In plain language
Heavy long-term cannabis use is known to impair memory in adults, but adolescents may be even more vulnerable because their brains are still developing. This study asked whether teenage cannabis users already show memory problems after only a few years of use, and whether those problems can be separated from the effects of alcohol. The researchers tested 181 Australian adolescents aged 16-20 using the Rey Auditory Verbal Learning Test, one of the most widely used measures of learning and memory, comparing cannabis users (52 teens averaging 2.4 years of use, about 14 days per month), alcohol users (67) and non-user controls (62). Importantly, the groups were matched for age, education and premorbid intellectual ability — measured prospectively before drug use began — and cannabis and alcohol users were matched on alcohol consumption.
The results were clear: cannabis-using adolescents performed significantly worse than both alcohol users and non-users on every performance index, recalling fewer words overall and showing impaired learning, retention and retrieval, with moderate-to-large effect sizes (Cohen's d 0.43-0.84). The degree of impairment tracked the duration, quantity, frequency and age of onset of cannabis use, but was unrelated to alcohol or other drug use, and remained after controlling for premorbid intellectual ability. Teens who started using regularly at a younger age had worse memory even after accounting for how much cannabis they had used.
Despite relatively brief exposure, these adolescent users showed memory deficits similar to those reported in adult long-term heavy users. The findings indicate that cannabis adversely affects the developing brain and reinforce public health concerns about early-onset use during adolescence.
Key findings
- Adolescent cannabis users (n = 52) performed significantly worse than alcohol users (n = 67) and non-users (n = 62) on all verbal learning and memory indices of the Rey Auditory Verbal Learning Test.
- Cannabis users recalled fewer words overall and showed impaired learning (p < .001), retention (p < .001) and retrieval (p < .05), with effect sizes of Cohen's d 0.43-0.84.
- Memory impairment was dose-related: it worsened with longer duration, greater quantity and frequency, and earlier age of onset of cannabis use.
- Impairment was unrelated to alcohol exposure or other drug use, and the groups were matched on age, education and prospectively assessed premorbid intellectual ability.
- Earlier onset of regular cannabis use predicted worse memory performance even after controlling for total cannabis exposure.
- After an average of only 2.4 years of use, adolescent users showed deficits similar to adult long-term heavy users — evidence that cannabis adversely affects the developing brain.
How to cite
APA
Solowij, N., Jones, K. A., Rozman, M. E., Davis, S. M., Ciarrochi, J., Heaven, P. C. L., Lubman, D. I., & Yücel, M. (2011). Verbal learning and memory in adolescent cannabis users, alcohol users and non-users. Psychopharmacology, 216(1), 131–144. https://doi.org/10.1007/s00213-011-2203-x
BibTeX
@article{solowij2011verbal,
author = {Solowij, Nadia and Jones, Katy A. and Rozman, Megan E. and Davis, Sasha M. and Ciarrochi, Joseph and Heaven, Patrick C. L. and Lubman, Dan I. and Y{\"u}cel, Murat},
title = {Verbal learning and memory in adolescent cannabis users, alcohol users and non-users},
journal = {Psychopharmacology},
year = {2011},
volume = {216},
number = {1},
pages = {131--144},
doi = {10.1007/s00213-011-2203-x}
}
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Author: Joseph Ciarrochi (ORCID 0000-0003-0471-8100). Free copy hosted with permission for scholarly use. Please cite the published version via the DOI above.