CBD Doesn't Impair Driving, New Study Finds

As cannabis becomes legalized in different forms around the world, the public appetite for information about this psychoactive plant grows. Laws are changing rapidly across the U.S., but at the time of publication, cannabis is fully legal in 15 states and Washington D.C. People want to know how cannabis (also known as marijuana, among many other names) affects all aspects of life.

Previous studies have found mild impairment to driving ability in those using marijuana with high levels of tetrahydrocannabinol (THC), which is the chemical responsible for the drug's high sensation. But marijuana is made up of many different compounds, and another of them, cannabidiol (CBD), doesn't have the same effect on driving.

That's according to a new study, led by the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney and conducted at Maastricht University in the Netherlands, and published recently in the Journal of the American Medical Association (JAMA).

What's the Difference Between THC and CBD?

This is a crucial point. Both compounds interact with your body’s endocannabinoid system, but they have very different effects. "The most important difference is that THC is intoxicating (i.e. it gets you ‘stoned’), while CBD is non-intoxicating," explains Thomas Arkell, PhD, the lead author on the JAMA study.

THC and CBD also have slightly different pharmacological actions and can have different medical uses. "For example, CBD shows anticonvulsant effects which make it potentially useful in treating epilepsy, while THC can actually have proconvulsant effects," Arkell says. "In other situations, THC or a combination of THC and CBD may be more useful than CBD alone."

What Happened During the Study?

The researchers conducted a "real life" study by testing the participants (26 healthy men and women, of whom 22 completed the study) driving on a highway rather than with a driving simulator. The participants had an average age of 23, reported cannabis use less than twice a week in the last year but more than 10 times in their lives, and were not taking any medications known to affect driving.

At the start of each session, participants were given one of four preparations: 13.75 milligrams of THC, 13.75 milligrams of THC and CBD combined (in a 1:1 ratio), 13.75 milligrams of CBD, and a placebo. After vaping, participants did two hour-long driving tests on a highway near Maastricht: the first took place between 40 and 100 minutes after vaping, and the second occurred between the 240- and 300-minute benchmarks. Each driver's vehicle had a camera on the roof to monitor their performance, including lane-weaving. Participants completed four of these sessions, resulting in eight driving tests total.

Participants self-rated the effects of the preparation after each session, including their confidence in driving. Researchers also evaluated several measures, including memory, decision making, thinking skills, average speeds, and range of speeds. They also took blood samples from each participant to determine levels of cannabinoids.

Study Findings

The preparation of THC and the preparation of THC/CBD combined produced short-term impairment to driving, as measured 40 to 100 minutes into the session. The impairment was similar to that seen in drivers with a blood alcohol content of 0.05%. (To put this into context, a blood alcohol level of 0.08% when driving is a crime in all U.S. states apart from Utah, where the limit is 0.05%.)

However, the CBD preparation didn't affect thinking or driving skills compared with the placebo.

"These results provide the first real evidence that CBD does not produce driving or cognitive impairment," Arkell says. "This is really important information for patients using CBD products and for regulators who are grappling with issues around medical cannabis use and driving."

Arkell points out that it's important to recognize the limitations of the study. "We only looked at one CBD dose which we administered via vaporization," he says. "While we would expect to see similar results with higher doses of oral CBD, this is something that still needs further exploring."

"With rapidly changing attitudes towards medical and non-medical use of cannabis, driving under the influence of cannabis is emerging as an important and somewhat controversial public health issue," says Iain McGregor, professor of psychopharmacology, academic director of the Lambert Initiative for Cannabinoid Therapeutics, and co-author of the study.

More Research Is Needed

Professor McGregor also notes that the study was with occasional cannabis users. "We expect that impairment may actually be far less in regular users (e.g. medical cannabis users) due to tolerance," he says. "We therefore plan to repeat the driving study but with medical cannabis users and determine whether their driving is impaired at short intervals after use (as we saw with occasional users)."

When it comes to THC, things are more complicated. While more research is needed around the effects of cannabis in general, the intoxicating effects of THC should keep users off the road while it remains in their system. Additionally, because they are not regulated, some CBD products may actually contain THC along with other unknown ingredients, potentially causing unexpected impairment or other effects.