Study suggests CBD-dominant cannabis may not impair driving performance
Cannabis strains that contain mostly cannabidiol and almost no tetrahydrocannabinol were not significantly associated with impaired driving, according to research published in JAMA.
“The present study shows that cannabis-induced driving impairment varies with cannabis strains,” Johannes Ramaekers, PhD, professor of psychopharmacology and behavioral toxicology at Maastricht University in the Netherlands, told Healio Primary Care.
“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 after use,” he continued.
Previous studies showed that cannabis usage could impair driving performance. One such study, which was conducted among people who were heavy cannabis users, identified impaired driving even when participants had not consumed cannabis.
However, Ramaekers noted that when researchers controlled for self-reported impulsivity, most of the differences between heavy cannabis users and controls were no longer significant, suggesting that the findings from earlier studies assessed the “impact of a personality trait on driving,” rather than the impact of cannabis use on driving.
Ramaekers and colleagues conducted a double-blind, within-participants randomized clinical trial in which participants were assigned to complete driving tests at 40 minutes and 240 minutes after cannabis use.
At each experimental session, participants received vaporized cannabis with 13.75 mg of THC, 13.75 mg of CBD, 13.75 mg of THC and CBD. Participants were randomly assigned to receive different cannabis formulations or placebo at each experimental session.
Prior to their first experimental session, the participants had a practice session to familiarize them with both the driving and cognitive tests. The on-road driving test was approximately 1 hour, and participants drove with licensed drivers in cars with dual controls. To evaluate driving performance, the researchers used standard deviation of lateral position (SDLP), a way to measure lane weaving.
A total of 26 participants completed all eight driving tests in the trial.
Ramaekers and colleagues found that at 40 to 100 minutes, SDLP increased significantly among participants after they consumed THC-dominant cannabis (2.33 cm; 95% CI, 0.80 to 3.86) and cannabis with both THC and CBD (2.83 cm; 95% CI, 1.28 to 4.39), but remained similar with CBD-dominant cannabis (0.05cm; 95% CI, 1.49 to 1.39) compared with placebo.
At 240 to 300 minutes, they determined that the SDLP was not significantly different after consuming CBD-dominant cannabis, THC-dominant cannabis or cannabis with both vs. placebo.
The researchers noted that the observed effect size for CBD-dominant cannabis may not have excluded the occurrence of clinically meaningful impairment and that the doses used in the experimental sessions may not reflect commonly used doses.
In an editorial accompanying the study, Thomas B. Cole, MD, MPH, an associate editor of JAMA, and Richard Saitz, MD, MPH, a professor in the schools of medicine and public health at Boston University, wrote that the findings “challenge the myth that CBD ameliorates the psychoactive/psychomotor effects of THC.”
Cole and Saitz added that additional studies are needed to assess those who regularly use cannabis, the duration of effects at different doses and on driving performance and cognitive tasks at different doses consumed by the general population.
“Clinicians should caution their patients that cannabis products containing equal parts CBD and THC are no less impairing than products containing THC alone,” they wrote.