As access to legalized cannabis continues to expand throughout the world, many are wondering about how cannabis may affect those driving under its influence. Previous studies have found mild impairment to driving ability for those using cannabis with higher levels of THC (the chemical primarily responsible for cannabis’ characteristic high). But few studies have looked at whether CBD (another popular chemical in cannabis) impacts driving ability in similar ways.
CBD has grown increasingly popular in recent years, as an alternative to high THC cannabis. Those who use CBD say it offers many of the potential benefits of cannabis like lowering inflammation, reducing anxiety and easing pain. But unlike THC, it doesn’t leave those who take it feeling high or disoriented. CBD is also much more legally accessible than THC and can be easily ordered online. So given their high availability, it’s important for researchers to learn whether these products will adversely impact driving ability in those who take them.
Now, researchers have begun to investigate this question. A new study published this month in the Journal of the American Medical Association found no evidence that CBD causes impairment for drivers. The double-blind, randomized, clinical trial did find evidence of mild impairment for drivers using THC or a combination of THC and CBD. But those using CBD didn’t differ from those using a placebo when it came to driving ability.
This study, led by the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney and conducted at Maastricht University in the Netherlands, included 26 healthy occasional cannabis users. Participants were asked to vaporize one of three different cannabis options or a placebo. For those who took one of the cannabis options, they were given a 13.75mg dose of CBD, THC, or a combination of the two. Of course, since it was a double blind study, neither the participants nor those evaluating their driving knew who was under the influence of one of these substances and who had taken a placebo.
Once participants had used their vaporizers, the on-road driving tests began. Participants were given driving tests 40 minutes and 240 minutes after they consumed their cannabis (or placebo). They drove a special vehicle which could monitor their movements and they were also accompanied by a licensed driving instructor who could take control of the car if things became dangerous.
Those evaluating the driving abilities of participants were looking to measure lane weaving behavior – how well participants were able to stay in their lane as opposed to weaving into neighboring lanes. Known as standard deviation of lateral position or SDLP, this is a standard test for how substances impact driving. For example, those under the influence of alcohol tend to have higher SDLP than those driving sober.
The results of the test matched previous studies for those under the influence of THC. They showed that those using THC and those using a combination of THC and CBD had increased SDLP. For these occasional cannabis users, using cannabis with THC (even when CBD was also being used as well) led to mild impairments – comparable to someone with a 0.05% blood alcohol level. Those using THC also reported higher anxiety and reduced confidence in their own driving ability. Interestingly, those who used both THC and CBD had similar impairment to those who only used THC, but they felt less anxious and more confident to drive.
Still, these impairments didn’t last long. After 4 hours, no differences were detected between those who used the placebo and those who used THC. For those who used CBD, no statistically significant differences were found with SDLP at any point in time. In fact, SDLP was slightly lower for those on CBD than those who used a placebo.
This study adds evidence that vaporized CBD doesn’t impair driving ability, but it isn’t without its limitations. For one thing, CBD and THC dosing varies widely. While some available products have low doses like 5mg, clinical research on CBD has tested much higher dosing, such as 500mg doses. So a 13.75mg dose may be low compared to potential doses some cannabis consumers might be utilizing. It’s possible that with higher doses, we could see impairment from CBD, or increased impairment from THC.
This study was also limited to occasional cannabis users, so may not be reflective of how chronic or medical cannabis use impacts driving. Previous studies have found that daily cannabis users show less impairment when they are using cannabis than those who use cannabis only occasionally. So, it is important not to over generalize and assume daily cannabis users will face the same type of mild impairment from THC that we see in occasional users.
This study size was also fairly small, with only 26 participants, and they tended to be younger drivers. Results may also differ with a larger group of participants that includes a more diverse age range.