Cannabis game changer: CBD safe for driving, THC effects fade in hours, landmark study finds

Cannabidiol (CBD) – a key component of medicinal cannabis products – does not impair driving, a landmark study led by Australian researchers has found.

CBD is one of 113 compounds identified in the cannabis plant and has a variety of medicinal uses, including the treatment of epilepsy, anxiety, chronic pain and addictions.

Published on Wednesday in the prestigious Journal of the American Medical Association, the study has the potential to influence the way cannabis is treated by legislators and law enforcement in Australia and around the world.

It also examined the effects of tetrahydrocannabinol (THC), the intoxicating component found in the cannabis plant.

Researchers found that a moderate amount of THC produces mild driving impairment, but the effects wear off after four hours.

The study is the first to show the lack of CBD effects on driving and to provide a clear indication of the duration of THC impairment. Photo: Maastricht University

The study was led by researchers from the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney and conducted at Maastricht University in the Netherlands.

The findings “indicate for the first time that CBD, when given without THC, does not affect a subject’s ability to drive”, lead author Thomas Arkell said.

That’s great news for those using or considering treatment using CBD-based products,” Dr Arkell said. 

With laws dealing with cannabis loosening in many places, governments are “grappling with the issue of cannabis-impaired driving”, he said.

Dr Thomas Arkell led the landmark study.

“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,” Dr Arkell said.

The study’s findings should allow for “evidence-based laws and regulation for people receiving medical cannabis,” he said.

How the study worked

The study was conducted in the Netherlands, where recreational and medicinal cannabis use is legal.

Participants vaporised cannabis containing either mainly THC, mainly CBD, THC and CBD in combination, or placebo cannabis (no active components).

The amount of THC vaporised by participants was enough to cause strong feelings of intoxication.

Participants then went for a 100-kilometre drive under controlled conditions on public highways both 40 minutes and four hours later.

Study participants were given cannabis containing different mixes of THC and CBD, then tested their driving abilities. Photo: Maastricht University

Cannabis containing mainly CBD did not impair driving, while cannabis containing THC or a THC/CBD mixture caused mild impairment measured at 40 minutes later but not after four hours, the study found.

Lambert Initiative academic director Iain McGregor said that “studying the effects of cannabis on driving with such precision in a real-world context is incredibly important”.

“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,” Professor McGregor said.

Previous studies have looked at the effects of cannabis on driving, but they have not “precisely quantified the duration of impairment” from THC, and most have overlooked CBD entirely.

“This is the first study to illustrate the lack of CBD effects on driving and to also provide a clear indication of the duration of THC impairment,” Professor McGregor said.

He said the results “should reassure people using CBD-only products that they are most likely safe to drive, while helping patients using THC-dominant products to understand the duration of impairment”.

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