Vaporizing low-THC/CBD-rich cannabis (<1% THC) did not impair driving-related ability compared to placebo, but THC was detectable in blood for up to 5 hours, potentially creating legal problems for drivers.
Read this if you use CBD products and drive, or are interested in the regulatory gap between legal CBD and driving THC limits.
Up to 5 hoursTHC remained detectable in blood after vaping legal CBD-rich cannabis with <1% THC
What the researchers found
In this double-blind, randomized, crossover trial, participants vaped two CBD-rich cannabis products (both <1% THC, ~38-39mg CBD) and placebo. Computerized driving tests showed no significant differences between CBD-rich products and placebo. However, THC was detected in blood after both products, with peak levels and detection duration depending on THC content. After single use, THC dropped below 1.5 µg/L after 1.5 hours but remained detectable in some participants up to 5 hours.
Why it matters
CBD products are legal in many jurisdictions, but this study reveals a practical problem: legal CBD-rich cannabis can produce detectable blood THC levels that may exceed driving thresholds, even though no actual impairment occurs.
The numbers in context
- Product 1: 38mg CBD, 1.8mg THC
- Product 2: 39mg CBD, 0.6mg THC
- Both products: <1% THC
- 27 completed single-dose arm; 20 completed repeat-dose arm
- Mean age: 28.9±12.5 (S1), 25.2±4.0 (S2)
- THC <1.5 µg/L after 1.5h (single use)
- THC detectable up to 5h in some participants
- No significant driving impairment vs placebo
How the study worked
Prospective, placebo-controlled, double-blind, randomized, crossover study. Participants vaped two CBD-rich products and placebo. Blood cannabinoid levels measured serially. Driving ability assessed by computerized tests. Single-dose and repetitive-dose arms.
Who was studied
Healthy adult volunteers with smoking experience (27 single-dose, 20 repetitive-dose)
What this study cannot tell us
Computerized driving tests may not capture all aspects of real-world driving. Small sample size. Participants were experienced smokers. Legal THC thresholds vary by jurisdiction.
How to read the evidence
Randomized double-blind crossover trial. Strong internal validity for demonstrating both the absence of impairment and the presence of detectable THC.
When this study was published
Published in 2023. Directly relevant to current CBD product regulation and driving legislation.
The bigger picture
As CBD products gain mainstream adoption, the disconnect between "legal product" and "positive THC blood test" creates real-world consequences for drivers. Policy needs to account for the trace THC in legal CBD products.
Questions still open
- Should driving-related THC thresholds be adjusted for CBD product users?
- Do repeated daily CBD use patterns lead to higher cumulative THC levels?
- Could oral CBD products avoid the THC detection issue better than vaporized products?
Read the original research
Effect of vaporizing cannabis rich in cannabidiol on cannabinoid levels in blood and on driving ability - a randomized clinical trial.
International journal of legal medicine, 137(6), 1713-1723
Citation
Egloff, Laura; Frei, Priska; Gerlach, Kathrin; Mercer-Chalmers-Bender, Katja; Scheurer, Eva. (2023). Effect of vaporizing cannabis rich in cannabidiol on cannabinoid levels in blood and on driving ability - a randomized clinical trial.. International journal of legal medicine, 137(6), 1713-1723. https://doi.org/10.1007/s00414-023-03076-0