Study Shows Cannabis Use Does Not Affect Next-Day Driving

A recent study from the Centre for Addiction and Mental Health in Toronto has debunked a myth that cannabis can influence drivers up to 24 and even 48 hours after consumption.

Full story after the jump.

A study by the Toronto, Canada-based Centre for Addiction and Mental Health found that while drivers under the influence of cannabis shows signs of driving impairment immediately after consumption, they performed normally in driving tests 24 and 48 hours later, according to a Global News report outlining the study.

The study, using a driving simulator, allowed participants to control their own cannabis consumption, which varied the THC in the blood of the subjects and ranged from zero to 42 nanograms per milliliter – which is about 10 times more than the legal limit in Canada.

Immediately after smoking, the group that consumed THC drove inappropriately slowly and centered the simulated car in the lane poorly.

“We found significant evidence of difference in driver behavior, heart rate and self-reported drug effects 30 minutes after smoking cannabis, but … we found little evidence to support residual effects,” the researchers said.

Scott Macdonald, a retired professor at the University of Victoria, said the nation’s drugged driving laws – which require no trace of THC when operating a vehicle – are “not scientific” and argued that the 24-hour after-effects of cannabis are a myth.

“When people smoke cannabis, they’re only impaired for a short, short period of time. You could have THC in your bloodstream, but you’re not a danger,” he told Global News.

“The biological tests are not useful for identifying people that represent a safety risk. What we’re left with is behavioral symptoms. We’re still working on developing tests to assess whether an individual who consumes cannabis is a safety risk. It’s hard to do. Cannabis is not in the same class as alcohol, in terms of safety risk. Alcohol is much, much worse.” – Macdonald, to Global News

Drugged driving laws throughout Canada vary – in Ontario, drivers found with any THC in their system face a three-day license suspension, $250 fine, and $281 reinstatement fee for their first offense. In Saskatchewan, new drivers face a 60-day license suspension, three-day vehicle seizure, and four points.

In Saskatoon, Saskatchewan’s largest city, police reported that just eight of 292 driving while impaired violations from Oct. 17, 2018 to Oct. 17, 2019 were directly related to cannabis intoxication. Since July 2019, the agency has employed a Draeger 5000 Roadside Screening Device “at every sobriety checkpoint” to test for both cannabis and cocaine and have used it 12 times; nine drivers tested positive for THC, while two drivers were cleared of driving under the influence due to the device’s results.

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