Importance: Cannabis use has been shown to modestly increase shortly after legalization of recreational use, but little is known about longer-term changes in cannabis and tobacco use.

Question: Is legalizing cannabis associated with use of cannabis, cigarettes, and electronic nicotine delivery systems (ENDS)?

Findings: In this cohort study using difference-in-differences methods to analyze 171 257 observations from 55 406 participants, legalization was associated with increased cannabis use and ENDS use. There was no association with cigarette use.

Meaning: Cannabis and ENDS use increased after cannabis legalization, but there was no evidence of a halt or reverse in the decline in cigarette use.