More people in B.C. driving while high since legalization: study
Cannabis is being detected in twice as many injured drivers since it was legalized says the findings of a University of British Columbia study.
The UBC study showed that the amount of cannabis in a driver's blood following an injury has more than doubled since legalization.
The study published Thursday, Jan. 13, in the New England Journal of Medicine says the findings may be a signal that more Canadians are choosing to drive after using cannabis.
"It’s concerning that we’re seeing such a dramatic increase," UBC department of emergency medicine associate professor Dr. Jeffrey Brubacher said in a media release. "There are serious risks associated with driving after cannabis use. Our findings suggest more is needed to deter this dangerous behaviour in light of legalization."
Dr. Brubacher, who was the principal investigator of the study, looked at blood samples from 4,339 moderately injured drivers who were treated at four B.C. trauma centres between 2013 and 2020.
The study found that before legalization 3.8 per cent of drivers had blood tetrahydrocannabinol, or THC as its more commonly known, concentrations above the Canadian legal driving limit of 2 nanograms/ml.
However, after legalization that number rose to 8.6 per cent.
THC is the main psychoactive compound in marijuana.
The number of drivers with high levels of THC in their blood increased threefold from 1.1 per cent pre-legalization to 3.5 per cent afterwards.
The UBC study found the largest increase was in drivers over the age of 50.
There was no significant change in drivers testing positive for alcohol, either alone or in combination with THC.
The study points out that after cannabis legalization the Canadian government changed the law to give police more power to test drivers they suspected had consumed drugs.
"The evidence shows that these new laws are not enough to stop everyone from driving after using cannabis," Dr. Brubacher said. "We hope that policymakers will use our findings to design public information campaigns and enforcement measures that encourage drivers, especially older drivers, to separate cannabis use from driving. At the same time, it is important not to lose sight of alcohol-impaired driving, which is extremely high risk, especially when combined with cannabis."
The report says that after smoking cannabis blood levels of THC normally peak at around 100 nanograms/ml, before reducing to two nanograms/ml after four hours.
After eating cannabis the levels take around eight hours to drop the same amount.
"While cannabis use is associated with cognitive deficits and psychomotor impairment, Dr. Brubacher cautions that the presence of THC in the blood is not always an indicator that a collision was caused by cannabis impairment," the release says.
A previous study showed that there was little evidence that THC concentrations below five nanograms/ml increased the risk of motor vehicle accidents.
However, levels higher than five nanograms/ml did increase the risk of car crashes.
"Detecting cannabis, especially at low concentrations, doesn’t necessarily mean a driver is impaired," Dr. Brubacher said. "But the risk is real with higher THC levels, which is why it’s so important that we continue to assess and respond to the impact that legalization is having on road safety."
Dr. Brubacher is now expanding his research to 15 trauma centres across Canada and looking at the prevalence of cannabis, alcohol and other impairing substances in injured drivers.
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