Among Norwegian adolescents who used cannabis, 65% experienced at least one of 18 measured harms, averaging nearly 5 harms each, with early initiation and combined alcohol-cannabis use as the strongest predictors.
Youth prevention researchers, school counselors, parents, public health officials
65% of adolescent cannabis users reported at least one harm, averaging nearly 5 per user
What the researchers found
65% of adolescent cannabis users reported at least one harm (mean 4.7 harms). The most common were feelings of shame (44%), adverse psychoactive effects (42%), harmed relationships (21%), unprotected/unwanted sex (17%), and school troubles (17%). Early initiation and simultaneous use with alcohol predicted more harms, but frequency of use alone did not.
Why it matters
Most cannabis harm research focuses on clinical disorders or brain effects. This study captures a much wider range of real-world consequences that adolescents actually experience, from shame and relationship damage to sexual risk and academic problems, painting a more complete picture of how cannabis affects young lives.
The numbers in context
3,490 students; 20% lifetime cannabis use; 65% of users reported at least one harm; mean 4.7 harms per user; shame 44%, adverse psychoactive effects 42%, harmed relationships 21%, unprotected/unwanted sex 17%, school troubles 17%; early initiation IRR 1.564 (p < .01); simultaneous alcohol use IRR 1.385 (p < .01); frequency not significant
How the study worked
Nationally representative survey of 3,490 Norwegian high school students (ages 17-19, 48% male). Among the 20% who reported lifetime cannabis use, researchers assessed 18 possible cannabis-related harms and their associations with use patterns, controlling for sociodemographic and temperamental factors.
What this study cannot tell us
Cross-sectional design cannot determine temporal sequence, Norwegian legal context (cannabis illegal) may influence reporting, self-reported harms may be under- or over-reported, 20% lifetime use rate may not generalize to all countries, retrospective recall of harms
How to read the evidence
Large nationally representative sample with comprehensive harm measure and adjusted analysis; cross-sectional limitation but strong descriptive data
When this study was published
Published 2025
The bigger picture
The finding that frequency of use did not predict harm, while early initiation and alcohol co-use did, challenges the intuitive assumption that using more equals more harm. Prevention efforts targeting when and how young people first use cannabis, and discouraging combined alcohol-cannabis use, may be more effective than focusing solely on use frequency.
Questions still open
- Why does frequency of use not predict harm while early initiation does? Would the harm profile look different in countries where cannabis is legal? Do the 35% who reported no harms differ in protective factors beyond initiation age?
Common questions
What harms do adolescent cannabis users experience?
Does using cannabis more often cause more harm?
Read the original research
The Prevalence and Correlates of Cannabis-Related Harms in a Nationally Representative Sample of Norwegian High School Students.
The Journal of adolescent health : official publication of the Society for Adolescent Medicine, 76(4), 710-717
Citation
Bretteville-Jensen, Anne Line; Sznitman, Sharon R. (2025). The Prevalence and Correlates of Cannabis-Related Harms in a Nationally Representative Sample of Norwegian High School Students.. The Journal of adolescent health : official publication of the Society for Adolescent Medicine, 76(4), 710-717. https://doi.org/10.1016/j.jadohealth.2024.11.249
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