Improvements needed to detect cannabis impairment among drivers, study finds

WINNIPEG — Substantial improvements are needed in Canada to detect cannabis impairment among drivers, according to a new review study recently published in the Canadian Medical Association Journal.

The improvements, the study says, are needed both to ensure public safety and protect the rights of legal cannabis users.

“We would love to have that one measure that says, okay, this person is impaired, or they aren’t, said Sarah Windle, one of the study’s lead authors. “But unfortunately, in the case of cannabis, it just isn’t that simple,”

Windle, now a Ph.D. student at McGill University, studied the issue with a team as a research associate at the Lady Davis Institute of the Jewish General Hospital in Montreal.

The study aimed to look at the issue of impaired driving and the legalization of recreational cannabis.

“We were really interested in trying to look and see if there was an association between legalization and increases in fatal motor vehicle collision,” said Windle. “The data weren’t there yet for Canada. So, we looked to the United States.”

Researchers found legalization in jurisdictions in the United States may be associated with a small yet significant increase in motor vehicle collisions and fatalities.

They extrapolated the data to the Canadian context and determined 308 additional driving fatalities could occur in this country each year.

“Whether this will actually play out in Canada is also another question,” said Windle. “There’s circumstances in Canada that are different from in the states which could prevent potential increases.”

“Canada legalizing on a national scale has allowed for some additional public health measures that the states just don’t have.”

But some of the shortfalls in Canada, according to the study, are with the current measures and tools used for detecting cannabis-impaired driving.

“We know that cannabis has an impact on driving,” said Windle. “Detecting cannabis, it doesn’t necessarily correspond directly to impairment. That’s a big, big challenge in this literature. At what level is somebody really impaired and it seems that varies on many factors: by (the) individual, by their level of tolerance, how often are they using, what kind of cannabis and its potency are they using.”

Changes to the Criminal Code in 2018 set out new laws and testing regimes for drug-impaired driving.

Police can use a Standardized Field Sobriety Test or a Drug Recognition Expert Evaluation to assess potential impairment but researchers say the validity of those tests remains uncertain.

In addition to those tests, police can now use oral drug fluid screeners to detect the presence of cannabis or other drugs, which may provide grounds for police to demand a blood sample.

For cannabis, drivers with a blood drug concentration of between 2 nanograms and 5 nanograms of THC per millilitre of blood can face a maximum fine of $1000.

Jeff Brubacher, an emergency physician and associate professor in the department of emergency medicine at the University of British Columbia, is studying the role of cannabis in motor vehicle collisions.

Brubacher also said detecting cannabis impairment is a complicated issue.

“The problem with the levels is that they don’t really correlate very well with impairment,” said Brubacher. “We researched the association between risk and levels and we found that people with levels less than five nanograms/ml were not at any increased risk of causing a collision.”

“That was interesting because the lowest per se limit is two nanograms/ml.”

According to a December 2020 Public Safety Canada report, the proportion of drug-impaired incidents has increased over the past 10-12 years, with cannabis being the most frequently detected drug among drivers. But the report found charges aren’t as common and convictions are less severe when compared to alcohol-impaired driving.

“There is a long-standing and continuing trend where charges are laid more frequently and lead to higher levels of convictions for alcohol than for drug-impaired driving cases,” the report concluded.

Chris Gamby, a lawyer and spokesperson for the Criminal Defence Lawyers Association of Manitoba, said this doesn’t mean drivers can break the law and get away with it.

“I don’t think that this should be interpreted as carte blanche to go and take recreational drugs and get behind the wheel,” said Gamby.

In an emailed statement, the Department of Justice said the federal government has invested $81 million to build capacity among frontline officers to enforce drug-impaired driving rules.

“These funds were allocated to, among other things, the provinces and territories to enhance the training of front-line officers and the purchase of the newly approved oral fluid drug screeners,” a portion of the statement reads. “Since 2018, the number of officers trained in SFST and the number of certifier DRE officers have doubled, and initial training has been rolled out on the new oral fluid screening devices. Furthermore, the number of drug-recognition evaluations conducted across the country has more than doubled since 2018.”

Windle said while more research needs to be done on detecting cannabis impairment, the current measures do come with potential consequences.

“If you exceed the legal limit, there are fines, there’s possible jail time for repeat offences and that is outside a determination of driving impairment.” 

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