Almost all cannabis driving research has used ~6% THC products, while today's market sells flower exceeding 20% THC and concentrates above 60%, creating a large gap between research and reality.
Driving safety researchers, policymakers, forensic scientists, anyone interested in cannabis impairment evidence
Research uses ~6% THC while commercial products exceed 20-60% THC
What the researchers found
Nearly all driving impairment studies used inhaled cannabis at approximately 6% THC, far below the 20%+ THC flower and 60%+ THC concentrates now sold commercially. The dose-response relationship at higher potencies and the impairment timeline for different administration routes (edibles, vaping) remain largely unstudied.
Why it matters
If driving research only tests products a fraction of the potency people actually use, the real-world impairment from modern cannabis products may be significantly underestimated, leaving a dangerous gap in safety knowledge.
The numbers in context
Research typically uses ~6% THC; commercial flower can exceed 20% THC; extracts can contain 60%+ THC; crash risk increases approximately 2-fold after smoking marijuana
How the study worked
Systematic review following PRISMA guidelines of PubMed literature and grey literature (congressional reports, committee reports, roadside surveys) on cannabis impairment and driving performance modeling.
What this study cannot tell us
Federal restrictions on cannabis research have limited access to products matching commercial potency. Many studies use vaporized rather than smoked cannabis. Naturalistic driving studies introduce uncontrollable variables.
How to read the evidence
Systematic review identifying critical gaps between research conditions and real-world cannabis products
When this study was published
Published in 2021. Cannabis potency continues to increase in commercial markets.
The bigger picture
The mismatch between research cannabis and commercial cannabis undermines the evidence base for both driving laws and public safety messaging about cannabis impairment.
Questions still open
- Does higher potency cannabis produce proportionally more driving impairment? How does the extended impairment timeline from edibles compare to inhalation? Can existing impairment models be recalibrated for modern-potency products?
Common questions
How does cannabis affect driving?
Why is there a gap between cannabis research and reality?
Read the original research
Mechanisms of cannabis impairment: Implications for modeling driving performance.
Forensic science international, 328, 110902
Citation
Burt, Thomas S; Brown, Timothy L; Milavetz, Gary; McGehee, Daniel V. (2021). Mechanisms of cannabis impairment: Implications for modeling driving performance.. Forensic science international, 328, 110902. https://doi.org/10.1016/j.forsciint.2021.110902