Cannabis users in states with recreational or medical legalization reported lower rates of driving under the influence of cannabis compared to users in states without legal cannabis.
Policymakers, traffic safety researchers, and anyone interested in legalization's effects on driving.
59% lower risk of driving high in recreational cannabis states
What the researchers found
Among 1,249 past-30-day cannabis users, the risk of driving within 3 hours of getting high was 59% lower in recreational states (RR 0.41) and 61% lower in medical-only states (RR 0.39) compared to states without legal cannabis. The exception was frequent users (20+ days/month) in medical states, who showed no difference from users in non-legal states.
Why it matters
A common concern about cannabis legalization is that it will increase impaired driving. This study suggests the opposite pattern, at least for self-reported behavior.
The numbers in context
1,249 past-30-day cannabis users. Recreational states: RR 0.41. Medical states: RR 0.39. Frequent users in recreational states: RR 0.70. Frequent users in medical states: RR 0.87 (not significant).
How the study worked
Cross-sectional national survey (2016-2017) of 1,249 past-30-day cannabis users. Logistic regression adjusted for demographics, frequency of use, interaction between use frequency and legal status, calibration weights, and geographic clustering.
What this study cannot tell us
Self-reported driving behavior may be subject to social desirability bias. Cross-sectional design cannot determine causation. 2016-2017 data predates many states' legalization.
How to read the evidence
National sample with appropriate adjustments, but self-report data on impaired driving and cross-sectional design limit conclusions.
When this study was published
Published in 2022 using 2016-2017 survey data.
The bigger picture
The lower rates of self-reported impaired driving in legal states could reflect greater awareness of consequences, availability of delivery services, or cultural shifts in how cannabis is consumed in legal markets.
Questions still open
- What mechanisms explain lower self-reported impaired driving in legal states? Do crash data corroborate these self-report findings?
Common questions
Does cannabis legalization increase impaired driving?
Were frequent users different?
Read the original research
Cannabis legalization and driving under the influence of cannabis in a national U.S. Sample.
Preventive medicine reports, 27, 101799
Citation
Dutra, Lauren M; Farrelly, Matthew; Gourdet, Camille; Bradfield, Brian. (2022). Cannabis legalization and driving under the influence of cannabis in a national U.S. Sample.. Preventive medicine reports, 27, 101799. https://doi.org/10.1016/j.pmedr.2022.101799