A small dose of cannabidiol (CBD) does not appear to negatively affect a person’s ability to drive, according to new research published in the Journal of the American Medical Association. But that is not the case for tetrahydrocannabinol (THC), the primary substance responsible for the intoxicating effects of marijuana.
“With increased legalization of cannabis worldwide, there is a concern that the prevalence of driving under the influence of cannabis might increase and put drivers at risk,” said study author Johannes G. Ramaekers, a professor in psychopharmacology at Maastricht University.
His co-author, Iain McGregor, added: “With rapidly changing attitudes towards medical and non-medical use of cannabis, driving under the influence of cannabis is emerging as an important and somewhat controversial public health issue.”
“While some previous studies have looked at the effects of cannabis on driving, most have focused on smoked cannabis containing only THC (not CBD) and have not precisely quantified the duration of impairment,” McGregor explained.
In the placebo-controlled, double-blind study, 26 healthy participants inhaled vaporized cannabis containing different mixes of THC and CBD before their driving performance was assessed in real-world conditions 40 minutes and four hours later.
Driving performance was assessed using a well-established scientific test that measures standard deviation of vehicle position (SDLP), an index of lane weaving, swerving and overcorrecting. SDLP increases under the influence of alcohol and drugs such as Valium.
Each participant completed four experimental sessions that were scheduled at least one week apart, and the order of cannabis doses was randomized.
The researchers found that cannabis containing 13.75mg of THC caused driving impairments measured at 40 minutes later but not after four hours. “This impairment was modest in magnitude and similar to that seen in drivers with” a blood alcohol concentration of 0.05%, the authors of the study said.
However, cannabis that only contained 13.75 mg of CBD had no impact on driving performance and cannabis that contained both THC and CBD produced impairment levels similar to cannabis with THC only.
The finding indicate that people should not drive “for a least 4 hours after smoking a cannabis product that contains THC as well as as CBD,” Ramaekers told PsyPost. “If the cannabis product contains a low dose of CBD and no THC, then the impact on driving is absent.”
“With cannabis laws changing globally, jurisdictions are grappling with the issue of cannabis-impaired driving. These results provide much needed insights into the magnitude and duration of impairment caused by different types of cannabis and can help to guide road-safety policy,” said co-author Thomas Arkell.
But Ramaekers noted that the new study is not the final word on the safety of driving after consuming CBD. “Pharmaceutical applications usually contain much higher doses of CBD than the one tested in our study. Driving studies assessing a wide dose range of CBD should be conducted,” he researcher explained.
The study, “Effect of Cannabidiol and Δ9-Tetrahydrocannabinol on Driving Performance: A Randomized Clinical Trial“, was authored by Thomas R. Arkell, Frederick Vinckenbosch, Richard C. Kevin, Eef L. Theunissen, Iain S. McGregor, and Johannes G. Ramaekers.
