Abstract Background Little is known about whether cannabis legalization impacts cannabis use uptake or has spillover effects on co-use of cannabis and tobacco/nicotine (using both in the past 30 days). We determined associations of cannabis legalization with self-reported (1) current (past 30-day) cannabis use; (2) current (“now”) tobacco/nicotine use (smoking or electronic cigarette use); and (3) current co-use of cannabis and tobacco/nicotine and how prevalence is changing over time. Methods In this longitudinal study, a web-based survey was administered to a nationally representative, population-based panel of US adults in 2017, 2020, and 2021. We used weighted unadjusted binomial logistic GEE models to assess changes...