Despite growing evidence that cannabis increases crash risk, fundamental questions about dose-response relationships, tolerance effects, edible impairment timelines, and medical vs recreational user differences remain unresolved.
Policymakers, law enforcement, medical cannabis patients who drive, road safety researchers
Dose-response relationship between cannabis and driving impairment remains unclear
What the researchers found
Cannabis contributes to crash risk, but key questions remain unanswered: the dose-response relationship is unclear, tolerance effects on driving are uncertain, different routes of administration (edibles, vaping) have different impairment timelines, and whether medical users are impaired differently from recreational users is unknown.
Why it matters
Canada and other jurisdictions legalized cannabis with road safety as a central concern, but the evidence needed to inform effective impaired driving policies has significant gaps that urgently need filling.
The numbers in context
Canada legalized non-medical cannabis October 2018; Uruguay in December 2013; evidence covers crash risk, impairment duration, and detection methods
How the study worked
Narrative review identifying and discussing key questions about cannabis and road safety, drawing on epidemiological, behavioral, and pharmacological evidence.
What this study cannot tell us
Many referenced studies use cannabis potencies lower than currently available products. Most driving research involves simulated rather than real-world driving. Sex differences in cannabis pharmacology and driving effects are understudied.
How to read the evidence
Narrative review synthesizing evidence across multiple research domains related to cannabis and road safety
When this study was published
Published in 2021, shortly after Canada became the second country to legalize non-medical cannabis.
The bigger picture
The cannabis-driving research gap is concerning because policies are being implemented based on incomplete evidence. Unlike alcohol, where the dose-response relationship with impairment is well-established, cannabis lacks equivalent scientific foundations for regulation.
Questions still open
- Is there a reliable dose-response curve for cannabis and driving impairment? Should medical cannabis users face the same driving restrictions as recreational users? How do edibles affect driving compared to inhaled cannabis?
Common questions
Does cannabis impair driving?
Are medical cannabis users impaired when driving?
Read the original research
Cannabis, Impaired Driving, and Road Safety: An Overview of Key Questions and Issues.
Frontiers in psychiatry, 12, 641549
Citation
Brands, Bruna; Di Ciano, Patricia; Mann, Robert E. (2021). Cannabis, Impaired Driving, and Road Safety: An Overview of Key Questions and Issues.. Frontiers in psychiatry, 12, 641549. https://doi.org/10.3389/fpsyt.2021.641549