Consequences of cannabis legalization on use and health outcomes on the basis of international experiences

Background: Since 2012, cannabis markets for recreational purposes have been legalized in several US states and in Uruguay and Canada. This presentation provides an overview on the effects of legalizing cannabis markets for recreational purposes in these countries. It is based on a systematic review conducted in 2023 in order to answer different questions regarding the effects in terms of health and use indicators as well as youth protection, illegal markets and crime activities.

Methods: We screened more that 7,000 Studies, N=164 were finally included in the review. Overall, we identified 19 different outcomes, 4 of which were related to consumption and 5 to health.

Results: The majority of studies using self-report or objective (e.g., toxicological) data on THC consumption indicate increasing prevalence of use among adults following the legalization of cannabis, especially in studies with longer follow-up periods (>2 years). Among adults using cannabis, use frequency was not impacted by cannabis legalization. Observed increases in cannabis use disorder (CUD) may be primarily driven by increased use, rather than changes in problems among users. Treatment rates for CUD in the US declined during increasing use prevalence but appear to remain unaffected by cannabis law reforms. With few exceptions, the literature suggests that the number of acute intoxications among adults has increased post legalization in the US (less consistent in Canada). The impact of cannabis legalization on cannabis use among youth cannot be determined with certainty. When examining longer follow-up studies legalizing cannabis may not increase cannabis use among youth in the short term (but perhaps in the long term). The number of acute intoxications has increased post legalization in Canada and US states among children and adolescents. There is insufficient evidence to derive general conclusions on the impact of cannabis legalization on psychosis or schizophrenia among adolescents. Finally, the identified studies mostly converge on the fact that the illegal market can be successfully reduced by cannabis legalization, but it requires several years and an attractive, commercial market or a well-designed government sales monopoly.

Conclusions: In Canada, USA, and Uruguay, cannabis use has become more common before legalization and this trend has continued after legalization. Based on the available evidence it appears that cannabis legalization had no clear short-term impact on chronic health problems (psychosis, hyperemesis), especially with strict regulation of legal sales (or supply). There is less certainty for a long-term impact. Regarding the effects on protection of youth additional, accompanying (prevention) measures are necessary.