A landmark study on how cannabis affects driving ability has shown that cannabidiol (CBD), a cannabis component now widely used for medical purposes, does not impair driving, while moderate amounts of the main intoxicating component tetrahydrocannabinol (THC) produce mild driving impairment lasting up to four hours.
The study was led the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney and conducted at Maastricht University in the Netherlands. It was published today in the prestigious Journal of the American Medical Association.
The research involved people inhaling vaporised cannabis containing different mixes of THC and CBD, then going for a 100-kilometre drive under controlled conditions on public highways both 40 minutes and four hours later. Cannabis containing mainly CBD did not impair driving while cannabis containing THC, or a THC/CBD mixture, caused mild impairment measured at 40 minutes later but not after four hours.