Importance: In the US, cannabis use has nearly doubled during the past decade, in part because states have implemented recreational cannabis laws (RCLs). However, it is unclear how legalization of adult-use cannabis may affect alcohol consumption.

Question: How do recreational cannabis laws affect alcohol use among adults in the US?

Findings: In this cross-sectional study with a difference-in-differences analysis of 4.2 million adults in all 50 states from 2010 to 2019, recreational cannabis laws were associated with a 0.9 percentage point increase in any alcohol use among the population overall but not in binge or heavy drinking. Results were primarily determined by younger adults (18-24 years) and men.

Meaning: These findings suggest that increased alcohol use may be an unintended consequence of recreational cannabis laws.