TORONTO — With two months to go before recreational cannabis is legalized in Canada on Oct. 17, new data from the country’s national statistics agency is stoking fears about drugged driving and raising questions about the ability of law enforcement officials to detect impairment.

According to Statistics Canada data released last week, 1 in 7 cannabis users with a valid driver’s license has hopped behind the wheel within two hours of consuming the drug at least once within the past three months.

Other surveys from Health Canada and Public Safety Canada in 2017 also revealed that large percentages of Canadians are driving after consuming marijuana. In fact, 1 in 10 respondents of the latter survey said they believed cannabis makes a person “a more careful driver” – a conviction refuted by science.

But while Mothers Against Drunk Driving Canada described the Statistics Canada numbers as “alarming,” others say the survey data tells only part of the story since it does not indicate that those who drove after smoking were actually impaired.

Identifying marijuana impairment is a major issue that has beguiled Canadian lawmakers since the Liberal government of Prime Minister Justin Trudeau first introduced legislation to legalize the drug in April 2017.

Their attempt to do so is represented by Bill C-46, which overhauled Canada’s impaired driving laws. Under the legislation, drivers with two to five nanograms of tetrahydrocannabinol (THC) – the main psychoactive ingredient in cannabis – per milliliter of blood will face charges, which could result in hefty fines. Drivers exceeding the five-nanogram limit, or with both THC and alcohol in their systems, will face stiffer penalties, including up to 10 years in prison.


The problem, according to Rob De Luca, the director of the Canadian Civil Liberties Association’s public safety programs, is “that the link between THC levels and impairment is quite loose.”

Cannabis is unlike alcohol, which can be easily and accurately measured by a person’s blood alcohol content levels, experts say. Cannabis metabolizes differently, and factors ranging from body fat levels to personal history with the drug to how it was ingested affect whether a driver is impaired by it.

“Peak impairment does not occur when THC concentration in the blood is at or near peak levels,” a U.S. National Highway Traffic Safety Administration report to Congress in 2017 found. “In contrast to the situation with alcohol, someone can show little or no impairment at a THC level at which someone else may show a greater degree of impairment.”

An annex to Bill C-46 made the same point, noting, “the science is unable to provide general guidance to drivers about how much cannabis can be consumed before it is unsafe to drive or before the proposed levels would be exceeded.”

Habitual users of the drug and those who ingest it for medicinal purposes are likely to have high THC levels days or even weeks after they last consumed marijuana and long after experiencing its psychoactive effects, De Luca said. Some studies show that even people exposed to second-hand marijuana smoke can test positive for THC.

“There is a very real danger that someone who is not impaired will get caught up in the criminal justice system,” said De Luca, who anticipates Bill C-46 will face a barrage of legal challenges.


Justice Minister Jody Wilson-Raybould defended the rules earlier this year. “Until we have definitive scientific evidence around what is a safe level, we’re proceeding on a precautionary basis, saying there is no safe level,” she told the Globe and Mail.

Bill C-46 also grants police officers with reasonable suspicion that a driver is impaired new powers to administer roadside saliva tests, which determine whether a specific drug may be present in a driver’s system. The results are not admissible in court, but failing a test will spur arrest and further examinations at a police station.

Experts say that these tests and the devices used to carry them out are also riddled with problems. The NHTSA report found that “the accuracy and reliability of these devices has not yet been clearly established.”

A bill that would allow police in Vermont to use roadside saliva tests failed earlier this year because of these concerns.

Questions also have been raised about the ability of the devices, which require internal temperatures of at least 4 degrees Celsius (about 39 degrees Fahrenheit) to work, to function given Canada’s climate. A Public Safety Canada pilot study that tested some of these devices found that in 17 percent of cases where the device malfunctioned, temperature was responsible.

De Luca said the federal government should focus more on training drug-recognition experts – officers with specialized training to spot impaired drivers – than on THC limits.

Last month, the Canadian Association of Chiefs of Police said that it is unlikely to reach its goal of having 2,000 trained drug-recognition experts when cannabis becomes legal in October.

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