Cannabis Impaired Simulated Driving for Hours, but Users Felt Ready to Drive Too Soon
Smoked cannabis impaired simulated driving for up to 3.5 hours in regular users, but 69% felt ready to drive at 1.5 hours despite continued impairment, suggesting a dangerous false sense of safety.
Quick Facts
What This Study Found
THC significantly impaired the Composite Drive Score at 30 minutes (d=0.59) and 1.5 hours (d=0.55), with borderline impairment at 3.5 hours (d=0.29) and no difference at 4.5 hours. Despite ongoing impairment, 69% of participants reported willingness to drive at 1.5 hours. Neither THC content (5.9% vs 13.4%) nor use intensity predicted driving impairment.
Key Numbers
191 cannabis users; mean age 29.9; mean 16.7 use days/month; Cohen d=0.59 at 30min; d=0.55 at 1.5hr; d=0.29 at 3.5hr; 69% willing to drive at 1.5hr; impairment resolved by 4.5hr
How They Did This
Double-blind, placebo-controlled parallel RCT at UC San Diego. 191 regular cannabis users randomized to placebo, 5.9%, or 13.4% THC smoked ad libitum. Driving simulator assessed at multiple timepoints through 4.5 hours.
Why This Research Matters
This is one of the largest randomized trials of cannabis and driving. The finding that experienced users cannot accurately judge their impairment has critical implications for road safety policies.
The Bigger Picture
As cannabis legalization expands, determining safe wait times before driving is essential. This study suggests impairment persists longer than users perceive, with a dangerous gap between felt readiness and actual performance.
What This Study Doesn't Tell Us
Simulated driving, not real-world. Cannabis smoked ad libitum may not replicate all consumption patterns. Regular users only, so results may not apply to occasional users.
Questions This Raises
- ?Should cannabis products carry minimum wait-time warnings before driving?
- ?Would different consumption methods (edibles, vaping) produce different impairment timeframes?
Trust & Context
- Key Stat:
- 69% felt ready to drive despite ongoing impairment
- Evidence Grade:
- Well-designed double-blind RCT with 191 participants, multiple timepoints, and objective driving measures.
- Study Age:
- Published in 2022
- Original Title:
- Driving Performance and Cannabis Users' Perception of Safety: A Randomized Clinical Trial.
- Published In:
- JAMA psychiatry, 79(3), 201-209 (2022)
- Authors:
- Marcotte, Thomas D(13), Umlauf, Anya(5), Grelotti, David J(6), Sones, Emily G, Sobolesky, Philip M, Smith, Breland E, Hoffman, Melissa A, Hubbard, Jacqueline A, Severson, Joan, Huestis, Marilyn A, Grant, Igor, Fitzgerald, Robert L
- Database ID:
- RTHC-04040
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
How long does cannabis impair driving?
This RCT found significant impairment at 30 minutes and 1.5 hours after smoking, borderline impairment at 3.5 hours, and no impairment at 4.5 hours. The authors suggest most users should wait at least 4.5 hours before driving.
Does stronger cannabis impair driving more?
Surprisingly, no. When experienced users controlled their own intake, driving impairment was similar whether they smoked 5.9% or 13.4% THC cannabis, suggesting users titrate their dose regardless of potency.
Read More on RethinkTHC
- 420-sober-survival-guide
- CBT-cannabis-recovery
- cannabis-dependence-physical-psychological-addiction-science
- cannabis-perception-vs-evidence-gap
- cannabis-relapse-cycle-pattern
- cannabis-use-disorder-test
- cold-turkey-vs-taper-quit-weed
- cross-addiction-quit-weed-start-drinking
- dating-sober-after-quitting-weed
- exercise-quitting-weed-anxiety-brain
- grieving-quitting-weed-loss
- help-someone-quit-weed
- how-to-quit-weed
- is-weed-addictive
- is-weed-addictive-science
- 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-and-alcohol
- 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
- rehab-for-weed-addiction-necessary
- relapsed-smoking-weed-what-to-do
- relapsed-weed
- should-i-quit-weed
- signs-of-cannabis-use-disorder
- 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
- weed-vape-pen-addiction
Cite This Study
https://rethinkthc.com/research/RTHC-04040APA
Marcotte, Thomas D; Umlauf, Anya; Grelotti, David J; Sones, Emily G; Sobolesky, Philip M; Smith, Breland E; Hoffman, Melissa A; Hubbard, Jacqueline A; Severson, Joan; Huestis, Marilyn A; Grant, Igor; Fitzgerald, Robert L. (2022). Driving Performance and Cannabis Users' Perception of Safety: A Randomized Clinical Trial.. JAMA psychiatry, 79(3), 201-209. https://doi.org/10.1001/jamapsychiatry.2021.4037
MLA
Marcotte, Thomas D, et al. "Driving Performance and Cannabis Users' Perception of Safety: A Randomized Clinical Trial.." JAMA psychiatry, 2022. https://doi.org/10.1001/jamapsychiatry.2021.4037
RethinkTHC
RethinkTHC Research Database. "Driving Performance and Cannabis Users' Perception of Safety..." RTHC-04040. Retrieved from https://rethinkthc.com/research/marcotte-2022-driving-performance-and-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.