According to the results of a new research study, CBD low-dose does not impair driving, while consuming moderate amounts of THC results in mild to strong, short-lived impairment, lasting up to four hours. The results of the study, led by researchers the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney in Australia and conducted at Maastricht University in the Netherlands, can help to guide road safety policy.
The study included 26 healthy participants who inhaled vaporized cannabis containing different mixes of THC and CBD before driving 100 kilometres on public highways under controlled conditions. The subjects received four types of vaporized mix – containing THC (at a sufficient concentration to result in strong intoxication), CBD, both THC and CBD, or placebo.
Four hours later, the study participants took a second drive. At various points during the experiment, they were administered several tests to evaluate their cognition. The researchers measured participants’ driving ability by examining the standard deviation of vehicle position and scoring drivers’ lane weaving, swerving and over-correcting.
The results showed that when THC was inhaled by participants, whether by itself or with CBD, they experienced mild to strong intoxication affecting their driving scores, which seemed to fade after four hours. However, inhaling the mixture with CBD as the primary ingredient did not significantly impair their driving ability.
“These findings indicate for the first time that CBD, when given without THC, does not affect a subject’s ability to drive,” said Thomas Arkell, the study’s first author and cannabinoid therapeutics researcher at the University of Sydney.
These results confirm previous results collected by the Canadian-based Traffic Injury Research Foundation (TIRF), which has stated that “driving within two hours of using marijuana remains problematic as shown in the level of public concern two years post-legalization in Canada.” In addition, according to TIRF, fewer drivers have consumed cannabis prior to driving in 2020 as compared to 2019.
The study’s authors had expressed hope that their findings offer real-world data about how cannabis affects drivers.
“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,” said McGregor. “This is the first study to illustrate the lack of CBD effects on driving and to also provide a clear indication of the duration of THC impairment.”
Moreover, McGregor added that the results of the study can help to guide road safety policy. “The results should reassure people using CBD-only products that they are most likely safe to drive, while helping patients using THC-dominant products to understand the duration of impairment… The implication for the general public is that the cannabis-induced driving impairment should be acknowledged as a public health risk, while taking into account that impairment may differ between cannabis strains and depends on time [elapsed] after use,” he stated in a media release.
