A difference-indifference approach to examining the impact of cannabis legalization on disparities in the use of cigarettes and cannabis in the United States, 2004-17

Abstract

__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