Reference
Power, E., Sabherwal, S., Healy, C., O'Neill, A., Cotter, D., & Cannon, M. (2021). Intelligence quotient decline following frequent or dependent cannabis use in youth: a systematic review and meta-analysis of longitudinal studies. Psychological Medicine, 51(2), 194-200. https://doi.org/10.1017/S0033291720005036
Review
In their recent study, Power et al. (2021) aimed to investigate the relationship between frequent and dependent cannabis use among youth and subsequent decline in Intelligence Quotient (IQ). The authors conducted a systematic review and meta-analysis of cohort studies that included pre- and post-exposure measures of IQ in non-treatment-seeking samples.
The authors searched Embase, PubMed, and PsychInfo databases from their inception until 24 January 2020, and pre-registered their review on PROSPERO (ID no. CRD42019125624). A total of seven cohort studies were identified, including 808 cases and 5308 controls. The studies were of moderate to high quality, and there was a low level of statistical heterogeneity (I2 = 0.2%) among them.
The results indicated a significant effect of frequent or dependent cannabis use in youth on IQ change, with a Cohen's d of -0.132 (95% CI -0.198 to -0.066) and p < 0.001. This translates to an average decline of approximately 2 IQ points following exposure to cannabis in youth. The authors suggest that future studies should include longer follow-up periods to assess the magnitude of developmental impact.
This study is an important addition to the literature on the effects of cannabis use on cognitive functioning and intelligence, particularly in young people. By providing a rigorous, systematic review and meta-analysis, Power et al. (2021) offer valuable insights into the potential negative consequences of frequent or dependent cannabis use on IQ and overall cognitive development.
