Population study of 3,826 teenagers found cannabis, more than alcohol, caused lasting cognitive deficits
Adolescent cannabis use showed both immediate and lasting (neurotoxic) effects on inhibitory control, working memory, memory recall, and perceptual reasoning, with effects more pronounced than alcohol and independent of it.
Quick Facts
What This Study Found
Cannabis showed lagged (neurotoxic) effects on inhibitory control and working memory, and concurrent effects on delayed memory recall and perceptual reasoning. These effects were independent of alcohol use. Alcohol showed vulnerability effects but no evidence of lasting (lagged) cognitive impact. Some evidence of developmental sensitivity was found for cannabis effects.
Key Numbers
3,826 students from 31 schools; 4 annual assessments; 4 cognitive domains tested; cannabis showed significant lagged effects on inhibitory control and working memory; cannabis effects independent of alcohol effects.
How They Did This
Population-based longitudinal study of 3,826 seventh-graders from 31 schools in Greater Montreal, assessed annually for 4 years on substance use and four cognitive domains using computerized testing. Multilevel regression models tested vulnerability, concurrent, and lagged effects.
Why This Research Matters
Published in the American Journal of Psychiatry, this study separates four theoretical models of how substances affect cognition and finds that cannabis uniquely shows the neurotoxicity pattern (lasting effects from prior use), while alcohol does not.
The Bigger Picture
This is among the strongest evidence that adolescent cannabis is worse for cognition than adolescent alcohol, a finding that challenges the popular perception of cannabis as the "safer" substance for teenagers.
What This Study Doesn't Tell Us
Self-reported substance use. Cannabis potency not assessed. Four-year follow-up may not capture long-term recovery. Greater Montreal population may not generalize globally. Computerized cognitive testing may miss real-world functional impairment.
Questions This Raises
- ?Do the cognitive effects persist beyond adolescence?
- ?Would the effects be greater with today's higher-potency cannabis?
- ?Can early cognitive effects predict later psychiatric outcomes?
Trust & Context
- Key Stat:
- Cannabis worse than alcohol for cognition
- Evidence Grade:
- Strong: large population-based longitudinal study with annual assessments and sophisticated modeling, published in Am J Psychiatry.
- Study Age:
- Published in 2019.
- Original Title:
- A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development.
- Published In:
- The American journal of psychiatry, 176(2), 98-106 (2019)
- Authors:
- Morin, Jean-François G, Afzali, Mohammad H(2), Bourque, Josiane(2), Stewart, Sherry H, Séguin, Jean R, O'Leary-Barrett, Maeve, Conrod, Patricia J
- Database ID:
- RTHC-02194
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Is cannabis or alcohol worse for teenage brains?
This study found cannabis had lasting (neurotoxic) effects on inhibitory control and working memory that alcohol did not show, suggesting cannabis is more cognitively harmful during adolescence.
Are the cognitive effects permanent?
The study found lagged effects (current cognition affected by past cannabis use), indicating lasting impact within the 4-year study period. Whether effects persist into adulthood was not assessed.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-02194APA
Morin, Jean-François G; Afzali, Mohammad H; Bourque, Josiane; Stewart, Sherry H; Séguin, Jean R; O'Leary-Barrett, Maeve; Conrod, Patricia J. (2019). A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development.. The American journal of psychiatry, 176(2), 98-106. https://doi.org/10.1176/appi.ajp.2018.18020202
MLA
Morin, Jean-François G, et al. "A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development.." The American journal of psychiatry, 2019. https://doi.org/10.1176/appi.ajp.2018.18020202
RethinkTHC
RethinkTHC Research Database. "A Population-Based Analysis of the Relationship Between Subs..." RTHC-02194. Retrieved from https://rethinkthc.com/research/morin-2019-a-populationbased-analysis-of
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.