CBD doesn't impair driving, clinical trial finds

January 15, 2021

It's OK to vape and drive, a new study finds. (Unsplash/Clear Cannabis)

Participants who vaped a standard dose of CBD-dominant cannabis did not exhibit impaired driving in a recent study measuring the effects of the less-examined cannabidiol compound found in marijuana.

As weed is more widely legalized for medical and recreational use around the United States and the world, the research published last month in JAMA aims to help address a dearth of evidence regarding the safety of CBD, whose counterpart compound tetrahydrocannabinol, or THC, produces the plant’s intoxicating effects. 

Previous literature has associated cannabis with a higher risk of car crashes, but examinations of how it affects driving performance have focused on THC or the whole marijuana plant. Some studies have further suggested that CBD, sometimes prescribed to treat epilepsy, psychosis and neurological disorders, compensates for the effects of THC, which can include anxiety, paranoia and cognitive impairment.

“Even though we knew that cannabis itself can affect driving, we were unsure whether this would hold true for any particular strain that you now can find on the market,” explained the study’s principal investigator and last author Johannes G. Ramaekers, a professor of pharmacology and behavioral toxicology at Maastricht University in the Netherlands. 

For the double-blind randomized clinical trial, researchers measured the extent to which 26 healthy participants who were occasional cannabis users weaved lanes, swerved and overcorrected on the road during 62-mile driving tests. The effects of vaporizing a 13.75 mg dose were gauged through a “standard deviation of lateral position,” also called SDLP, with the lateral position marking the distance from the vehicle to the left-hand lane boundary.

The drivers drove twice: 40 minutes and four hours after vaping a placebo, CBD-dominant cannabis, THC-dominant cannabis or hybrid strain with equal parts of the two compounds. Each person completed the exercise four times between May 2019 and March 2020.

Participants who vaped the CBD-dominant strain swayed less drastically from the lateral position than did any other drivers, with an average SDLP of 18.21 centimeters when driving at 40 to 100 minutes after consumption.

In contrast, THC-dominant and hybrid vapers had SDLPs of 20.59 centimeters and 21.09 centimeters, respectively. The result for placebo cannabis was 18.28 centimeters.

The takeaway, the study says, is that relative to placebo, “SDLP was significantly increased by THC-dominant cannabis … and THC/CBD-equivalent cannabis,” but not the CBD-dominant strain. “CBD-dominant cannabis also failed to produce significant cognitive or psychomotor impairment compared with placebo.”

Regarding the effects of THC, the study notes, “This impairment was modest in magnitude and similar to that seen in drivers with a 0.05% blood alcohol content.”

Researchers also sought to understand how long one must wait to drive safely after smoking.

Once 240 to 300 minutes had passed, the same pattern remained among drivers: The SDLP was 19.03 centimeters with CBD-dominant cannabis, 19.88 centimeters with THC-dominant, 20.59 centimeters for the hybrid and 19.37 centimeters for the placebo. But in this case, no SDLP differed significantly from the placebo.

“I think it was a very good confirmation of expectations that we would have,” Ramaekers said. “But nobody had actually firmly demonstrated the presence or the absence of effects for these two compounds.”

The relatively low amount vaped could be considered “a normal dose,” but in practice, dosage sizes can vary, including in retail CBD products in North America and elsewhere that aren’t strictly regulated.

“Driving outcomes may differ with higher CBD and THC doses and different CBD:THC ratios,” the study said. “The applicability of these findings to more frequent users, including medical cannabis patients, is unclear given that daily cannabis use may produce at least partial tolerance to the impairing effects of THC.” 

Additionally, medical CBD doses can be up to 87 times larger than those examined in the study, Ramaekers pointed out.

“For the recreational user that would not automatically take so much CBD as in a medical context, I think this is valuable information,” he said. “But in the end, of course, the responsibility is always with the individual and the individual driver. If somebody feels impaired then they simply should not drive.” 

The findings carry implications for regulators, said Ramaekers, who is president of the International Council on Alcohol, Drugs and Traffic Safety. Although cannabis is essentially regulated as a single product, the market has expanded to include concentrates, edibles and other products that are freely available, particularly in the U.S.

“I think we are now at a junction where you see that traditional cannabis will always be there, but there will be so much variation and so much spinoff of that particular plant, that probably legislation will have to follow and also regulation will have to follow and make sure that they are not prosecuting people in cars that have just smoked CBD rather than THC,” Ramaekers said.

The study was funded by the University of Sydney’s Lambert Initiative for Cannabinoid Therapeutics, an independent research center that works to advance CBD-based treatments in mainstream medicine.

The study “Effect of Cannabidiol and Δ9-Tetrahydrocannabinol on Driving Performance: A Randomized Clinical Trial,” published Dec. 1 in JAMA, was authored by Thomas R. Arkell, University of Sydney and Maastricht University; Frederick Vinckenbosch, Maastricht University; Richard C. Kevin, University of Sydney; Eef L. Theunissen, Maastricht University; Iain S. McGregor, University of Sydney; and Johannes G. Ramaekers, Maastricht University.

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