Prevalence and forms of cannabis use in legal vs. illegal recreational cannabis markets.
Recreational or non-medical cannabis has been legalized in several US states, and was legalized federally in Canada in October 2018. There is little comparative data on product use across jurisdictions, particularly with respect to the types of cannabis products used, which differentially impact health. Data are from Wave 1 of the International Cannabis Policy Study, collected from Aug 27-Oct 7, 2018. Respondents (n 27,024) aged 16-65 completed an online survey measuring patterns of cannabis use, quantities and routes of administration. Respondents were recruited from Canada (n 9976) and US states that had (n 7362) and had not (n 9686) legalized non-medical cannabis (legal and illegal states, respectively). Prevalence of at least daily, weekly, and monthly cannabis use were significantly higher in US legal states (11.3%, 18.2%, 25.0%, respectively) than US illegal states (7.4%, 11.6%, 16.8%, respectively p<0.001) and Canada (8.9%, 14.1%, 19.0%, respectively p ≤ 0.01). Dried herb was the dominant form of cannabis reported by past 12-month users across all jurisdictions (77.7%-80.8%). Although the amount of dried herb used per year did not differ by jurisdiction (range 210.3-229.4 g), those in US legal states were significantly more likely to use dried herb daily or weekly than were those in illegal states and Canada (p<0.001). Use of cannabis concentrates, vaped oils, edibles, and drinks was more prevalent among US legal states than illegal states and Canada (p ≤ 0.001). Vaping dried herb was more common in both legal and illegal US jurisdictions than in Canada (p<0.05), whereas Canadians were more likely to smoke dried herb with tobacco (p<0.001). The prevalence of cannabis use-and use of products such as cannabis concentrates, edibles and drinks-was higher in US states that had legalized cannabis. Additional longitudinal research is required to determine whether these differences reflect causal effects of legalization or pre-existing secular trends.