Study finds that using CBD alone has no negative impact on driving ability
Researchers say they have determined that using CBD does not impair driving performance and consuming moderate amounts of THC produces only mild impairment lasting up to four hours.
That’s the conclusion of a new study that involved 26 healthy participants inhaling vaporized cannabis containing different mixes of THC and CBD before driving 100 kilometres under controlled conditions on public highways. The subjects received weed containing mainly THC (enough to cause strong feelings of intoxication), mainly CBD, both THC and CBD or placebo pot, notes a press release from the University of Sydney.
Using the four different types of cannabis in random order, the hour-long drives in a dual-control car with a driving instructor present were taken 40 minutes and four hours after consumption. The standard deviation of vehicle position (called SDLP) measures considered in testing driving ability included lane weaving, swerving and over-correcting.
Specifically, the study, published in the Journal of the American Medical Association,found that weed containing mainly CBD did not impair driving performance. With cannabis containing THC or a THC/CBD mixture, there was mild impairment at the 40-minute drive mark, but not after four hours.
“The SDLP following vaporized THC-dominant and THC/CBD-equivalent cannabis compared with placebo was significantly greater at 40 to 100 minutes, but not 240 to 300 minutes after vaporization,” the study states. “There were no significant differences between CBD-dominant cannabis and placebo,” authors write.
Led by the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney in Australia and conducted at Maastricht University in the Netherlands, “these findings indicate for the first time that CBD, when given without THC, does not affect a subject’s ability to drive,” lead author Thomas Arkell, Ph.D., says in the statement.
Lead author Thomas Arkell, Ph.D. / PHOTO BY UNIVERSITY OF SYDNEY
With CBD increasingly being used for medical purposes — such as epilepsy, anxiety, chronic pain and addictions — the results are “great news for those using or considering treatment using CBD-based products,” Arkell suggests.
Emphasizing that road safety is the primary concern, the findings “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 not just in Australia, but around the world,” he suggests.
“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,” notes Professor Iain McGregor, academic director of the Lambert Initiative.
Acknowledging that other studies looking at cannabis and driving have been done, McGregor nonetheless says this is the first research “to illustrate the lack of CBD effects on driving and to also provide a clear indication of the duration of THC impairment.”
Professor Iain McGregor, academic director of the Lambert Initiative. / PHOTO BY UNIVERSITY OF SYDNEY
Citing results of its Road Safety Monitor, Canadian-based Traffic Injury Research Foundation (TIRF) recently noted that “driving within two hours of using marijuana remains problematic as shown in the level of public concern two years post-legalization in Canada.”
Although drivers have continued to use cannabis since recreational weed was legalized in the country two years ago, “fewer drivers did so in 2020 as compared to 2019,” TIRF reports. Specifically, 4.5 per cent of drivers admitted to driving within two hours of using recreational marijuana in 2020, down from about 7.0 per cent in 2019, but higher than the 3.3 per cent in 2018.
“The decline since 2019 may indicate education and enforcement initiatives are having an effect on driver behaviour, but clearly some continue to make choices that create risk for all road users,” TIRF research scientist Heather Woods-Fry says in a statement.
Example of standard deviation of lateral position. Image from Verster and Roth (2011) International Journal of General Medicine. / University of Sydney
And a study published earlier this year in Drug and Alcohol Dependence found that “cannabis users had poorer driving simulator performance relative to controls.”
Health Canada’s advice when it comes to consuming cannabis and driving? Just don’t do it. Noting that individual impairment can depend on the method of consumption, the amount consumed and THC levels (including cannabis prescribed for medical use), “there is no guidance to drivers about how much cannabis can be consumed before it is unsafe to drive or how long a driver should wait to drive after consuming cannabis,” the federal department reports.
Abstaining is also recommended as part of a new Canadian Automobile Association educational campaign focusing on edibles, which are known to take longer to kick in and whose related highs can be intense.
Accurate product labelling will be paramount. / Getty Images PHOTO BY GETTY IMAGES
As is already the case, accurate product labeling will be paramount. Depending on the source of cannabis, there have been plenty of examples of hemp, which could be used to make CBD products, having too high a THC level.
Earlier this year in Arizona, for example, the state’s Department of Agriculture reported that about 41 per cent of the plants it analyzed failed to keep THC levels below the legal requirement of 0.3 per cent. In both the U.S. and Canada, if the plant has more than that level of THC, it is considered cannabis.
Additionally, there can be problems with how much THC is said to be included in products. Health Canada reported last June that it had been flagging legal cannabis products containing incorrect amounts of THC content, according to the Calgary Herald.These amounts have been as much as five times higher than advertised.
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