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How High Is Too High to Drive?

More young Canadians are driving stoned than drunk, but research is limited on how dangerous it really is.

Photo via Flickr user Ethan

This article originally appeared on VICE Canada.

Within a few minutes of strapping into the mock Chevrolet being used to test the effects of driving stoned at Toronto's Centre for Addiction and Mental Health (CAMH), I had swerved violently twice and nearly killed a jaywalker. And I wasn't even high.

Called the Virage VS500M, the sophisticated driving simulator includes a cabin with a driver's seat, steering wheel, brakes, and acceleration, and three 52-inch LCD displays to provide a view of the road and surroundings. It's been used to train student drivers and people in rehabilitation, but participants in the CAMH study are trying it out "medicated" to see how well they perform.


So far, about 100 people aged 19–25 have had their driving abilities recorded before and after smoking a joint containing either THC or a placebo. Blood samples taken at the time let scientists know how high they are.

"We can measure how well you respond to challenges, like what do you do when somebody jumps out in front of the road," lead researcher Dr. Robert Mann told VICE. (I, apparently, scream and clip them.)

The study is double blinded, meaning nobody, including researchers, know who is high and who isn't.

But early findings show test subjects who've smoked cannabis have trouble under "divided attention conditions," e.g. when they're asked to count backward by threes while driving, something that's arguably a lot simpler than remembering to check your blind spots or how to parallel park.

"It makes the driving task more complex," said Mann.

While there's tons of research on the impacts of drinking and driving, much less has been said about driving stoned, and for many people, the latter isn't taboo.

Almost without exception, every friend who learned I was doing this story responded with, "I've done that. It's not that bad," or, "I just drive slower." Mann said because of people's tendencies to drive slower when baked, there's a misconception that they're being safer than usual.

But with legalization in Canada pending, there's been a push from substance abuse experts and law enforcement to get more information on the potential dangers of cannabis impairment, including slower reaction times, shortened attention spans, and a hindered ability to accurately judge time and distances. Colorado and Washington, both of which have legalized recreational weed, have seen increases in both the number of fatal car accidents and the percentage of drivers involved in those crashes who tested positive for cannabis, though a definitive link has not been made.


While just five percent of Ontario students reported drinking and driving in 2015, according to a CAMH survey, 10 percent said they drive under the influence of cannabis. A survey by the Partnership for a Drug-Free Canada revealed 32 percent of teens didn't consider driving stoned to be as bad as driving drunk, and about 25 percent of parents of teenagers agreed.

Data looking at the impact of cannabis on collisions, however, indicates there's a real risk. One meta-analysis published by Dalhousie University in 2012 said stoned drivers nearly double their chances of being in a crash.

But cannabis impairment in drivers is harder to detect than alcohol, and therefore more difficult to set restrictions around. In Canada, if cops suspect you're driving stoned, a drug recognition expert, of which there are currently 600 in the country, might be called in to issue a standardized field sobriety test. The tests are comprised of simple tasks, like asking someone to walk a short distance and turn around.

Those who are stoned sometimes "forget what the instructions were—they can't concentrate," said Superintendent Paul Johnston, an Ottawa police officer who is on the drug abuse committee of the Canadian Association of Chiefs of Police.

Johnston told VICE police are expecting a spike in cannabis-impaired driving once legalization kicks in. He's adamant that it's just as bad as drinking and driving ("it's not only physical, it's cognitive"), and says a strong education-based framework needs to be in place before the laws change.


As of this minute, there's no breathalyzer equivalent police can use to tell how high a driver might be. But Johnston said police are testing out three different oral fluid testers, which use saliva to answer that question. Canada is also lacking a per se law—a THC-blood level (similar to a blood-alcohol limit) over which it would be illegal to drive. In Washington, the limit is five nanograms per milliliter of blood.

Part of the problem with weed is people don't know how much THC they're consuming in any given product, Johnston said, adding we need to study how long it takes for cannabis to dissolve in the system—i.e. how long after consumption before it's safe to drive.

"If you've smoked marijuana you could get anywhere from three to seventeen percent [THC]. If you smoke dabs, the concentration could be eighty, ninety percent."

Due to (unfortunate) "ethical reasons," I wasn't allowed to drive the mock Chevy high. While I found it to be pretty realistic—the seat actually vibrates—I also felt nauseous while driving and afterward, apparently a common side-effect.

Asked how that might impact the results, Mann said "at first it seems different or perhaps more difficult, but after a while, you get used to it. There is a lot of research now that validates simulator measures as strong predictors of driving performance."

The testing phase of the study will be wrapping up shortly, Mann said, with findings to be published thereafter.

Johnston told VICE that Canadians are well aware of the dangers of drinking and driving, but when it comes to cannabis impairment, "we haven't done as good a job of explaining the risks."

Research, training of police officers, technology, and awareness campaigns should make up a part of the government's plan for legalization, he said.

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