Background: Approximately 36% of current cannabis users report vaping cannabis, but studies on cannabis vaping are limited. Past studies on cannabis vaping focused on mono-use of cannabis vaping, despite the likelihood of poly-substance use among its users. Moreover, studies often failed to account for states' recreational cannabis legalization (RCL) status. The purpose of this study was to (1) analyze patterns of cannabis vaping and concurrent use of other substances among U.S. young adults, and (2) compare predictors of poly-substance use by RCL status.

Methods: This study used the restricted data files of the Population Assessment of Tobacco and Health Study (PATH, waves 4-7). Latent class analysis (LCA) was used to identify substances that co-occur with cannabis vaping.

Results: Overall, LCA identified models with four classes (abstainers, drinkers, smoker-drinkers, and poly-substance users) to explain co-occurrence of ten substance groups (cannabis vaping, joint smoking, blunt smoking, alcohol, nicotine smoking, nicotine vaping, cigar, other tobacco product, prescription drugs, and hard drugs). Cannabis use tended to co-occur with other substances regardless of its mode of use. Stratified LCA showed that states with RCL had a relatively smaller proportion of individuals identified as abstainers (γ = 0.48 vs. 0.52), while having a relatively larger proportion of individuals identified as poly-substance users (γ = 0.17 vs. 0.10). However, predictors of polysubstance use did not notably differ by RCL status.

Conclusions: Future substance-use research must account for RCL status. Individuals reporting cannabis use may be most susceptible to poly-substance use.