October 22, 2018 by Greg Meckbach
A recent experiment in Montreal shows that people who smoked a small fraction of a joint were much riskier drivers than if they drove sober, the Canadian Automobile Association suggests.
CAA funded a study at the Research Institute of the McGill University Health Centre in which occasional users of cannabis did a series of practical tests using both a driving simulator and a computer.
For example, they were tested on their ability to brake quickly when a stop light turned red, to stay in their lane, to turn the steering wheel and to drive around an object that suddenly got into the path of the vehicle.
“When the task was more complex and something more novel, that’s when they made more errors” if they did the task within five hours of smoking cannabis, said Isabelle Gélinas, who co-authored the study, in an interview.
The study compared the performance of the same participants when they were sober and at intervals of one, three and five hours after using cannabis.
Possession of recreational cannabis was a criminal offence in Canada until Oct. 17 and for this reason, there “hasn’t been a lot of overt public education” on cannabis and driving, said Ian Jack, CAA’s managing director for communications and government relations.
“It’s simply been, ‘don’t do it, it’s illegal,’” Jack said. CAA funded the study because CAA officials are concerned about polls showing roughly one in five young people think cannabis does not impair driving.
“We wanted to address that myth that people are as good at driving stoned as they are sober. We are always interested in bringing information to the table rather than finger wagging.”
Young peoples’ understanding of cannabis and driving has been “passed on in conversations in school yards and at parties rather than being science-based, so that needs to change,” Jack said.
The results of the McGill study were published Oct. 15 in CMAJ Open, a sister publication of the Canadian Medical Association Journal.
With the computer study, the researchers tested participants’ ability to concentrate on two different things same time – such as driving when a passenger is speaking, Gélinas said in an interview.
“We didn’t have huge doses of cannabis that they were inhaling and they were still impaired,” Gélinas said.
Gélinas is a McGill University occupational therapy professor whose areas of research include the training of drivers who are seniors or who have disabilities.
Those who participated in the study did a series of practical tests using both a driving simulator and a computer. They used a medical grade vaporizer to consume a dose of 100 milligrams of dried cannabis.
There is three to five times that much cannabis in a “typical joint,” Gélinas said.
With some participants, even five hours after smoking cannabis, “they were still not safe to drive,” Gélinas said.
The results show that even more research needs to be done on cannabis impairment, Jack suggested.
“We do not claim this study is the definitive last word on this subject. We think it’s an important start to the conversation on the science of cannabis and driving,” Jack said in an interview.
The participants were occasional users between the ages of 18 and 24. The intent was to study the impact on driving ability in people who might smoke cannabis on occasion at a party – rather than regular users or people who use cannabis for medical reasons, Jack said.