Background: Although cannabis legalization is associated with increases in self-report cannabis use, biological measures of cannabis use are needed to address potential bias introduced by improved self-reporting of cannabis use in states enacting medical cannabis laws (MCL) and recreational cannabis laws (RCL). Objective: Quantify the role of MCL and RCL enactment in cannabis positive urine drug screen (UDS) prevalence among Veterans Health Administration (VHA) emergency department (ED) patients from 2008 to 2019. Design: Staggered-adoption difference-in-difference analysis were used to estimate the role of MCL and RCL in cannabis positive UDS data, fitting adjusted linear binomial regression models to estimate the association between MCL and RCL enactment and prevalence of cannabis positive UDS. Participants: VHA enrolled veterans aged 18-75 years with ≥1 ED visit in a given year from 2008 to 2019. Main Measures: Receipt of ≥1 cannabis positive UDS during an ED visit were analyzed. Key Results: From 2008 to 2019, adjusted cannabis positive UDS prevalences increased from 16.4% to 25.6% in states with no cannabis law, 16.6% to 27.6% in MCL-only enacting states, and 18.2% to 33.8% in RCL-enacting states. MCL-only and MCL/RCL enactment was associated with a 0.8% (95% CI, 0.4-1.0) and 2.9% (95% CI, 2.5-3.3) absolute increase in cannabis positive UDS, respectively. Significant effect sizes were found for MCL and RCL, such that 7.0% and 18.5% of the total increase in cannabis positive UDS prevalence in MCL-only and RCL states could be attributed to MCLs and RCLs. Conclusions: In this study of VHA ED patients, MCL and RCL enactment played a significant role in the overall increases in cannabis positive UDS. The increase in a biological measure of cannabis use reduces concerns that previously documented increases in self-reported cannabis use from surveys are due to changes in patient willingness to report use as it becomes more legal.

Dr Hasin reported support from Syneos Health for an unrelated project. Dr Wall reported grants from the National Institute on Drug Abuse during the conduct of the study and grants from the National Institutes of Health outside the submitted work. Dr Saxon reported grants from the National Institute on Drug Abuse during the conduct of the study; consulting fees from Indivior, travel support from Alkermes, research support from MedicaSafe, and royalties from UpToDate outside the submitted work. No other disclosures were reported.

Supported by the National Institute on Drug Abuse (grants R01DA048860 and K99DA055724), the New York State Psychiatric Institute, and the VA Centers of Excellence in Substance Addiction Treatment and Education.

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The study was approved by Institutional Review Boards at New York State Psychiatric Institute, VHA Puget Sound and VHA New York Harbor Healthcare Systems.

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