A six-year study involving over 10,000 Canadian drivers in motor vehicle collisions indicates that cannabis has overtaken alcohol as the most frequently detected impairing substance in post-crash blood tests.
The National Drug Driving Study 2024, conducted by the University of British Columbia, analyzed blood samples from drivers across British Columbia, Alberta, Saskatchewan, Ontario, Quebec, Nova Scotia, New Brunswick, and Newfoundland and Labrador from 2018 to 2023.
The findings revealed that 54 percent of these injured drivers tested positive for at least one impairing substance. Among them, 16.6 percent had cannabis in their bloodstream, while 16 percent had alcohol.
“Driving after cannabis use appears to be an emerging problem in Canada and may now be more common than driving after drinking alcohol,” the study states. It emphasizes, however, that the higher crash risk associated with alcohol and the generally low THC levels in ‘cannabis positive’ drivers suggest that alcohol remains a more significant issue.
Atlantic Canada showed the highest proportion of injured drivers testing positive for cannabis. Out of 624 drivers from Nova Scotia, New Brunswick, and Newfoundland and Labrador, 26 percent tested positive for cannabis, compared to 22 percent for alcohol. Overall, 70 percent tested positive for drugs or alcohol, exceeding the national average.
Lead author Dr. Jeff Brubacher from UBC’s department of emergency medicine highlighted the notably high prevalence of impaired driving in Atlantic Canada. “That was the single most striking thing,” he noted, adding that while impaired driving is a nationwide issue, it appears more pronounced in Atlantic Canada.
Brubacher explained that the presence of cannabis in drivers has increased since its legalization in 2018. Despite this, alcohol remains the primary concern. “Good old-fashioned alcohol is still probably the biggest problem of a single substance,” he said, but noted the growing concern over the combination of alcohol and cannabis, which poses a significant risk.
The study outlines that cannabis intoxication can cause attention deficits, slow reaction times, and impair tasks such as lane tracking and speed monitoring. However, habitual cannabis users might develop some tolerance to its effects.
“The effect of alcohol on driving and road safety is well-studied and understood,” the study says. “Unlike alcohol, it is often not possible to predict how driving will be affected at different drug-blood-alcohol concentrations.”
Brubacher emphasized the importance of the study for emergency room physicians, public health officials, police, and organizations promoting safe driving. “It’s just to warn people of the risks of driving while impaired, of the risks of combining alcohol and cannabis,” he said. He expressed hope that ongoing data collection would aid police enforcement and public education efforts in reducing impaired driving incidents.
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