Research team explores risks of driving while stoned

A sobering debate could be one step closer to resolution, thanks to a University of Victoria professor and a research team that aims to measure how being high affects a person’s ability to drive.

Dr. Scott Macdonald is investigating how pot impairs.

A sobering debate could be one step closer to resolution, thanks to a University of Victoria professor and a research team that aims to measure how being high affects a person’s ability to drive.

While it may sound like common sense, Canada has never performed a comprehensive study to conclude that THC, the active ingredient in marijuana, impairs driving skills.

A similar study was conducted by an Australian researcher for fatally-injured drivers, which found those with active THC in their blood were significantly more likely to be responsible for their crashes. However, B.C.’s multicentre culpability study will be a first of its kind in Canada. The research team will work with five hospitals throughout the province to utilize blood sampling, the most accurate form of THC detection.

“We know from lab studies that cannabis impairs performance, but we know people also drive with real-world conditions and this study looks at the risks actually involved with that impairment,” says Dr. Scott Macdonald, a professor and scientist out of UVic, and the assistant director for the Centre of Addictions Research. “To date, this will be the most methodologically sound study done of its kind in the world.”

The researchers hope to study more than 3,000 subjects over a period of five years and will utilize a portion of the blood samples taken from people in accidents who already had to consent to blood work. This, Macdonald says, is the only way to ensure no bias in lab results, since many people — even a control group — would not voluntarily submit to something as invasive as blood sampling. However, as opposed to urine, saliva or hair samples, which can indicate the presence of THC days or months ago, a blood test remains the most accurate way to register the exact THC levels at the time of a crash.

“I feel good about this study; we see a lot of research attempted on cannabis, but there are so many flaws in the methodology that we’re just getting conflicting information,” says Macdonald. “There is a lot of mythology out there about the risks of driving impaired.”

In addition to Macdonald, who has spent the last 25 years researching the epidemiology of drugs and impairment, the team includes emergency care physicians from Vancouver, University of British Columbia scientists and the researcher who headed the Australian study. A pilot project, which involved over 100 subjects, was recently completed and used to help secure funding for this million-dollar study.

The team will be examining four different control groups, ranging from a level of 1, with little or no THC in the blood, to over 3.5, which indicates a level of severe intoxication. While it’s hard to compare between the two, Macdonald suggests that a THC level of 3.5 could be equivalent to a blood-alcohol level of 0.1 — significantly over the limit.

Currently, in B.C., the legal blood alcohol limit is 0.05, with anything above 0.08 falling into the criminal category. While many people round that off to a grey safety zone of about one drink per hour, it’s more challenging to know how many puffs would do a person in. Like alcohol, pot impacts each body differently and, until more research is done, Macdonald says we may be in the dark on a lot of answers.

“Hopefully, this will help to increase awareness,” he says. “Many people believe there is no risk, or that they can compensate by driving slower, but people used to say that about alcohol, too.” M

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