Ten-year study on cannabis use by youth reveals distressing results

St. Francis Xavier University psychology professor Dr. Kara Thompson has revealed troubling results from cannabis use by Canadian youth.

According to two new studies that followed patterns of marijuana use across a decade in Canadian youth, those who start using cannabis early and continue to use it often are more likely than their peers to have cooccurring problems, poor health outcomes, and less occupational and educational success in young adulthood.

A team of researchers, led by Dr. Kara Thompson, StFX, and Dr. Bonnie Leadbeater, University of Victoria, looked at data from the Victoria Healthy Youth Survey, which followed a cohort of 662 young people over 10 years. The youth, between the ages of 12 and 18 when the study began in 2003, were interviewed every two years about their substance use, mental health, accomplishments and general well-being. The researchers observed how substance use patterns unfolded over time, and how these patterns were influenced by other factors in adolescence and young adulthood.

“We hear a lot of talk about risks for youth using cannabis, especially with legalization around the corner, but our understanding of patterns of cannabis use among Canadian youth over time and the consequences of use is actually quite limited,” says Leadbeater. “Our hope is that this work sheds light on how young Canadians use cannabis across adolescence and young adulthood, what predicts different patterns of use, and how these patterns contribute to mental health and well-being of young people.”

Two studies, published in the Canadian Journal of Behavioural Science and Prevention Science, found five different patterns of cannabis use. Approximately 30 per cent of the youth were classified as high-risk, meaning they started using cannabis frequently in early adolescence or increased in use across adolescents and were using more than once a week by young adulthood. These risky patterns of use were associated with the poorest health outcomes in young adulthood, including higher levels of substance use disorders, mental health and behaviour problems, as well as lower levels of educational and employment outcomes.

“The young people who follow high-risk cannabis patterns are not only using cannabis. They often begin to use other substances (like alcohol) in adolescence, and they are experiencing other behavioural problems that may contribute to both negative outcomes and the initiation of cannabis,” says Thompson. “An effective public health approach to reducing cannabis for youth will need to acknowledge the contexts and co-occurring problems that accompany risky cannabis use in young people.”

Researchers say that findings from this study will provide results that government and other public health practitioners can use to inform current and future cannabis policies.

This project was one of a handful funded by the Canadian Institutes of Health Research to look at how cannabis legalization would affect certain Canadian populations, including youth.