Aims
To estimate the impact of recreational and medical cannabis laws (RCL, MCL) on the use of cannabis and cigarettes in the United States.
Design
A difference‐in‐difference approach was applied to data from the 2004–17 National Survey on Drug Use and Health (NSDUH).
Setting
United States.
Participants
Nationally representative cross‐sectional survey of Americans aged 12 years and older (combined analytical sample for 2004–17, n = 783 663).
Measurements
Data on past‐month use of (1) cigarettes and (2) cannabis were used to classify respondents into four groups: cigarette and cannabis co‐use, cigarette‐only use, cannabis‐only use or no cigarette or cannabis use. State of residence was measured by self‐report. MCL/RCL status came from state government websites.
Findings
Difference‐in‐difference analyses suggest that MCL was associated with an increase in cigarette–cannabis co‐use overall [adjusted odds ratio (aOR) = 1.09; 95% confidence interval (CI) = 1.02–1.16], with the greatest increases among those aged 50 years and above (aOR = 1.60; CI = 1.39–1.84), married (aOR = 1.19; CI = 1.07–1.31), non‐Hispanic (NH) black (aOR = 1.14; CI = 1.02–1.07) and with a college degree or above (aOR = 1.15; CI = 1.06–1.24). MCL was associated with increases in cigarette‐only use among those aged 50 years and above (aOR = 1.07; CI = 1.01–1.14) and NH black (aOR = 1.16; CI = 1.06–1.27) and increases in cannabis‐only use among those aged 50 years and above (aOR = 1.24; CI = 1.07–1.44) and widowed/divorced/separated (aOR = 1.18; CI = 1.01–1.37). RCL was associated with an increase in cannabis‐only use overall (aOR = 1.21; 95% CI = 1.09–1.34), a decline in cigarette‐only use overall (aOR = 0.89; 95% CI = 0.81–0.97) and increases in co‐use among those who were married (aOR = 1.24; CI = 1.02–1.50) and aged 50 years and above (aOR = 1.37; CI = 1.03–1.84).
Conclusions
Recreational and medical cannabis legalization have had a varying impact on the use, and co‐use, of cannabis and cigarettes in the United States.