Citation

Tefft BC, Arnold LS. Am. J. Epidemiol. 2021; ePub(ePub): ePub.

Copyright

(Copyright © 2021, Oxford University Press)

DOI

10.1093/aje/kwab184

PMID

unavailable

Abstract

Washington State legalized recreational cannabis consumption in December 2012. We used data on all drivers involved in fatal crashes in Washington in years 2008-2019 (n=8,282) to estimate prevalence in fatal crashes of drivers with ∆9-tetrahydrocannabinol (THC, the main psychoactive compound in cannabis) in their blood before and after legalization. However, nearly half of the drivers were not tested for drugs; we used multiple imputation to estimate THC presence and concentration among them. We used logistic regression followed by marginal standardization to estimate the adjusted prevalence of THC-positive drivers after legalization relative to what would have been predicted without legalization. In the combined observed and imputed data, the proportion of drivers positive for THC was 9.3% before and 19.1% after legalization (adjusted Prevalence Ratio: 2.3, 95% Confidence Interval: 1.3, 4.1). The proportion of drivers with high THC concentrations increased substantially (adjusted Prevalence Ratio: 4.7, 95% Confidence Interval: 1.5, 15.1). Some of the increased prevalence of THC-positive drivers might have reflected cannabis use unassociated with driving; however, the increased prevalence of drivers with high THC concentrations suggests increased prevalence of driving shortly after using cannabis. Other jurisdictions should compile quantitative data on drug test results of drivers to enable surveillance and evaluation.

Keywords: Cannabis impaired driving

Language: en

Keywords

Marijuana; Cannabis; Impaired driving; Drugged driving