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The effects of CBD and THC on driving – study

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Vehicle used to test cannabis impact on driving. Credit: Maastricht University

Research shows cannabidiol is safe for driving and the effects of THC fade in hours.

A landmark study on how cannabis affects driving ability has shown that CBD does not impair driving, while moderate amounts of the main intoxicating component THC produce mild driving impairment lasting up to four hours.

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

Lead author Dr Thomas Arkell said: “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.”

There has been substantial growth in medical treatment using cannabis-related products in Australia and overseas. This includes increasing use of CBD-containing products for conditions such as epilepsy, anxiety, chronic pain and addictions. 

Many currently available products also contain a mixture of THC and CBD.

The research involved people inhaling vaporised cannabis containing different mixes of THC and CBD, then going for a 100-kilometre drive under controlled conditions on public highways both 40 minutes and four hours later. 

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.

Dr Arkell said: “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”.

“Road safety is a primary concern,” Dr Arkell added.

“These results should allow for evidence-based laws and regulation for people receiving medical cannabis.”

The study involved giving 26 healthy participants four different types of cannabis in a random order to vaporise on four separate occasions. 

Each participant’s driving performance was then assessed on the road in real-world conditions along a 100-kilometre stretch of public highway in a dual control car with a driving instructor present.

 

The Academic Director of the Lambert Initiative, Professor Iain McGregor, said: “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.

“While some previous studies have looked at the effects of cannabis on driving, most have focused on smoked cannabis containing only THC (not CBD) and have not precisely quantified the duration of impairment.

“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.”

Participants vaporised cannabis containing 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.

To test how the different types of cannabis affect driving, participants completed two one-hour, on-road highway driving tests commencing at 40 minutes and at four hours after inhaling vaporised cannabis.

Prof McGregror added: “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.”

Sarah Sinclair is an award-winning freelance journalist covering health, drug policy and social affairs. She is one of the few UK reporters specialising in medical cannabis policy and as the former editor of Cannabis Health has covered developments in the European cannabis sector extensively, with a focus on patients and consumers. She continues to report on cannabis-related health and policy for Forbes, Cannabis Health and Business of Cannabis and has written for The i Paper, Byline Times, The Lead, Positive News, Leafie & others. Sarah has an NCTJ accreditation and an MA in Journalism from the University of Sunderland and has completed additional specialist training through the Medical Cannabis Clinicians Society in the UK. She has spoken at leading industry events such as Cannabis Europa.

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