Better Measures Are Needed to Detect Cannabis Impairment While Driving, Experts Say

A study coming out of Canada proves what we all know—that more improvements are needed before we can truly understand cannabis impairment while driving, and before we can truly determine who is impaired. 

The study came from the Canadian Medical Association Journal and was conducted by a research team associated with Lady Davis Institute of the Jewish General Hospital in Montreal. Sarah Windle, who was a lead author on the study, is now a Ph.D. at McGill University. 

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

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

Through their research, the team dug into the US as well and discovered that legal areas in the states may be associated with significant increases in motor vehicle collisions and deaths. Put in the context of Canada, a country that has entirely legalized cannabis, they estimated that 308 additional fatalities from driving could occur due to legalization. 

“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.”

Problems With Determining Cannabis Impairment While Driving

However, this data was not entirely foolproof. According to the study, one of the biggest issues that remains is that there is not yet an accurate way to measure when someone is experiencing cannabis impairment while driving. Urine and blood tests report cannabis use from days before most recent consumption, and aren’t fair ways to tell if a driver is currently high. 

“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.”

Currently in Canada, police rely on a Standardized Field Sobriety Test or Drug Recognition Expert Evaluation to determine if someone has been using cannabis; however, the results aren’t always reliable. They can also rely on the outdated methods of urine or blood samples. 

According to Jeff Brubacher, an emergency service doctor and professor at University of British Columbia teaching about emergency medicine, the issue of determining just how much cannabis plays a role in impairment is a complex one. 

“The problem with the levels is that they don’t really correlate very well with impairment,” said Brubacher regarding the inconsistency of data available on this issue. “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.”

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

There is no clear answer as of yet as to how we should determine cannabis impairment while driving, and more work needs to be done to determine this answer. But research like this helps provide more data and gets the legal cannabis world one step closer to solving the problem of impaired driving.