Consuming cannabis before getting behind the wheel is never a good idea, but just how much influence does it have on our driving?

A study published on Tuesday suggests that low doses of CBD don’t have an influence on people’s capabilities to drive. It also found that while THC is capable of impairing drivers, the effects wear off within a period of four hours.

The study, published in the Journal of the American Medical Association, is the first to analyze the impact CBD has on driving, while also providing more information as to how THC affects us behind the wheel.

“These findings indicate for the first time that CBD, when given without THC, does not affect a subject’s ability to drive. That’s great news for those using or considering treatment using CBD-based products,” said the study’s lead author Dr. Thomas Arkell.

Photo by William Krause via Unsplash

Researchers examined 26 healthy adults who were given four different types of inhaled vaporized cannabis at random. The cannabis administered was made up of different mixes of THC, CBD and placebo cannabis, with no active components. These volunteers were then asked to go on a drive for about an hour in a public highway, under controlled but realistic conditions, driving a dual control car alongside a driving instructor. Participants had to go on two separate drives, one done after 40 minutes of having consumed and the other four hours after consumption.

Results revealed that subjects who consumed strains comprised of pure CBD were not impaired at any time while driving. Subjects who consumed strains made up of CBD and THC or pure THC, however, experienced mild impairment on their first drive, 40 minutes after consuming it. When these subjects went on their second drive, four hours after consumption, there was no noticeable impairment.

“With cannabis laws changing globally, jurisdictions are grappling with the issue of cannabis-impaired driving. 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,” said Dr. Arkell.

Driving while under the influence of THC has been a much discussed topic, especially now as more and more states legalize its recreational use. Industry manufacturers are working on devices capable of measuring THC intoxication, but the technology isn’t there yet. In the meantime, more information and studies are needed in order to learn about the subject, to correctly measure the amount of THC that’s in person and to provide guidance in how to handle them if they’re caught driving.