Meta-analysis of 57 studies confirmed cannabis impairs driving, comparable to low blood alcohol
A meta-analysis of 57 driving studies with 1,725 participants found cannabis impairs lateral vehicle control and that combining cannabis with alcohol produces greater impairment than either substance alone.
Quick Facts
What This Study Found
Cannabis alone impaired lateral control (lane weaving) and decreased driving speed. Cannabis combined with alcohol produced greater driving impairment than either substance alone. Cannabis effects on driving were similar to low blood alcohol concentrations.
Key Numbers
57 studies, 1,725 participants. Cannabis lateral position variability: g=0.331. Lane excursions: g=0.198. Cannabis+alcohol vs alcohol alone: g=0.480 for lateral variability, g=0.525 for time out of lane. Cannabis+alcohol vs cannabis alone: g=0.336 for lateral variability.
How They Did This
Systematic review and meta-analysis of 57 experimental driving studies (simulator, closed-course, on-road) involving cannabis and/or alcohol administration with 1,725 participants. Searched 9 databases. Used Hedges' g effect sizes.
Why This Research Matters
This is the largest meta-analysis of experimental driving studies on cannabis to date, providing definitive evidence that cannabis impairs driving performance and that the combination with alcohol is particularly dangerous.
The Bigger Picture
As cannabis legalization expands, quantifying exactly how much it impairs driving, both alone and combined with alcohol, is essential for setting evidence-based impaired driving policies.
What This Study Doesn't Tell Us
Most studies used driving simulators rather than on-road conditions. Study heterogeneity limited interpretation of some measures. THC doses and timing varied across studies.
Questions This Raises
- ?At what THC blood concentration does driving impairment become equivalent to the legal alcohol limit?
- ?How long after cannabis use does driving impairment persist?
- ?Should combined substance use carry enhanced legal penalties?
Trust & Context
- Key Stat:
- Cannabis+alcohol worse than either substance alone
- Evidence Grade:
- Strong: large meta-analysis of 57 experimental studies with direct driving performance measures.
- Study Age:
- Published in 2022.
- Original Title:
- The effects of cannabis and alcohol on driving performance and driver behaviour: a systematic review and meta-analysis.
- Published In:
- Addiction (Abingdon, England), 117(7), 1843-1856 (2022)
- Authors:
- Simmons, Sarah M(2), Caird, Jeff K, Sterzer, Frances, Asbridge, Mark
- Database ID:
- RTHC-04224
Evidence Hierarchy
Combines results from multiple studies to find an overall pattern.
What do these levels mean? →Frequently Asked Questions
How does cannabis driving impairment compare to alcohol?
Cannabis effects on driving performance were similar to low blood alcohol concentrations, primarily affecting lateral vehicle control (lane weaving) and causing drivers to slow down.
Is combining cannabis and alcohol especially dangerous?
Yes. The combination produced significantly greater driving impairment than either substance alone, with larger effect sizes for lateral position variability and time spent out of lane.
Did cannabis affect all aspects of driving equally?
No. Cannabis primarily impaired lateral control (staying in lane) and caused decreased speed. Effects on hazard response time and other measures were less consistent across studies.
Read More on RethinkTHC
- 420-sober-survival-guide
- CBT-cannabis-recovery
- cannabis-relapse-cycle-pattern
- cold-turkey-vs-taper-quit-weed
- dating-sober-after-quitting-weed
- exercise-quitting-weed-anxiety-brain
- grieving-quitting-weed-loss
- help-someone-quit-weed
- how-to-quit-weed
- journaling-weed-withdrawal
- marijuana-anonymous-SMART-recovery-compare
- meditation-mindfulness-weed-withdrawal
- partner-still-smokes-weed
- partner-still-smokes-weed-quitting
- pink-cloud-sobriety-cannabis
- quit-weed-cold-turkey
- quit-weed-or-cut-back-which-is-better
- quit-weed-regret-went-back
- quitting-weed-20s
- quitting-weed-30s
- quitting-weed-after-years
- quitting-weed-during-crisis-divorce-job-loss
- quitting-weed-exercise
- quitting-weed-grief-loss-coping
- quitting-weed-legal-state
- quitting-weed-success-stories
- quitting-weed-triggers-environment
- relapsed-smoking-weed-what-to-do
- relapsed-weed
- should-i-quit-weed
- sober-music-festival-concert-without-weed
- supplements-weed-withdrawal
- telling-friends-quitting-weed
- weed-relapse-prevention-plan
- weed-relapse-why-it-happens
- weed-ritual-replacement
- weed-ruined-relationships
- weed-social-media-triggers-quit
Cite This Study
https://rethinkthc.com/research/RTHC-04224APA
Simmons, Sarah M; Caird, Jeff K; Sterzer, Frances; Asbridge, Mark. (2022). The effects of cannabis and alcohol on driving performance and driver behaviour: a systematic review and meta-analysis.. Addiction (Abingdon, England), 117(7), 1843-1856. https://doi.org/10.1111/add.15770
MLA
Simmons, Sarah M, et al. "The effects of cannabis and alcohol on driving performance and driver behaviour: a systematic review and meta-analysis.." Addiction (Abingdon, 2022. https://doi.org/10.1111/add.15770
RethinkTHC
RethinkTHC Research Database. "The effects of cannabis and alcohol on driving performance a..." RTHC-04224. Retrieved from https://rethinkthc.com/research/simmons-2022-the-effects-of-cannabis
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.