Changes in cannabis use modes among Canadian youth across recreational cannabis legalization: Data from the COMPASS prospective cohort study

Introduction: Canadian youth consume cannabis in multiple ways, including by smoking, vaping, and eating or drinking. Existing evidence suggests that these behaviours may change after law liberalization, though data regarding youth are scarce. We investigated changes in cannabis modes of use and associated factors across the federal legalization of recreational cannabis use for adults in Canada, among a large sample of underage youth before alternative products were made legally available. Methods: Data were available from 2953 longitudinally linked Canadian high school students who reported on their cannabis use during the 2017/2018 and 2018/2019 school years. We explored whether students maintained a single or multiple cannabis use mode(s), contracted, or expanded the number of modes used. We then used generalized estimating equations to analyse associations of baseline characteristics with use mode trajectory. Results: Expansion of cannabis use modes (42.3%) was more common than maintenance of a single mode (31.3%), maintenance of multiple modes (14.3%), or reduction (12.1%). Students who maintained multiple modes were significantly more likely to have high amounts of weekly spending money (AOR 1.68), to binge drink (AOR 2.25) or vape (AOR 1.99), to use cannabis regularly (AOR 2.67), and to endorse more symptoms of depression (AOR 1.06). School support for quitting tobacco, drug, or alcohol use appeared to have no effect. Conclusions: Multi-modal cannabis use increased among Canadian youth in our sample. Its association with other substance use and depressive symptoms may indicate clustering of additional harms. Screening for this use pattern may assist in identifying high-risk substance use and should be considered in the design of harm reduction programming.