Age-related differences in the impact of cannabis use on the brain and cognition: a systematic review

Gorey, Claire M.; Kuhns, Lauren; Smaragdi, Eleni; Kroon, Emese; Cousijn, Janna · 2019 · OpenAlex-citations

DOI: 10.1007/s00406-019-00981-7

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Summary

This systematic review investigates whether age moderates the relationship between cannabis use and cognitive outcomes, specifically comparing adolescents to adults. Motivated by the ongoing legalization of cannabis and conflicting theories regarding adolescent brain vulnerability versus resilience, the authors sought to determine if adolescents experience greater cognitive impairment or enhanced recovery compared to adults. Previous reviews often failed to directly compare age groups or relied on retrospective data, leaving the specific moderating role of age unanswered. The study followed PRISMA guidelines, searching databases including MedLine, Cochrane Library, and PsycInfo for studies published before July 2018. Inclusion criteria required studies to formally test the interaction between age (adolescent vs. adult) and cannabis exposure on cognition. The review included both human studies (adolescents <18, adults >18) and rodent studies (post-natal day 25–42 vs. >43) to allow for controlled experimental conditions regarding exposure and abstinence. After screening 2,124 records, 21 studies (15 rodent, 6 human) were included. Human studies were rated for causality strength, while rodent studies were assumed to have strong causal inference due to experimental control. The findings indicate that age-related differences are not uniform but depend on usage patterns and specific cognitive domains. In human studies, general executive functioning appeared more impaired in adolescent frequent cannabis users compared to adult frequent users. Specifically, adolescents with cannabis use disorders showed less improvement in impulsive responding to cannabis cues after treatment compared to adults. Furthermore, age effects were most prominent among heavy or dependent users; for instance, individuals with persistent cannabis dependence diagnosed before age 18 experienced a greater decline in IQ than those diagnosed after 18. However, these vulnerabilities did not persist after sustained abstinence in some contexts, suggesting potential resilience. Rodent studies supported the notion that adolescents may exhibit heightened sensitivity to cannabis-induced deficits in learning and memory, though these effects often resolved after abstinence. The significance of this review lies in its novel approach of directly comparing age groups and integrating animal models to address confounds in human research. The results suggest that while adolescents may be more vulnerable to cognitive impairments during active, heavy use, they may also possess resilience mechanisms that allow for recovery after abstinence. These findings imply that prevention and policy efforts should focus on heavy use patterns in adolescence, as the risks are most acute in this subgroup. The review generates new hypotheses for future research, particularly regarding the transient nature of adolescent cognitive deficits and the specific neural mechanisms underlying age-related differences in cannabis response.

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• cannabis