65% of Norwegian Adolescent Cannabis Users Reported at Least One Harm
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- 65% of adolescent cannabis users reported at least one harm, averaging nearly 5 per user
- Evidence Grade:
- Large nationally representative sample with comprehensive harm measure and adjusted analysis; cross-sectional limitation but strong descriptive data
- Study Age:
- Published 2025
- Original Title:
- The Prevalence and Correlates of Cannabis-Related Harms in a Nationally Representative Sample of Norwegian High School Students.
- Published In:
- The Journal of adolescent health : official publication of the Society for Adolescent Medicine, 76(4), 710-717 (2025)
- Authors:
- Bretteville-Jensen, Anne Line(2), Sznitman, Sharon R(12)
- Database ID:
- RTHC-06116
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
What harms do adolescent cannabis users experience?
In this Norwegian study, 65% of adolescent users reported at least one harm, with feelings of shame (44%), adverse psychoactive effects (42%), relationship damage (21%), and risky sexual behavior (17%) most common.
Does using cannabis more often cause more harm?
Surprisingly, frequency of use alone did not predict more harms. Instead, starting cannabis younger and using it simultaneously with alcohol were the strongest predictors of experiencing more cannabis-related harms.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-06116APA
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
MLA
Bretteville-Jensen, Anne Line, et al. "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, 2025. https://doi.org/10.1016/j.jadohealth.2024.11.249
RethinkTHC
RethinkTHC Research Database. "The Prevalence and Correlates of Cannabis-Related Harms in a..." RTHC-06116. Retrieved from https://rethinkthc.com/research/bretteville-jensen-2025-the-prevalence-and-correlates
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.