A landmark study suggests that CBD-only cannabis and hemp products do not impact driving ability – a finding with implications for drug-driving laws internationally.
Using a real-world road test, researchers from the University of Sydney in Australia and the Maastricht University in the Netherlands found that unlike tetrahydrocannabinol (THC), cannabidiol (CBD) does not cause driving impairment.
Both THC and CBD are major components of cannabis and are being extensively researched and used for a wide range of health benefits. However, CBD specifically has garnered significant medical attention because unlike THC, using CBD does not result in euphoria or intoxication.
While CBD is known to be non-intoxicating, no study had yet confirmed whether it would influence a person’s ability to drive.
Results from the clinical study showed “no significant differences [in driving performance] between CBD-dominant cannabis and placebo.”
“These findings indicate for the first time that CBD, when given without THC, does not affect a subject’s ability to drive,” said study lead author, Thomas Arkell. “That’s great news for those using or considering treatment using CBD-based products.”
Tests Done Under Real-Road Conditions
Double-blind and randomized driving tests were done on a 100 km stretch of public highway with a certified driving instructor to mimic, as closely as possible, real-world driving conditions.
“Road safety is a primary concern,” Arkell said. “These results should allow for evidence-based laws and regulation for people receiving medical cannabis.”
Participants were invited to vaporize either THC, CBD, or a THC/CBD blend and researchers compared their driving to participants who took a placebo. Researchers used a THC or CBD dose of 13.75 mg, which was enough to cause strong feelings of intoxication.
To measure whether their driving was impaired, the team calculated the car’s standard deviation of vehicle Position (SDLP) – a measurement of the drivers’ overall lane weaving, swerving, and overcorrecting.
When individuals are under the influence of alcohol or psychoactive drugs, their SDLP will increase.
While CBD had no significant impact on the participants driving ability, those who took THC or the CBD/THC blend had scores comparable to a driver with a blood alcohol concentration of 0.05% – just below the legal limit in the U.S. and Canada.
However, the effects of THC use on driving ability subsided after approximately 4 hours, as drivers’ SDLP scores returned to placebo levels. This indicated that the mild driving impairment caused by THC is fairly short-lived.
“This is the first study to illustrate the lack of CBD effects on driving,” said study co-author Ian McGregor. “[It also provides] a clear indication of the duration of THC impairment.”
Possible Impact on International Drug-Driving Laws
While CBD has been legalized in both the U.S. and Canada, whether someone can be charged for impaired driving after using CBD products remain legally ambiguous.
In both countries, drivers may be subjected to a standard field sobriety test or other testing procedures if suspected of driving under the influence of alcohol or drugs.
“With cannabis laws changing globally, jurisdictions are grappling with the issue of cannabis-impaired driving,” Arkell said. “These results provide much-needed insights into the magnitude and duration of impairment caused by different types of cannabis.”
“[This] can help guide road-safety policy not just in Australia but around the world.”
Calvin Chan is a researcher and medical writer from Edmonton, Canada. As a big science nerd, he loves reading and writing about everything science - from cannabis to dark matter and even alien life. Calvin has a PhD from the University of Alberta.