Power et al. (2021) conducted a systematic review and meta-analysis examining how frequent or dependent cannabis use during youth affects Intelligence Quotient (IQ) over time. Their findings provide valuable insights into the potential developmental consequences of cannabis exposure during critical cognitive development periods.
Background
The study focuses on cannabis use among young individuals, a topic of growing concern as cannabis legalization expands worldwide. Previous research has explored the short-term cognitive effects of cannabis, but long-term impacts on intelligence and cognitive development remain less understood. This systematic review and meta-analysis address this gap by evaluating longitudinal data from cohort studies.
Key Insights
- Study Scope: The authors analyzed data from seven cohort studies, covering 808 cannabis users and 5,308 controls. These studies measured IQ both before and after cannabis exposure, providing robust longitudinal evidence.
- Effect on IQ: Frequent or dependent cannabis use was associated with a measurable decline in IQ. The average decline was approximately 2 IQ points, with a Cohen’s d of -0.132 (95% CI -0.198 to -0.066, p < 0.001).
- Quality of Evidence: The included studies were of moderate to high quality, and the results showed low statistical heterogeneity (I2 = 0.2%), suggesting consistent findings across studies.
Significance
The findings highlight the potential long-term cognitive consequences of cannabis use during adolescence, a critical period for brain development. The study emphasizes the importance of considering these effects in public health policies and education campaigns. While the observed IQ decline may appear modest, even small changes can have meaningful implications for academic and professional outcomes over a lifetime.
Future Directions
Power et al. recommend longer follow-up periods in future studies to better understand the developmental impact of cannabis use over time. Further research should also explore how factors such as genetic predisposition, environmental influences, and usage patterns contribute to the observed outcomes.
Conclusion
This meta-analysis provides strong evidence that frequent or dependent cannabis use during youth is associated with IQ decline. The findings underscore the importance of early interventions and public awareness to mitigate the potential negative effects of cannabis on cognitive development.
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
