Opponents of cannabis legalization often cite the drug's ability to impair driving and contribute to car crashes. Indeed, cannabis is the second most common drug found in under-the-influence drivers after alcohol.
But a study from University of Sydney researchers, published today in the Journal of the American Medical Association, found people who vaped cannabis that contained only CBD, a non-psychoactive component of the drug, could drive just as well as those who didn't consume anything.
They also found that people who vaped cannabis containing 9% CBD and less than 1% THC, a psychoactive component that can cause slowed reactions and warp the perception of time, were less likely to sway a car off-path than people who vaped THC-only cannabis before driving.
These findings could benefit people who use CBD products for pain, epilepsy, and anxiety on a regular basis, according to researchers behind the 26-person study.
"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," Iain McGregor, academic director of the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney, said in a press release.
To study how different types of cannabis affected participants' driving skills, the researchers focused on how much they veered from a straight path while driving, using a measurement called standard deviation of lateral position (SDLP).
They randomly assigned study participants to vape a placebo, high-THC cannabis, high-CBD cannabis, or cannabis that contained equal parts CBD and THC.
Researchers asked each person to rate how high they felt. They also rated their levels of anxiety, sedation, confidence, and enjoyment of the drug effect on 10-point scales.
40 minutes later, participants drove on a 60 mile-long public highway at 60 miles per hour while in-car cameras recorded their behavior. They drove the same route four hours later and were asked to rate how they thought they did following each hour-long drive.
After the experiment, researchers found that participants who only vaped CBD were able to control the car and prevent swerving just as well as those who took the placebo.
Those who took THC and CBD together, plus those who vaped just THC, were more likely to veer off route during the first driving test, but not at the second test four hours after consuming THC-containing cannabis.
The researchers also found that THC-related car-veering was about the same as that in drivers with 0.05% blood alcohol content after drinking, the equivalent of at least four alcoholic beverages in two hours for a 170-pound man.
"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," Arkell said in a press release.
The study did have limitations. The small number of participants, all of whom were healthy, between ages 20 and 50, and reported cannabis use up to twice weekly, only represent a subset of the population. That means the findings can't be generalized for those who don't use cannabis regularly or have underlying medical conditions.
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