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Canadian study finds people 50 and older most likely to be driving high

Jan 14, 2022 | Media Partners, The GrowthOp

This post is presented by our media partner The Growth Op
View the original article here.

THC detected in twice as many injured drivers since the legalization of recreational weed.

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Drivers 50 and older were the injured group most likely to far exceed allowable THC levels while behind the wheel, Canadian researchers report in a new study that found more people overall seem to be driving high since recreational cannabis got the green light.

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When adult-use cannabis was legalized in October 2018, federal regulations spelled out the prohibited blood drug concentrations that would apply.

For THC and its related penalties, information from the federal government notes a straight summary conviction offence applies if THC per millilitre (ml) of blood is at or over 2 nanograms (ng), but less than 5 ng. The drug-alone hybrid offence applies if the THC per ml of blood is over 5 ng.

  1. Driving under the influence of cannabis can be a very risky behaviour, which is a grave public health concern.

    Cannabis-impaired driving: Here’s what we know about the risks of weed behind the wheel

  2. “There was no evidence of significant changes associated with cannabis legalization on post-legalization weekly counts of drivers’ traffic-injury ED visits.” / PHOTO BY ALEXLMX / ISTOCK / GETTY IMAGES PLUS

    Study: No spike in traffic-related injuries after Canada legalized recreational cannabis

  3. FILES: The Ottawa Police Service conducts MEGA Ride at Innes Road on Oct. 18, 2018. / PHOTO BY JAMES PARK /Postmedia

    Researchers say they’ve pinpointed how long THC is impairing, with smoking having shorter times than ingestion

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Published this week in the New England Journal of Medicine, researchers from the University of British Columbia (UBC) found that the largest increase in drivers exceeding 5 ng/ml were those 50-plus. “There were no significant changes in drivers testing positive for alcohol, either alone or in combination with THC,” according to a UBC statement.

Findings of the research team — headed by Dr. Jeffrey Brubacher, the principal investigator and an associate professor in UBC’s Department of Emergency Medicine — are based on an analysis of blood samples from 4,339 (3,550 before legalization and 789 after legalization) moderately injured drivers, when their condition warranted blood tests as part of clinical assessment.

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The patients received treatment at four B.C. trauma centres from 2013 to 2020, with investigators tracking THC levels greater than zero, at least 2 ng/ml and at least 5 ng/ml.

Over-legal threshold increase largest among older drivers, male drivers

The findings are not just about drivers 50 and older, researchers emphasize. Overall, “the prevalence of moderately injured drivers with a THC level of “at least 2 n/ml more than doubled,” with the increase being largest among older drivers and male drivers.

Specifically, 3.8 per cent of drivers had blood THC concentrations above the legal driving limit before legalization and 8.6 per cent after that.

Additionally, the proportion of drivers with more than 5 ng/ml THC increased from 1.1 per cent pre-legalization to 3.5 per cent post-legalization. “The largest increase was among drivers over the age of 50,” the statement adds.

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Investigators note the finding may signal that more people are choosing to get behind the wheel after consuming cannabis, the UBC reports.

The study was headed by Dr. Jeffrey Brubacher, the principal investigator and an associate professor in UBC’s Department of Emergency Medicine. /
The study was headed by Dr. Jeffrey Brubacher, the principal investigator and an associate professor in UBC’s Department of Emergency Medicine. / Photo by UBC

Despite the increased detection of THC, investigators say “there were no significant changes in drivers testing positive for alcohol, either alone or in combination with THC.”

THC concentration falls to under legal limit within four hours

Blood THC levels typically peak at over 100 ng/ml within 15 minutes of smoking cannabis and “drop rapidly to less than 2 ng/ml within four hours after smoking,” investigators say. For cannabis edibles, there is a similar drop after eight hours.

Citing the serious risks associated with using cannabis before getting behind the wheel, Dr. Brubacher says “it’s concerning that we’re seeing such a dramatic increase.” Findings “suggest more is needed to deter this dangerous behaviour in light of legalization,” he notes.

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Despite changes to the Criminal Code of Canada allowing for greater police power to test drivers for drugs — coupled with provinces and territories introducing new penalties — “the evidence shows that these new laws are not enough to stop everyone from driving after using cannabis,” he adds.

As such, the hope is that policymakers will take into account the findings “to design public information campaigns and enforcement measures that encourage drivers, especially older drivers, to separate cannabis use from driving,” says Dr. Brubacher.

Heightened accident risk above 5 ng/ml

A study published in 2019, for which Dr. Brubacher was also the principal investigator, showed little evidence of an increased accident risk when THC concentrations are below 5 ng/ml. Above that concentration, however, it was found that risk did rise.

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In a research article published last fall, U.S. researchers reported “issues such as detection procedures for cannabis-impaired drivers, and use of blood THC levels to gauge impairment, should rely heavily on current scientific knowledge.”

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An Australian study, also from last year, pointed out “many jurisdictions use per se limits to define cannabis-impaired driving.”

According to the Canadian Centre on Substance Use and Addiction,Per se laws provide a legal shortcut, essentially eliminating the requirement to prove the driver’s ability was impaired.”

Authors of the Australian study noted, however, that “there appears to be a poor and inconsistent relationship between magnitude of impairment and THC concentrations in biological samples, meaning that per se limits cannot reliably discriminate between impaired from unimpaired drivers.”

And a Canadian study from this past summer indicates neither Ontario nor Alberta witnessed a significant rise in emergency visits from traffic-related injuries since weed was green lit more than three years ago.

Emphasizing that detection does not necessarily equate to impairment, Dr. Brubacher, nonetheless, notes in the UBC statement that “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.”

Research team members are now expanding their investigation to 15 trauma centres across Canada.

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