A landmark study has found that cannabidiol, or CBD, an active ingredient in cannabis and the main ingredient in most medicinal marijuana products, does not impair a person’s ability to drive.
Researchers at the Netherlands’ Maastricht University got 26 healthy participants to inhale four types of vaporised cannabis, each containing different mixes of CBD and tetrahydrocannabinol (THC)—the latter being the main psychoactive ingredient in cannabis—on four separate occasions. Then they made them go for a 100-kilometre drive.
Each participant’s driving performance was assessed in real-world conditions along a stretch of public highway, with a driving instructor who was also able to control the vehicle from the passenger seat. Researchers measured the standard deviation of each vehicle’s position—that is, an index of lane weaving, swerving and overcorrecting—during two drives: the first taking place about 40 minutes after the participant huffed the cannabis vapors; the other taking place about four hours after.
While drugs like alcohol, Valium and Stilnox are known to increase the standard deviation of vehicle position, thus making it dangerous to drive, the Maastricht Uni researchers found that CBD did not impair driving. Moderate amounts of THC, meanwhile, mildly impaired participants’ driving ability for up to four hours.
“These findings indicate for the first time that CBD, when given without THC, does not affect a subject’s ability to drive,” said Dr Thomas Arkell, lead author of the study that was published in the Journal of the American Medical Association today. “That’s great news for those using or considering treatment using CBD-based products.”
Both the THC-dominant strain of cannabis and the strain that contained a mixture of THC and CBD affected driving ability most significantly between 40 and 100 minutes after inhalation. Between four and five hours after inhalation, these impairments were mostly found to have worn off.
There was no major difference between the effect that CBD-dominant cannabis had on a participants’ driving ability, and the effect that a placebo had.
The researchers note that the study has several limitations, including the fact that it was limited to healthy volunteers who were occasional cannabis users, and that only one dosage of CBD was tested. It’s not clear whether a lower tolerance or a higher dose might have yielded different results.
As one of the first studies to explore the impacts of CBD on driving ability, though, the findings hold some promise—particularly as medicinal cannabis products become more common around the world.
“With cannabis laws changing globally, jurisdictions are grappling with the issue of cannabis-impaired driving,” Dr Arkell said. “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 … around the world”.
“Road safety is a primary concern. These results should allow for evidence-based laws and regulation for people receiving medical cannabis.”
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