How stoned drivers feel predicts driving performance beyond THC dose alone, but the specific predictors vary
In a 52-person driving study, self-reported subjective effects of cannabis predicted driving performance beyond what THC dosing alone could explain, but the specific subjective feelings that mattered varied between studies.
Quick Facts
What This Study Found
Subjective perceptions of cannabis impairment significantly predicted driving performance measures (lane position, speed control) beyond the effect of THC dose. Feeling "stoned" was a perfectly consistent predictor across both this and a prior study. However, other subjective measures like "anxious," "good drug effect," and "restless" were inconsistent across studies, suggesting individual variability in the subjective-performance relationship.
Key Numbers
52 subjects; placebo vs. 6.18% THC; "stoned" was a perfectly consistent predictor across both studies. "High" and "sedated" had one mismatch each. "Anxious," "good drug effect," and "restless" had three or more mismatches.
How They Did This
52 subjects completed a driving performance study with placebo vs. 6.18% THC cannabis. SAS GLM Select with stepwise selection analyzed relationships between subjective effects, dosing condition, and driving performance. Results compared to a prior 10-subject study.
Why This Research Matters
If subjective feelings predict driving impairment better than blood THC levels, this has implications for impaired driving enforcement and personal decision-making about driving after cannabis use.
The Bigger Picture
The inconsistency of subjective predictors between studies mirrors the challenge of cannabis-impaired driving enforcement: there is no simple equivalent of "I feel drunk" that reliably predicts impairment.
What This Study Doesn't Tell Us
Relatively small sample. Only one THC dose tested. Simulator driving may not reflect real-world conditions. Subjective measures are inherently variable. Comparison study had only 10 subjects.
Questions This Raises
- ?Could a validated subjective impairment scale be developed for cannabis?
- ?Would combining subjective reports with objective measures (like eye tracking) improve impairment detection?
- ?Does tolerance affect the subjective-performance relationship?
Trust & Context
- Key Stat:
- "Stoned" was the only perfectly consistent predictor of driving impairment
- Evidence Grade:
- Controlled driving study with replication attempt, but inconsistencies between studies limit generalizability.
- Study Age:
- Published in 2022.
- Original Title:
- Perceived effects of cannabis: Generalizability of changes in driving performance.
- Published In:
- Traffic injury prevention, 23(sup1), S8-S13 (2022)
- Authors:
- Burt, Thomas S(3), Brown, Timothy L(6), Schmitt, Rose(6), McGehee, Daniel, Milavetz, Gary, Gaffney, Gary, Berka, Chris
- Database ID:
- RTHC-03735
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
Can drivers accurately tell if they are too impaired from cannabis to drive?
Subjective feelings predicted driving performance in this study, but the specific feelings that mattered varied. "Stoned" was the most reliable predictor, while feelings like "anxious" or "good drug effect" were inconsistent, suggesting self-assessment is imperfect.
Is THC blood level a good predictor of driving impairment?
THC dose alone predicted some driving impairment, but subjective effects explained additional variability in performance that blood levels could not, suggesting impairment is influenced by individual factors beyond just how much THC is in the blood.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-03735APA
Burt, Thomas S; Brown, Timothy L; Schmitt, Rose; McGehee, Daniel; Milavetz, Gary; Gaffney, Gary; Berka, Chris. (2022). Perceived effects of cannabis: Generalizability of changes in driving performance.. Traffic injury prevention, 23(sup1), S8-S13. https://doi.org/10.1080/15389588.2022.2128787
MLA
Burt, Thomas S, et al. "Perceived effects of cannabis: Generalizability of changes in driving performance.." Traffic injury prevention, 2022. https://doi.org/10.1080/15389588.2022.2128787
RethinkTHC
RethinkTHC Research Database. "Perceived effects of cannabis: Generalizability of changes i..." RTHC-03735. Retrieved from https://rethinkthc.com/research/burt-2022-perceived-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.