Unlike THC, the main psychoactive compound in cannabis that produces the “high” sensation, CBD does not appear to have the same effect on people.

However, only one previous study, also by researchers at the University of Sydney, directly investigated CBD’s effect on driving performance.

Researchers found that CBD did not increase how much people weaved or drifted in tests done on a driving simulator — a standardized measure of driving ability.

This earlier study used vaporized CBD-containing cannabis. CBD is more commonly ingested orally as oils, capsules, or edibles.

In the new small study, which was published May 30 in the Journal of Psychopharmacology, researchers gave 17 people CBD in oil — at one of three doses (15, 300, or 1,500 milligrams) or an inactive placebo.

Most studies on the beneficial effects of CBD use doses up to 1,500 milligrams.

Before and several times after taking CBD or placebo — up to 3.5 to 4 hours — participants completed tasks on a driving simulator.

This included following safely behind another car and driving along highways and rural roads. Researchers used these tests to measure how well people could control the simulated car.

Participants also took several computerized tests that measured their cognitive function, drug-induced impairment, and reaction time.

In addition, they reported on their subjective experience, such as whether they felt “stoned,” “sedated,” “alert,” “anxious,” or “sleepy.”

Each person completed the testing four times — for the three different doses plus the placebo — with at least seven days between each session.

None of the doses of CBD appeared to impair participants’ driving ability or cognitive performance or induce feelings of intoxication, the researchers found.

In addition, the average change in how much people weaved or drifted was smaller than what was seen with intoxication with other drugs in another study, the researchers said. It was also smaller than in the previous CBD and driving study.

“This is a well-done study that adds to an evolving literature that CBD alone is unlikely to be cognitively impairing or negatively affect driving performance,” said Dr. Marcotte, “although data on the latter remains sparse.”

In deciding whether CBD impaired drivers, researchers looked specifically at whether the impact of CBD was greater than what occurs at a 0.05 percent blood alcohol concentration (BAC).

In the measures they looked at, it was not.

Tim Brown, PhD, director of drugged driving research at the National Advanced Driving Simulator at the University of Iowa, said while BAC is a useful comparison, some driving impairment occurs at 0.05 percent.

And in some countries, this is the legal limit, whereas, in most U.S. states, it is higher — 0.08 percent.

“So not being worse than that level [0.05 percent] does not mean ‘safe,’” Dr. Brown said.

Researchers found that people who took 300 or 1,500 milligrams also reported lower levels of anxiety than those who took 15 milligrams of CBD or the placebo. This fits with other research looking at the anti-anxiety benefits of CBD.

Because of COVID-19 restrictions in place when the study was being carried out, researchers were unable to recruit as many people as they had originally intended.

As a result, they could not determine the impact of CBD on the “car following” part of the first simulated driving test, which occurred 45 to 75 minutes after people took CBD.

Brown said although the study suggests little effect of CBD on driving, the results should be viewed with caution.

Most of the participants were not frequent cannabis or CBD users, he said, so more research is needed to know whether long-term CBD use or CBD use alongside other medications affects driving ability.

Marcotte said future studies should also look at drivers taking CBD for medical or psychiatric symptoms, including older adults.

In addition, while the ability to stay in one’s lane when driving is a “good proxy measure of safety,” Brown said the results don’t rule out the impact of CBD on other aspects of driving.

“Drugs could have little effect or even improve lane keeping but still result in delayed reaction time to critical events,” he said.

For example, if a stimulant improves focus, a driver might be so intent on what’s happening before them that they miss — and delay responding to — what’s going on in their periphery, such as a child running into the road.

Brown said there are also signs that people in the study taking CBD may have driven slower, which can mask the effects of the drug on how much a person weaves or drifts.

Although the new study suggests that CBD is unlikely to impair driving through intoxication, some people taking CBD can experience drowsiness, which might affect their driving ability.

CBD can also potentially interact with other medications, including pain medications, antidepressants, seizure medications, and diabetes medications.

Drivers should also be careful about which CBD products they use because some may contain other cannabis components.

“In poorly regulated markets, it is important for users to be mindful that the purity of CBD products is not always clear, and THC (which can impair driving) may be present in some products,” Marcotte said.