Researchers examined how recreational and medical cannabis laws (RCL, MCL) have affected the use of cannabis and cigarettes in the United States.

• Data from the 2004–17 National Survey on Drug Use and Health (NSDUH) were retrieved for inclusion in difference-in-difference analyses.

• Findings revealed a varying impact of recreational and medical cannabis legalization on the use, and co-use, of cannabis and cigarettes in the United States.

• An increase in cigarette–cannabis co-use was observed overall in correlation with MCL, with the greatest increases among those aged 50 years and above, married, non-Hispanic (NH) black and with a college degree or above.

• There appeared association of MCL with increases in cigarette-only use among those aged 50 years and above and NH black and increases in cannabis-only use among those aged 50 years and above and widowed/divorced/separated.

• Among those who were married and aged 50 years and above, association of RCL was observed with a rise in cannabis-only use overall, a reduction in in cigarette-only use overall and increases in co-use.