States that legalized recreational cannabis saw a 15% increase in fatal car crashes
Recreational cannabis legalization in US states was associated with a 15% increase in fatal motor vehicle collisions and a 16% increase in associated deaths, with no conclusive difference between the first year and later years.
Quick Facts
What This Study Found
After adjusting for calendar year, legalization was associated with increased rates of fatal collisions (IRR 1.15, 95% CI 1.06-1.26) and associated deaths (IRR 1.16, 95% CI 1.06-1.27). The difference between the first 12 months post-legalization and subsequent months was inconclusive.
Key Numbers
Fatal collision IRR: 1.15 (95% CI 1.06-1.26). Death IRR: 1.16 (95% CI 1.06-1.27). Data period: 2007-2018. First 12 months vs. later: IRR 0.92 for collisions and deaths (not significant).
How They Did This
Ecologic study using the US Fatality Analysis Reporting System (2007-2018). Examined jurisdiction-specific fatal collision rates before and after legalization using Poisson regression, then meta-analyzed across jurisdictions using DerSimonian and Laird random-effects models.
Why This Research Matters
This multi-state analysis provides population-level evidence of increased traffic fatalities associated with cannabis legalization, informing ongoing policy debates about legalization and road safety.
The Bigger Picture
While the 15% relative increase is statistically significant, it raises important questions about whether improved enforcement, public education, or impaired driving detection could mitigate these effects.
What This Study Doesn't Tell Us
Ecologic design cannot link individual cannabis use to specific crashes. Cannot control for all confounding factors that changed alongside legalization. US Fatality Analysis Reporting System may have reporting variations across jurisdictions.
Questions This Raises
- ?Are the increased fatalities directly caused by cannabis-impaired driving, or do other behavioral changes accompanying legalization play a role?
- ?Would improved impairment detection reduce this effect?
Trust & Context
- Key Stat:
- 15% increase in fatal motor vehicle collisions after cannabis legalization
- Evidence Grade:
- Multi-state analysis with meta-analytic approach, but ecologic design limits causal inference.
- Study Age:
- Published in 2021 using US data from 2007-2018.
- Original Title:
- Association between legalization of recreational cannabis and fatal motor vehicle collisions in the United States: an ecologic study.
- Published In:
- CMAJ open, 9(1), E233-E241 (2021)
- Authors:
- Windle, Sarah B(4), Eisenberg, Mark J(4), Reynier, Pauline, Cabaussel, Josselin, Thombs, Brett D, Grad, Roland, Ells, Carolyn, Sequeira, Crystal, Filion, Kristian B
- Database ID:
- RTHC-03617
Evidence Hierarchy
Watches what happens naturally without intervening.
What do these levels mean? →Frequently Asked Questions
Did fatal car crashes increase after cannabis legalization?
Yes. States that legalized recreational cannabis saw a 15% relative increase in fatal motor vehicle collisions and a 16% increase in associated deaths compared to pre-legalization rates.
Did the increase get worse over time?
No conclusive difference was found between the first year after legalization and subsequent years, suggesting the increase was relatively stable.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-03617APA
Windle, Sarah B; Eisenberg, Mark J; Reynier, Pauline; Cabaussel, Josselin; Thombs, Brett D; Grad, Roland; Ells, Carolyn; Sequeira, Crystal; Filion, Kristian B. (2021). Association between legalization of recreational cannabis and fatal motor vehicle collisions in the United States: an ecologic study.. CMAJ open, 9(1), E233-E241. https://doi.org/10.9778/cmajo.20200155
MLA
Windle, Sarah B, et al. "Association between legalization of recreational cannabis and fatal motor vehicle collisions in the United States: an ecologic study.." CMAJ open, 2021. https://doi.org/10.9778/cmajo.20200155
RethinkTHC
RethinkTHC Research Database. "Association between legalization of recreational cannabis an..." RTHC-03617. Retrieved from https://rethinkthc.com/research/windle-2021-association-between-legalization-of
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.