A major B.C. study has found that a high proportion of young adults who consume marijuana admit they either drive while stoned or get into vehicles with drivers who’ve used marijuana.

Canadian studies have shown increased crash risks when drivers consume pot, and the high frequency of risky behaviour in the current study demonstrates a failure of approaches and the need for urgent action on the prevention and public-awareness front, the study says. This is especially relevant because of Canada’s plan to legalize recreational marijuana, according to lead author Bonnie Leadbeater, a University of Victoria psychology professor whose study is published in the journal Paediatrics and Child Health.

Vancouver General Hospital’s Jeff Brubacher, an emergency-room doctor and co-author of the current study, told Postmedia News recently that when marijuana is legalized, “there will be an increase in crashes, injuries and fatalities.”

The marijuana-use and driving-risks study by collaborators from the University of Victoria, University of B.C. and Vancouver Island Health is published in this Canadian journal.

Among frequent users of marijuana (more than once a week) in the study, 80 per cent of males and 75 per cent of females acknowledged they had, in the past month, been in a car driven by someone (including themselves) who had used marijuana or other drugs. Sixty-four per cent of frequent-using males and 33 per cent of females reported they were “intoxicated” with marijuana while driving, riding a motorcycle, boating or using machinery.

And half of the pot frequent-user males (42 per cent of females) said they’d been in a car with a driver who had used alcohol. Of occasional users (once a week at most), 28 per cent said they’d been in a car, in the past month, with a driver (including themselves) who had used alcohol.

“Epidemiological studies suggest that acute marijuana use approximately doubles the rate of crashing,” the study says, while allowing that the finding hasn’t been shown in all studies.

As Canada moves toward decriminalization, Leadbeater said governments must direct funding to education “that presents an accurate picture of potential harms.”

Research on marijuana and driving risks is critically important because youth are already vulnerable to not only being in crashes more than experienced drivers, but also more likely to be involved in fatal crashes as passengers. Consumption of marijuana exacerbates the risk for young drivers and their passengers, with or without concurrent use of alcohol, she said.

B.C. has the highest rate of marijuana use in Canada (13.8 per cent), according to Health Canada. In 2015, a study led by Brubacher found that just over seven per cent of injured drivers had consumed marijuana in the hours before the crash. The study of 1,100 drivers found that a greater proportion — 17.8 per cent of injured drivers — had consumed alcohol and of those, 15.8 per cent had illegal (over 0.08) blood-concentration levels.

A 2012 Canadian study showed that marijuana use peaks between ages 15 and 24, but Leadbeater said the risks of driving after consuming marijuana and other drugs never cease. In studies, pot use has been shown to slow reaction time, cause lane-weaving, distracted driving and affect the ability of drivers to maintain constant driving speed.

Leadbeater and her co-authors state that the fact that marijuana has become so ubiquitous leads to the ill-informed perspective that marijuana is innocuous.

“Today’s young drivers have witnessed legalization of medical marijuana, observed the proliferation of dispensaries or retail stores of marijuana products … and experienced the movement toward decriminalization. All of these social changes contribute to a view that marijuana use has few risks,” the study says.

It concludes: “The high frequency of driving-risk behaviours, particularly for frequent users, suggest that plans for legalization of recreational use should anticipate the costs of preventive education efforts that present an accurate picture of potential risks for driving.”

The study’s data is derived from interviews with over 600 participants in the Victoria Healthy Youth Survey, a longitudinal study launched several years ago. Study participants were 12 to 18 years old when it was first launched in 2003. They have been interviewed on a biannual basis up to 2013 and, for the latest secondary analysis, data pertaining to marijuana use and risky-driving behaviours involved about 500 participants ranged in age from 22 to 29.

Leadbeater and her co-authors said that while impaired driving law enforcement may pick up when recreational marijuana is legalized, “the capacity of police to detect and sanction marijuana use and driving through breathalyzers or biological tests linking consumption to impairment is limited.”

They suggest marijuana could come with packaging warning labels, and that more funding be directed to designated-driver campaigns and access to treatment for those who develop addictions.