Researchers from the Lambert Initiative at the University of Sydney, have found that cannabidiol, a medically active compound found in cannabis, does not affect driving ability. They also found that moderate tetrahydrocannabinol (THC) intoxication leads to mild drivingimpairment that wears off within four hours.
For the study, the researchers recruited 26 healthy participants at their testing site at Maastricht University in the Netherlands. Each were given four different types of cannabis with varying ratios of CBD and THC, including a placebo, at random to vaporize on four different occasions.
Each participant's ability to drive was then assessed on the road in real-life conditions. Altogether, they drove 100 kilometers on a public highway in a dual-control car under the supervision of a driving instructor.
To assess each particpant's driving, the researchers used a well-known scientific driving test that measures standard deviation of vehicle position (SDLP), an index of lane weaving, swerving and overcorrecting. Participants were assessed at 40 minutes and four hours after inhaling vaporized cannabis.
All in all, the researchers found that cannabis containing CBD had no effect on driving, whereas that containing THC, or a mixture of CBD and THC mildly impaired driving 40 minutes after vaporization. After four hours, those who consumed THC had no impairment.
"With cannabis laws changing globally, jurisdictions are grappling with the issue of cannabis-impaired driving. 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 not just in Australia but around the world," says Dr. Thomas Arkell, lead author of the study.
"Studying the effects of cannabis on driving with such precision in a real-world context is incredibly important," says Professor Iain McGregor, Academic Director of the Lambert Initiative. "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."