1 joint puts young drivers at heightened crash risk even 5 hours later: study

Young drivers are more at risk of a crash even five hours after inhaling cannabis, according to results of a recent clinical trial.

The research, conducted by Montreal's McGill University and funded by the Canadian Automobile Association, found driving performance declined significantly in key areas such as braking and reaction time, even that long after inhaling the equivalent of less than one typical joint.

"We're hoping that it gives people food for thought and that when they choose to consume cannabis, if they choose to consume cannabis, they make a safe plan to get home," said Erika Miller, a spokesperson for CAA Manitoba.

Driving performances, tested in a simulator at the Research Institute of the McGill University Health Centre, deteriorated as soon as participants were exposed to distractions common on the road, says the study published online Monday at CMAJ Open, an online sister journal to the Canadian Medical Association Journal.

The trial examined the impact of cannabis on the driving ability of recreational users (at least once in the past three months, but not more than four times per week), age 18 to 24. Participants were also tested with no cannabis in their system to set a baseline.

The testing was partly prompted by polling that suggests one in five young Canadians believe they are as good or better drivers stoned as they are sober, the CAA said.

"This new trial provides important Canadian evidence that cannabis can affect the skills needed to drive safely even five hours after consuming and underscores the idea that if you feel you're not safe to drive, you're correct," Miller said.

"We should treat cannabis the same way we treat alcohol. If you indulge, find another way home, like a designated driver, ride-share or transit, or stay where you are and don't drive for at least five hours afterwards."

The research tested participants' performance on four different days using the driving simulator and a useful field of view test.

Testing was randomized to occur at one hour, three hours and five hours after participants consumed cannabis.

A medical grade vaporizer was used to provide a dose of 100 milligrams of dried cannabis containing 13 per cent THC, the main psychoactive component in cannabis.

A typical joint is 300-500 mg of dried cannabis, the study's authors say.

The clinical trial research is a step toward more understanding of the effects of cannabis on driving, but governments must step up and provide more funding for additional basic research, Miller said.

"CAA is committed to working with stakeholders and doing our part to further the dialogue on this important road safety issue," she said.

CAA Manitoba has launched an educational social media campaign to deter cannabis-impaired driving, with an inter-provincial campaign to launch later in the year.