‘Very large increase’ in weed-related traffic injuries since legalization: study

Over a span of 11 years, annual rates of Ontario emergency department visits for cannabis-related traffic injuries surged dramatically, according to a recent study from The Ottawa Hospital.

The study, published Wednesday in JAMA Network Open, looked at cannabis involvement in emergency room visits for traffic injuries between 2010 and 2021 in Ontario. It also examined shifts in cannabis consumption and driving habits following federal legalization in 2018.

“Our data is raising concern about a growing problem of cannabis impairment and severe road injuries,” said lead author, Dr. Daniel Myran, who is also a fellow at the Bruyère Research Institute and with the University of Ottawa’s Department of Family Medicine.

“Since 2010 there has been a very, very large increase in cannabis involvement and traffic injury visits in Ontario.”

The study also found sharper spikes of marijuana involvement in traffic-injury emergency visits following legalization, he added.

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On Oct. 17, 2018, marijuana was legalized in Canada. A 2020 Statistics Canada report found that the legalization of cannabis was associated with an increase in overall consumption, especially among people aged 25 and older. And with legalization came amendments to impaired driving laws in the country, adding limits on blood tetrahydrocannabinol (THC) levels.

This is because cannabis can impair the cognitive and motor abilities necessary to operate a vehicle and doubles the risk of crash involvement, according to the Canadian Centre on Substance Use and Addiction.

With the rise in cannabis use over the years, Myran and his research team wanted to find out if there were shifts in cannabis-impaired driving.

“Going into legalization, one of the major public health concerns was that you might see an increase in cannabis-impaired driving and problems with road safety,” Myran told Global News.

“There’s a pretty large body of evidence showing that cannabis use impairs people’s driving performance, but it’s much less of a clear question of what happens when you change the regulations of cannabis on driving safety.”

Since 2010, the rate of total traffic injury emergency room visits that involved cannabis increased by 475.3 per cent, according to the study.

During this same time period, the researchers found the rate of total traffic injury emergency room visits that involved alcohol increased by 9.4 per cent. 

To find this data, the researchers examined medical record data of emergency room visits for traffic injuries in Ontario (motor vehicles, pedestrians and cyclists). It included records from January 2010 and December 2021.

The researchers then looked for documented cases of cannabis involvement.

“So someone is in emerge, they’ve had a traffic injury, and the treating team felt that cannabis use contributed to that traffic injury” Myran explained.

Out of the 947 ,604 traffic injury emergency room visits, 426 had documented cannabis involvement, the study found. The data did now specify what time of cannabis strain was detected.

Following legalization (October 2018 to March 2020), which came with limited retail stores and cannabis product options, the study found a 94-per cent increase in the quarterly rate of cannabis involvement in traffic injury emergency room visits.

And after legalization (April 2020 to December 2021), with more retail stores and expanded products, the researchers witnessed a greater increase of 223 per cent in rates. This period also overlapped with the COVID-19 pandemic.

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“Cannabis-involved traffic injury visits were increasing pre-legalization, and the period of market commercialization may have resulted in further increases in such visits,” the authors stated in the study.

The study also found that younger adults, particularly males, had an “increased risk of cannabis-involved traffic injuries.”

Almost half of the cannabis-involved traffic injury emergency visits also had alcohol involvement, the study found.

In terms of the nature of the injuries, Myran characterized them as “severe.”

“Individuals who had documented cannabis involvement in a traffic injury (emergency room) visit, 49.5 per cent of them are admitted to the hospital and 21 per cent of them are admitted to the intensive care unit,” he said.

“And in comparison, only six per cent of people who’ve had a general traffic injury visit go to hospital and only 1.8 per cent go to the ICU. So we’re talking 20 times more likely to be admitted to the intensive care unit.”

While the study focuses on Ontario, Myran believes that similar changes have likely occurred nationwide.

“More and more Canadians have been using cannabis over the past 10, 15 years, and with more people using cannabis, there’s more potential for cannabis-impaired driving,” he said.

Although research in this area is currently limited, he said he hopes for more comprehensive studies in the future to better address and prevent cannabis-related impaired driving.

Steve Brown, a research associate with the Traffic Injury Research Foundation (TIRF), said the organization has seen a rise in of traffic collision deaths linked to cannabis use over the years.

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TIRF’s national fatality data shows that from January 2016 to October 2018, 21.5 per cent of drivers killed in collisions in Canada tested positive for cannabis use, he said. However, from October 2018 to the end of 2020, this figure rose to 26.4 percent, according to Brown.

“Another consideration is that most drivers that test positive for cannabis — among the drivers that are killed — most of them had also been consuming alcohol,” he said.

“It’s not strictly an Ontario problem,” he added.

“The percentage of drivers testing positive for cannabis has increased post-October 2018, in some provinces at a modest rate, in some provinces the increase was a little more pronounced.”