Will Teen Cannabis Use Impair Cognitive Development?

The relationship between teen cannabis use and cognitive impairment has been studied frequently. One question has been whether the cognitive impairment is causal or consequential to the cannabis use. A study out of Canada sought to answer that question and find out what effects teen cannabis use has on cognition.

The study was performed by a team of researchers from CHU Sainte-Justine and the University of Montreal. It was published in the American Journal of Psychiatry.

Their findings indicate that teen cannabis use is related to impaired cognition in profound ways. Adolescent cannabis used was associated with impairment of important cognitive functions. These impairments appear to be more significant than those observed for alcohol use by teens.


There is an existing body of evidence that alcohol and cannabis use is linked to lower academic performance as well as impairments in memory, attention, learning and decision-making. “While many studies have reported group differences in cognitive performance between young users and non-users, what had yet to be established was the causal and lasting effects of teen substance use on cognitive development,” said co-author and PhD student at Université de Montréal, Jean-François G. Morin.

Senior author and investigator Dr. Patricia Conrod, from the Department of Psychiatry at Université de Montréal, added that “very few studies are designed to look at this question from a developmental perspective. Our study is unique in that it followed a large sample of high school students from 7th to 10th grade using cognitive and substance-use measures. Using this big-data approach, we were able to model the complex nature of the relationship between these sets of variables.”


The researchers tracked 3,826 Canadian adolescents over a four-year period in order to assess the relationship between cannabis use, alcohol and cognitive development in the children. They broke the teens into three usage groups – abstinent, occasional consumer or high consumer.

The design of their assessment model was developmentally sensitive. It allowed them to look closely at the year-to-year changes in substance use and cognitive development. They studied a number of cognitive domains, including inhibition, memory, working memory and perceptual reasoning.


In order to simultaneously test vulnerability as well as concurrent and lasting effects on each cognitive domain, the team used multi-level regression models in the study. They found that vulnerability to alcohol and cannabis use in the teens was linked to lower overall performance across all cognitive domains.

“However, further increases in cannabis use, but not alcohol consumption, showed additional concurrent and lagged effects on cognitive functions, such as perceptual reasoning, memory recall, working memory and inhibitory control,” Conrod said. “Of particular concern was the finding that cannabis use was associated with lasting effects on a measure of inhibitory control, which is a risk factor for other addictive behaviours, and might explain why early onset cannabis use is a risk factor for other addictions.” Morin added: “Some of these effects are even more pronounced when consumption begins earlier in adolescence.”


As we move rapidly in the direction of legalizing cannabis for both medical and recreational use, this study should inform both policies and our general attitude with relation to our teens. We need to consider ways to protect them from the negative impact of consumption. More investment in drug-prevention programs is one way to do this.

“It will be important to conduct similar analyses with this cohort or similar cohorts as they transition to young adulthood, when alcohol and cannabis use become more severe,” Conrod said. “This might be particularly relevant for alcohol effects: while this study did not detect effects of teen alcohol consumption on cognitive development, the neurotoxic effects may be observable in specific subgroups differentiated based on the level of consumption, gender or age.” Morin added: “We also want to identify if these effects on brain development are related to other difficulties such as poor academic performance, neuroanatomical damage, and the risk of future addiction or mental health disorders.”


It seems that as societies move toward legalized cannabis, we may be ignoring some serious issues. Some of those issues may be creating harm for the very people we’re supposed to protect from harm – our children.

Keep the faith and keep after it!

Related Content –
Cannabis, Pregnancy And Middle Childhood Mental Health
Alcohol Consumption, Aging And Cognitive Function

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Journal Reference – Jean-François G. Morin, Mohammad H. Afzali, Josiane Bourque, Sherry H. Stewart, Jean R. Séguin, Maeve O’Leary-Barrett, Patricia J. Conrod. A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development. American Journal of Psychiatry, 2018; appi.ajp.2018.1 DOI: 10.1176/appi.ajp.2018.18020202

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