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Association between legalization of recreational cannabis and fatal motor vehicle collisions in the United States: an ecologic study

Sarah B. Windle, Mark J. Eisenberg, Pauline Reynier, Josselin Cabaussel, Brett D. Thombs, Roland Grad, Carolyn Ells, Crystal Sequeira and Kristian B. Filion
March 17, 2021 9 (1) E233-E241; DOI: https://doi.org/10.9778/cmajo.20200155
Sarah B. Windle
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Mark J. Eisenberg
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Pauline Reynier
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Josselin Cabaussel
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Brett D. Thombs
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Roland Grad
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Carolyn Ells
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Crystal Sequeira
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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Kristian B. Filion
Lady Davis Institute (Windle, Eisenberg, Reynier, Cabaussel, Thombs, Grad, Ells, Sequeira, Filion) and Division of Cardiology (Eisenberg), Jewish General Hospital; Departments of Epidemiology, Biostatistics and Occupational Health (Windle, Eisenberg, Thombs, Filion), Medicine (Eisenberg, Thombs, Filion), Psychiatry (Thombs), Psychology (Thombs), Educational and Counselling Psychology (Thombs), Family Medicine (Grad, Ells) and Social Studies of Medicine (Ells), McGill University; Biomedical Ethics Unit (Ells), Division of Experimental Medicine, McGill University, Montréal, Que.
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  • Figure 1:
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    Figure 1:

    Forest plot of fatal motor vehicle collisions (A) and associated deaths (B) from 2007 to 2018 in United States jurisdictions with legalized recreational cannabis. *Adjusted for calendar year, modelled as a continuous variable. Note: CI = confidence interval, IRR = incidence rate ratio.

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    Figure 2:

    Forest plot of fatal motor vehicle collisions (A) and associated deaths (B) from 2007 to 2018 in United States jurisdictions with open recreational cannabis dispensaries. *Adjusted for calendar year, modelled as a continuous variable. Note: CI = confidence interval, IRR = incidence rate ratio.

Tables

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    Table 1:

    United States jurisdictions with regulations for legalized recreational cannabis in effect before 2019

    JurisdictionDate legalization in effectFirst month legalization in effect for primary analysis*Date commercial dispensaries openFirst month commercial dispensaries open for sensitivity analysis*Cannabis-specific impaired driving law6
    Alaska7,8Feb. 24, 2015March 2015Oct. 29, 2016November 2016None
    California9,10Nov. 9, 2016November 2016Jan. 1, 2018January 2018None
    Colorado11,12Dec. 10, 2012December 2012Jan. 1, 2014January 2014Reasonable inference for impairment ≥ 5 ng/mL THC†
    District of Columbia13Feb. 26, 2015March 2015No commercialNANone
    Maine14,15Jan. 30, 2017February 2017Oct. 9, 2020NANone
    Massachusetts16,17Dec. 15, 2016December 2016Nov. 20, 2018December 2018None
    Michigan18–20Dec. 6, 2018December 2018Dec. 1, 2019‡NAZero tolerance (no detectable presence of cannabis permitted)
    Nevada21,22Jan. 1, 2017January 2017July 1, 2017July 2017Per se limit ≥ 2 ng/mL THC§
    Oregon23–25July 1, 2015July 2015Oct. 1, 2015¶October 2015None
    Vermont26July 1, 2018July 2018No commercial dispensariesNANone
    Washington27,28Dec. 6, 2012December 2012July 8, 2014July 2014Per se limit ≥ 5 ng/mL THC§
    • Note: NA = no data available for legalized (or commercial dispensaries open) months before 2019, THC = tetrahydrocannabinol.

    • ↵* Rounded up or down to the nearest full month of legalization (or commercial dispensaries opening, for sensitivity analysis).

    • ↵† Reasonable inference requires that the jurisdiction must prove with other evidence, in addition to exceeding the legal THC limit, that the driver was impaired.

    • ↵‡ On Dec. 1, 2019, existing medical cannabis dispensaries in Michigan were permitted to transfer up to 50% of their medical cannabis inventory to recreational cannabis inventory. Until November 2021, retailers must hold a medical cannabis licence in order to apply for a recreational cannabis licence.

    • ↵§ Per se limits do not require that the jurisdiction prove that drivers were impaired in order to charge them with driving under the influence if their THC level exceeded the legal limit.

    • ↵¶ On Oct. 1, 2015, existing medical cannabis dispensaries in Oregon were permitted to sell recreational cannabis. The first licences were issued to recreational cannabis retailers on Oct. 1, 2016.

    • View popup
    Table 2:

    Fatal motor vehicle collisions and associated deaths from 2007 to 2018 in United States jurisdictions with legalized recreational cannabis

    EventNo. of eventsPerson-years of observationRate per 100 000 person-years (95% CI)IRR (95% CI)
    CrudeAdjusted*
    Recreational cannabis legalization (11 jurisdictions)†‡
    Fatal motor vehicle collision73 982924 545 8138.00 (7.94–8.06)
     No legalization56 866717 561 813.47.92 (7.86–7.99)1.00 (reference)1.00 (reference)
     Legalization17 116206 983 999.68.27 (8.15–8.39)1.05 (0.99–1.12)1.15 (1.06–1.26)
    Death from motor vehicle collision80 402924 545 8138.70 (8.64–8.76)
     No legalization61 822717 561 813.48.62 (8.55–8.68)1.00 (reference)1.00 (reference)
     Legalization18 580206 983 999.68.98 (8.85–9.11)1.04 (0.98–1.11)1.16 (1.06–1.27)
    Opening of recreational cannabis dispensaries (7 jurisdictions)†§
    Fatal motor vehicle collision60 518774 128 5987.82 (7.76–7.88)
     No open dispensaries50 275653 841 729.27.69 (7.62–7.76)1.00 (reference)1.00 (reference)
     Open dispensaries10 243120 286 868.88.52 (8.35–8.68)1.08 (1.03–1.14)1.18 (1.06–1.32)
    Death from motor vehicle collision65 835774 128 5988.50 (8.44–8.57)
     No open dispensaries54 685653 841 729.28.36 (8.29–8.43)1.00 (reference)1.00 (reference)
     Open dispensaries11 150120 286 868.89.27 (9.10–9.44)1.08 (1.03–1.14)1.18 (1.06–1.32)
    • Note: CI = confidence interval, IRR = incidence rate ratio.

    • ↵* Adjusted for calendar year, modelled as a continuous variable.

    • ↵† See Appendix 1, Supplemental Tables S1–S4 (available at www.cmajopen.ca/content/9/1/E233/suppl/DC1) for jurisdiction-specific event rates.

    • ↵‡ The variance inflation factor for calendar year and legalization status ranged from 1.02 in Michigan to 4.03 in Colorado and Washington (Appendix 1, Supplemental Table S5).

    • ↵§ The variance inflation factor for calendar year and open dispensary status ranged from 1.02 in Michigan to 3.76 in Colorado (Appendix 1, Supplemental Table S5).

    • View popup
    Table 3:

    Fatal motor vehicle collisions and associated deaths from 2007 to 2018 in United States jurisdictions with legalized recreational cannabis, comparing the first 12 months to subsequent months

    EventNo. of eventsPerson-years of observationRate per 100 000 person-years (95% CI)IRR (95% CI)
    CrudeAdjusted*
    Recreational cannabis legalization
    Fatal motor vehicle collision73 982924 545 8138.00 (7.94–8.06)
     No legalization68 180855 020 030.87.92 (7.86–7.99)1.00 (reference)1.00 (reference)
     First 12 mo after legalization†580269 525 782.38.35 (8.13–8.56)1.01 (0.93–1.11)1.12 (1.01–1.23)
     Subsequent months after legalization‡11 314137 458 217.38.23 (8.08–8.38)1.06 (1.00–1.13)1.22 (1.11–1.35)
     First 12 mo v. subsequent months‡–––0.96 (0.88–1.05)0.92 (0.84–1.02)
    Death from motor vehicle collision80 402924 545 8138.70 (8.64–8.76)–
     No legalization61 822717 561 813.48.62 (8.55–8.68)1.00 (reference)1.00 (reference)
     First 12 mo after legalization†629069 525 782.39.05 (8.83–9.27)1.00 (0.92–1.10)1.11 (1.00–1.24)
     Subsequent months after legalization‡12 290137 458 217.38.94 (8.78–9.10)1.06 (1.00–1.12)1.23 (1.11–1.37)
     First 12 mo v. subsequent months‡–––0.96 (0.89–1.04)0.92 (0.84–1.01)
    Opening of recreational cannabis dispensaries
    Fatal motor vehicle collision60 518774 128 5987.82 (7.76–7.88)
     No open dispensaries50 275653 841 729.27.69 (7.62–7.76)1.00 (reference)1.00 (reference)
     First 12 mo of open dispensaries†496860 437 733.98.22 (7.99–8.45)1.03 (0.95–1.13)1.13 (1.03–1.24)
     Subsequent months of open dispensaries‡527559 849 134.98.81 (8.58–9.05)1.13 (1.08–1.18)1.34 (1.24–1.46)
     First 12 mo v. subsequent months‡–––0.92 (0.82–1.04)0.88 (0.76–1.02)
    Death from motor vehicle collision65 835774 128 5988.50 (8.44–8.57)
     No open dispensaries54 685653 841 729.28.36 (8.29–8.43)1.00 (reference)1.00 (reference)
     First 12 mo of open dispensaries†542660 437 733.98.98 (8.74–9.22)1.03 (0.95–1.13)1.13 (1.03–1.25)
     Subsequent months of open dispensaries§572459 849 134.99.56 (9.32–9.82)1.12 (1.07–1.17)1.35 (1.25–1.45)
     First 12 mo v. subsequent months§–––0.92 (0.82–1.03)0.88 (0.76–1.01)
    • Note: CI = confidence interval, IRR = incidence rate ratio.

    • ↵* Adjusted for calendar year, modelled as a continuous variable.

    • ↵† Includes up to 12 months for each jurisdiction (some jurisdictions contributed less than 12 mo, depending on their dates of legalization or opening of dispensaries).

    • ↵‡ Excludes Michigan and Vermont (no subsequent months of legalization available).

    • ↵§ Excludes California and Massachusetts (no subsequent months of open dispensaries available).

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Association between legalization of recreational cannabis and fatal motor vehicle collisions in the United States: an ecologic study
Sarah B. Windle, Mark J. Eisenberg, Pauline Reynier, Josselin Cabaussel, Brett D. Thombs, Roland Grad, Carolyn Ells, Crystal Sequeira, Kristian B. Filion
Jan 2021, 9 (1) E233-E241; DOI: 10.9778/cmajo.20200155

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Association between legalization of recreational cannabis and fatal motor vehicle collisions in the United States: an ecologic study
Sarah B. Windle, Mark J. Eisenberg, Pauline Reynier, Josselin Cabaussel, Brett D. Thombs, Roland Grad, Carolyn Ells, Crystal Sequeira, Kristian B. Filion
Jan 2021, 9 (1) E233-E241; DOI: 10.9778/cmajo.20200155
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