Small doses of CBD do not appear to have a significant effect on driving, according to the first study of its kind published last week in the Journal of the American Medical Association.
However, similar doses of THC were associated with short-term driving impairment, “small in magnitude and similar to that observed in drivers with 0.05%” blood alcohol concentration. According to the study, the “impairment” caused by marijuana use disappears after about four hours.
The experiment, conducted by the University of Sydney, is the latest study on the effects of CBD and THC consumption on drivers. The topic is of growing public interest as more and more countries and states around the world liberalise laws related to cannabis use.
“The results should reassure people using CBD-only products as they are safe for driving, while they may also help patients using THC-dominant products to know when to get behind the wheel,” said Iain McGregor, academic director of the Lambert Initiative for Cannabinoid Therapeutics
The new study was funded by the Lambert Initiative, which studies the health effects of cannabis, and was conducted at Maastricht University in the Netherlands. To measure the effects of cannabinoids on drivers, researchers first had participants calibrate one of four cannabis blends: predominantly THC, predominantly CBD, a combination of two cannabinoids, or a placebo containing less than 0.2% total cannabinoids. The target dose for each cannabinoid other than placebo was 13.75 milligrams.
The subjects then got into their cars and hit the road. Accompanied by a licensed driving instructor, each covered a 100-kilometre stretch on a Dutch motorway twice: the first time 40 minutes after consuming the cannabis mixture and again four hours after ingestion.
Researchers measured impaired driving ability by tracking how often drivers invaded lane separation lines (SDLPs). Participants were also tested in a laboratory setting for cognitive and psychomotor performance, blood levels of cannabinoids, as well as heart rate and blood pressure.
Consuming CBD alone has no effect on driving
“There were no significant differences between CBD-dominant cannabis and placebo,” – reads the study. “The frequency of driving on roadway separation lines (SDLP) under placebo and CBD conditions did not differ, indicating that CBD did not adversely affect driving.”
“These findings indicate for the first time that CBD given without THC does not affect driving ability,” – Thomas Arkell, lead author of the study, said.
Participants who consumed THC or a mixture of cannabinoids showed a moderate but statistically significant impairment in driving ability during their first test drive, reporting driving-over-the-lines values similar to drivers with a blood alcohol concentration of 0.05%.
Unlike many drunk drivers, the subjects who consumed THC or a THC-CBD mixture seemed clearly aware of the risks behind the wheel. This effect persisted, even as the visible signs of THC’s effects faded.
The subjects described themselves as “significantly more impaired” after consuming THC or both cannabinoids, with reduced self-confidence being the main complaint. However, after testing, most subjects were able to correctly observe that their driving quality was worse during the first test.
“Participants believed that for 240-300 minutes after consuming THC or THC+CBD, their driving ability was more impaired than after consuming placebo,” – the authors write.
The second test began four hours after ingestion, which the researchers say indicates the time at which THC’s effect on driving wears off.
“Previous roadside and simulation studies have described increased levels of SDLP (running over lines separating roadway lanes – ed.) up to three hours after cannabis inhalation,” the study reads. “The present study did not detect SDLP after 4-5 hours.
This does not mean that consumers must necessarily assume they can drive after just four hours. Higher doses or edible products with THC may prolong the duration of impairment, “so these results should not be considered definitive”.
Similar limitations may apply to results for CBD. The authors note that the target dose of 13.75 mg in the study is much lower than what is typically given for some therapies, such as the treatment of drug-resistant epilepsy. “Results may vary with higher doses of CBD and THC and different CBD: THC ratios,” – they write.
Nevertheless, the authors said, these studies offer valuable data about how marijuana affects drivers, or, as in some cases, apparently does not affect drivers…
Nevertheless, if you are looking for driving lessons in Southampton, a good option is to choose Adam Driving School.