Juan Esteban Perez, MD

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The problem: Cannabis policy is changing quickly. However, there is a lack of evidence about the effects that policy changes have on use by adolescents and young adults (AYA).

 

Why do this study? Studies suggest that there are risks of cannabis use in the AYA population.  However, the impact that these changes in policy have in this high-risk group remains unknown.

 

The study: This was a metanalysis if studies testing quantitative differences in cannabis use among individuals < 25 years old, published before March 1st, 2018. A total of 41 studies met the inclusion criteria and were selected for review. Studies were further categorized and analyzed depending on the type of policy change (decriminalization, legalization for medical use, or legalization for recreational use). Of these, 13 studies evaluated the effect of decriminalization, while 20 studies investigated the effect of legalization for medical use. There was no increase in cannabis use pre- and post-policy implementation for medical use or decriminalization. However, the 8 studies of legalization for recreational use found a slight increase in AYA cannabis consumption (mean standardized difference 0.03; 95% CI -0.01 to 0.07). (The “mean standardized difference” is a statistic used in meta-analyses of multiple studies that use different outcomes.  It’s calculated as the observed difference divided by the standard deviation (spread) of all of the results.  A higher standardized difference indicates a larger effect, and 0.03 is rather small).

 

Conclusions: Legalization of cannabis for recreational use may lead to a slightly increased consumption in adolescents and young adults, although decriminalization and legalization for medical use does not.

 

What does this study add?  This is the first study that attempts to evaluate the effect of different types of policy changes regarding cannabis use and its effect on adolescents and young adults.  The studies the authors included were very different, so we should be cautious in drawing any conclusions.  But the finding that policies regarding recreational vs. medical use may have different effects on AYA use are intriguing.

 

Funder: None

 

Author Conflicts: None reported

 

Commentary:  This study is a welcome addition to the evidence on social effects of cannabis legalization, in large part because it has both good and bad news for cannabis proponents and opponents.  The finding that legalizing adult use may increase adolescent use isn’t surprising, but the absence of a similar effect of medical legalization should be reassuring.