Does cannabidiol in cannabis affect one’s ability to drive? It doesn't but THC does, claims analysis
In people who used a THC/CBD mixture, there was mild impairment during driving measured at 40 minutes later but not after four hours
Cannabidiol (CBD), a cannabis component used for many medical purposes, does not hinder the ability to drive, according to researchers. However, moderate amounts of the main intoxicating component tetrahydrocannabinol (THC) can produce mild driving impairment that lasts for up to four hours, they found.
The analysis involved people who inhaled vaporized cannabis containing different mixes of THC and CBD. They then went for a 100-kilometer 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, according to the report published in JAMA. It was led by the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney.
“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,” writes lead author Dr Thomas Arkell from the Lambert Initiative for Cannabinoid Therapeutics.
Medical treatment using cannabis-related products has grown: this includes increasing use of CBD-containing products for conditions such as epilepsy, anxiety, chronic pain, psychosis, neurological disorders, and addictions, say investigators. Many currently available products also contain a mixture of THC and CBD.
According to Dr Arkell, road safety is a primary concern and these results should allow for evidence-based laws and regulations for people receiving medical cannabis. “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,” he added.
What method did the researchers use?
The clinical trial was conducted at the faculty of psychology and neuroscience at Maastricht University in the Netherlands between May 20, 2019, and March 27, 2020. It involved giving 26 healthy participants (mean age: 23.2 years; 16 women) four different types of cannabis in a random order to vaporize on four separate occasions. Each participant’s driving performance was then assessed on the road in real-world conditions along a 100-kilometer stretch of a public highway in a dual control car with a driving instructor present.
The tests were done using an established scientific test that checks the standard deviation of vehicle position (SDLP), which is a measure of lane weaving, swerving, and overcorrecting. SDLP increases under the influence of alcohol and drugs such as Valium and Stilnox. Participants vaporized cannabis containing mainly THC, mainly CBD, THC, and CBD in combination, or placebo cannabis (no active components). The amount of THC vaporized by participants was enough to cause strong feelings of intoxication, says the team.
To test how the different types of cannabis affect driving, participants completed two one-hour, on-road highway driving tests starting at 40 minutes and at four hours after inhaling vaporized cannabis.
The study was conducted among healthy participants who were occasional cannabis users. Hence, the findings cannot be generalized. However, according to professor Iain McGregor, the academic director of the Lambert Initiative, 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 the impairment.
“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 the 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,” he concludes.