Is it safe to drive on CBD? Scientists are worried about 1 side effect

The world of CBD is expanding. Now that it comes in special edition Carls Jr. Burgers, gummies, seltzers, and sports products, evangelists behind the now-famous cannabinoid are finding uses for it in almost any situation: from post-workout relaxation to a mid-afternoon productivity jolt. Meanwhile, the Food and Drug Administration (FDA) has hinted that there are some places that CBD's effects may not translate well — starting with behind the wheel of your car, even if it can't even get you high.

Tetrahydrocannabinol (THC) is the chemical that's responsible for marijuana's characteristic high. Though cannabidiol (CBD) is also an active ingredient of cannabis, its effects on the brain and body are far different, raging from anti-epileptic qualities to potential anti-anxiety effects.

It's increasingly obvious that THC and driving don't mix: A 2018 research letter published in Jama Internal Medicine revealed that "holiday" 4/20 was linked to a 12 percent increase in fatal car crashes (though that study wasn't able to control for potential alcohol use). But even among sober drivers, a January 2020 study linked chronic THC use to impaired driving skills — especially in teens who started smoking weed before the age of 16.

How CBD affects driving though, is more of an open question, going by a press release issued by the FDA in December 2019, aimed at weary holiday travelers. The agency cautioned that drivers should "use caution if planning on operating a motor vehicle after consuming any CBD products." That warning was based on the assertion that CBD can cause drowsiness, sedation, or lethargy, the release states.

There are, for now, very few studies investigating how CBD may impact driving. However, Thomas Arkwell, a Ph.D. candidate at the University of Sydney, did investigate the relationship between CBD, THC, and driving in a 2019 paper published in the journal Psychopharmacology. He tells Inverse that CBD use is unlikely to impair driving, but scientists are still examining its effects, because "we don't know for sure."

"There is some evidence to suggests that CBD may cause mild sedation at high doses, and this could translate into subtle driving impairment," Arkell says.

The science of drowsy driving

The concern over CBD's effects on driving performance has little to do with its status as a cannabinoid. Instead, the concern links back to the extract's proposed mild sedative effect. That effect has anecdotal backing (about 10 percent of Americans who reported trying CBD used it to try to improve sleep, a 2019 Consumer Reports survey notes). That sedative effect is also noted in several previous studies — but, Arkell notes, those were only documented when it was taken in high doses.

In contrast to the sparse research on CBD and driving, the research on well-known drowsy drugs, like sleep aids, and their effects on driving performance are clear. Take one 2015 review published in The American Journal of Public Health. That study analyzed the collision records of 404,171 adults who reported using trazodone (an anti-depressant), temazepam (a prescription sleep-aid) and zolpidem (usually sold as Ambien). The use of any of those three drugs increased the chances of a car accident, but the results were particularly striking for Ambien users.

Ambien-users risk of accident doubled compared to people who didn't use the drug. The authors likened the impairment to having a blood alcohol level of between .06% and .11% percent — close to or over the legal limit to drive.

That said, there are big differences between a drug like Ambien, which is intended to knock you out at night and CBD, where the sedative effects, if seen at all, are often described as mild. Still, even non-drug induced drowsy driving is a major concern for regulatory agencies like the CDC.

The National Highway Traffic Association notes that 795 people died as a result of drowsy driving during 2017, and the CDC estimates that lack of sleep and driving alone was responsible for 72,000 injuries in 2013.

"We will have the answer to this very soon!"

Even a minor connection between CBD and drowsiness, says Arkell, is enough to justify looking into whether CBD might be on thing that makes you just a little bit less alert while on the road. That's the direction his research is currently taking, though there's not a clear answer yet.

"We are also nearing the end of an on-road driving study which is looking at the effects of THC and CBD, both alone and in combination, on real-world driving performance," Arkell says. "So we will have the answer to this very soon!"

Myths about CBD and driving

If they exist, CBD's effects on driving are likely subtle. Still, Arkell explains that one major myth about CBD and driving endures: the idea that CBD can actually counteract THC's known negative effects. It's true that research suggests that CBD can help offset the anxiety-inducing effects of THC. But Arkell is concerned that this research may be being mistranslated.

"There is a lot of misinformation on the internet about how CBD can modulate the effects of THC, and I worry that this information might be passed on to unsuspecting medical cannabis patients and consumers," he says.

"There is a lot of misinformation on the internet about how CBD can modulate the effects of THC."

Luckily, Arkell's research, which involved a simulated driving test and some THC and CBD-laced vapes, provides some clarification.

In his study, 14 participants vaped 125 milligrams of liquid that was either THC-heavy or equal parts CBD and THC. Then, each participant played a simulated driving game where they had to follow GPS instructions on highway or rural roads. When participants vaped both THC and CBD in equal concentrations, they tended to swerve more during their driving tests and reported feeling impaired up to four hours later.

"Our research suggests that CBD does not reduce the impairing effects of THC, at least with respect to driving, so it’s important that people are aware of this and can make their own decisions accordingly," Arkell adds.

Importantly, this study didn't include a CBD-only condition, which the authors say was because vaping CBD alone is "uncommon in the real world" (though this is likely changing). However, the team did find that when CBD and THC were administered in equal doses there were higher traces of THC in the participant's blood compared to when they got THC alone, suggesting that the interplay between CBD, THC, and driving could be of concern going forward.

Still, the kind of CBD that we might ingest and think nothing about — like seltzer or a gummy — probably doesn't help your performance on the road (especially if you're already impaired). As far as the consequences of CBD use and driving go, if they're out there, ongoing work is looking to illuminate them.

In the meantime, if you're worried about being drowsy on the road, a good night's sleep is probably the best place to start.