Cannabis-intoxicated participants showed decreased theta brain wave power that correlated with worse lane-keeping during simulated driving, suggesting EEG could potentially identify cannabis impairment.
Traffic safety researchers, law enforcement technology developers, cannabis policy analysts
Theta EEG power correlated with impaired lane-keeping under THC but not placebo
What the researchers found
Standard deviation of lane position (SDLP) was significantly worse and heart rate elevated during THC sessions compared to placebo. Theta frequency band (4-7 Hz) EEG power was significantly decreased under THC. Theta power was negatively correlated with SDLP impairment during THC but not placebo sessions.
Why it matters
No validated field test exists for cannabis driving impairment. If EEG biomarkers reliably correlate with impaired driving performance, they could form the basis for objective impairment testing.
The numbers in context
10 subjects; 500mg cannabis at 6.7% THC; SDLP significantly worse under THC; theta power (4-7 Hz) significantly decreased; theta-SDLP correlation significant in dosed condition (no significant EEG-SDLP correlations in placebo condition).
How the study worked
Randomized, crossover, double-blind study with 10 subjects receiving 500mg cannabis (6.7% THC) or placebo via vaporizer. EEG recorded during a 45-minute simulated drive including a 10-minute straight rural road segment. Driving metrics synchronized with EEG data.
What this study cannot tell us
Very small sample (10 subjects); simulated driving rather than real-world conditions; single dose and route of administration; short straight-line driving may not capture all impairment-relevant behaviors.
How to read the evidence
Very small (n=10) crossover trial using simulated driving, not real-world conditions.
When this study was published
Published in 2020.
The bigger picture
As cannabis legalization expands, the lack of a reliable impairment test remains a major challenge for traffic safety. EEG-based approaches represent one possible path forward.
Questions still open
- Would these EEG signatures hold up in larger samples and more complex driving scenarios? Could a portable EEG device be developed for roadside testing?
Common questions
Could an EEG test replace breathalyzers for cannabis?
How did cannabis affect driving in this study?
Read the original research
EEG biomarkers acquired during a short, straight-line simulated drive to predict impairment from cannabis intoxication.
Traffic injury prevention, 21(sup1), S130-S134
Citation
Brown, Timothy L; Richard, Christian; Meghdadi, Amir; Poole, Jared; Fink, Abigail; Stevanović Karić, Marija; McConnell, Marissa; Rupp, Greg; Schmitt, Rose; Gaffney, Gary G; Milavetz, Gary; Berka, Chris. (2020). EEG biomarkers acquired during a short, straight-line simulated drive to predict impairment from cannabis intoxication.. Traffic injury prevention, 21(sup1), S130-S134. https://doi.org/10.1080/15389588.2020.1814957