never used cannabis. An original aspect of our study, which was based on data from the longitudinal TEMPO cohort in France, is that we were able to take into account youths’ psychological and school difficulties in childhood and adolescence, as well as their parents’ characteristics.
In recent decades, cannabis use has become frequent among youths growing up in Europe, North America and Australasia. The potential health effects of cannabis use include reductions in memory and concentration. Because the brain is thought to develop until the age of 25, adolescent substance use could have lasting negative effects on executive functions, which can in turn result in school difficulties and low educational achievement.
Our study, conducted among 1103 men and women aged 22–35 years in 2009, contributes to research showing that early cannabis use predicts long-term academic difficulties. A specificity of the TEMPO cohort is that all participants were recruited from among the children of participants of another epidemiological cohort study — GAZEL. In 1991, parents who had participated in the GAZEL study completed a questionnaire on their children’s mental health and academic performance (TEMPO participants were aged 4–16 years at the time); in 1999, both the parents and youths completed questionnaires on mental health, substance use (including cannabis) and academic performance. In 2009, TEMPO study participants were contacted again and asked about whether they had tried cannabis and, if so, at what age, as well as about their educational attainment. Following previous research, and because the mean age of cannabis initiation in France is about 17 years, we considered study participants who used cannabis before the age of 17 to be early initiators. In terms of educational attainment, given high levels of high school completion among youths in France (about 80%), we studied whether participants had a higher education degree.
As youths who initiate cannabis early on and those who do so later or never are very different, it was especially important to render these three groups comparable. Based on information regarding participants’ psychological and school difficulties early on, their parents’ socioeconomic background, mental health and substance use, we calculated propensity scores predicting the likelihood of early cannabis initiation, which were then included in our statistical analyses to fully control for selection and confounding factors.
Our results point to two key findings:
- Early cannabis initiation predicts low educational attainment even when accounting for individual and familial vulnerability factors
- Early cannabis use is more likely to result in low educational attainment in girls than in boys.
The long-term academic consequences of early cannabis initiation are consistent with previous scientific literature and can probably be explained by two mechanisms. First, tetrahydrocannabinol — the active ingredient in cannabis — is known to affect brain structures involved in memory, concentration and motivation (e.g. the cortex, amygdala and hippocampus). Because the brain grows and develops until age 25, substance use during this critical period could durably affect these key structures, as well as neural connectivity. Second, youths who initiate cannabis use early on could see their grades fall and their ability to focus on academic matters decrease, which could result in lower motivation for school and fuel a spiral feeding back to cannabis use. This could partly explain large social inequalities with regard to cannabis misuse that are observed from adolescence onwards.
What are the public health implications of our research? The most important one is that early initiation of cannabis is a bad sign for future educational and health outcomes and should be prevented. To effectively dissuade youths from using cannabis, one strategy is to inform them and their parents of associated short-term risks, such as problems with memory and concentration and psychological side effects, including anxiety attacks or “bad trips”. This could be more efficient than focusing on long-term effects that may not fit with teenagers’ concerns. Another promising strategy involves strengthening youths’ ‘psychosocial skills’, which include self-esteem, the ability to deal with emotions and the capacity to express themselves and to solve conflicts. Intervention studies that have tested programs specifically targeting these skills in children and adolescents show that, in the long-term, recipients are less likely to use substances and to have mental health difficulties. Prevention should therefore start early and focus not solely on cannabis use but on youths’ overall psychosocial wellbeing – our results suggest that the gains should extend beyond health to socioeconomic outcomes.
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Maria Melchior holds a PhD in epidemiology and public health (Harvard University). She is currently Research Director at the French National Institute of Health and Medical Research (INSERM). Her research focuses on social inequalities in mental health, with an emphasis on developmental trajectories from childhood to adulthood and the intergenerational transmission of psychiatric disorders. Most projects have relied on data collected in longitudinal cohort studies of children set up in France (EDEN, ELFE, TEMPO) or other countries (Dunedin study in New Zealand, ELDEQ in Canada). Currently, she’s also coordinating the DEPICT repeated cross-sectional study, which aims to evaluate changes in the perception of tobacco smoking and social disparities in this area, particularly among young people. Maria Melchior received the Research Prize of the European Psychiatric Association (2012) and the Early Career Award of the International Society of Behavioral Medicine (2004). She is the author or co-author of over 100 publications in international peer-reviewed journals.
Laura Pryor has a PhD in Public Health with a specialisation in Health Promotion from the University of Montreal. Currently a postdoctoral fellow in Social Epidemiology at INSERM and UPMC Sorbonne Universities, her research is focused on social inequalities in child mental health and development, using longitudinal cohort data in Denmark and France. She also has an interest in how physical and mental health problems are intertwined, particularly problems related to food and nutrition, such as obesity and food insecurity.
Marie Jauffret-Roustide holds a PhD in Sociology and Social Sciences at Paris XI University. She is currently a Research Fellow at INSERM. She leads sociological and public health studies on drug use practices and social processes of at-risk practices among people who use drugs. She is the co-investigator of the COSINUS cohort in Paris, which evaluates the impact of supervised consumption rooms for injecting drug users. She is the leader of international comparative research on harm reduction policies in Europe, including the analysis of the biomedicalisation of addiction, the history of peer education and community-based approaches, and the social acceptability of supervised consumption rooms.
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