Legally determining impairment from pot not as clear as we thought

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We have decades of studies about the impact of alcohol on our brains. We have decades of research about the impact of cannabis on our brains. What we don’t have is knowledge about the combination of both substances on a driver’s brain — and yet that is precisely the area where incidents are increasing. 

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The Traffic Injury Research Foundation (TIRF) recently released a study  exploring the increasing risk of this cross-pollination. There’s a move in recent years from calling it “drunk driving” to labeling it what it is: impaired driving. While impairment can be caused by fatigue, distraction, drugs or alcohol, police and crash data is increasingly showing impaired drivers test positive for more than one substance. 

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The study reveals the knot of combining drugs — specifically marijuana — and alcohol: “One reason the combined use of alcohol and marijuana has more significant impairing effects on driving skills is the interaction between the drugs can increase risk-taking and users are less likely to recognize the potential negative consequences.” Alcohol makes you do risky things; pot makes you less likely to interpret the danger. 

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“Canadians were asked how many times they had driven a motor vehicle within two hours of using marijuana in the past 12 months. In 2020, results showed 4.5 per cent of drivers reported this behaviour,” reports a TIRF study . Numbers went up after legalization in 2018 (3.3 per cent), and went up more in 2019 to 7 per cent. One thing not factored into these numbers is a global pandemic that saw our road traffic drop off a precipice; I’d guess 2021 numbers will climb again. 

As the legalization of cannabis grows, you’d think governments would be eager to define impairment. You’d be wrong. According to Bruce Haycock, a scientist at the Toronto Rehabilitation Institute needed research simply isn’t happening. “The whole University Health Network (UHN) has been unable to secure licencing to do research with cannabis. The research is basically where it was in 2018.” I asked how you design legislation, create laws, and determine punishments with no research to base all these things on. “You don’t. It’s a total crapshoot,” admits Haycock.

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The Institute has one of the best driving simulators in the world. They’ve been doing research on the impact of medical marijuana for years, yet can’t conduct studies on the impact of something the general public is now legally allowed to use? Haycock points out that any studies that have been done, as one in Israel , predominantly use participants they have at hand: university students. We need more relevant testing to extrapolate better results. He further points out that the results of every study on marijuana usage and driving show people drive slower and leave more space. “Isn’t that what we keep wanting?” he laughs. All kidding aside, if reasonable cannabis consumption and a sufficient delay after that consumption has no detrimental effect on driving, why are we leaving our courts open to so many charges that will inevitably be thrown out? Do the research; make good laws.

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As my colleague David Booth reported way back in 2016, nobody can really find that being under the influence of a little weed is much of a problem in most cases. We’ve spent so much time and energy defining how alcohol is a scourge on our roadways that we’re looking for an equivalent demon in the cannabis ranks, and it’s not showing up. The fact that THC can remain — measurably — in your body for weeks after consumption also muddies the waters. Are you high, or were you high? The entire rat’s nest surrounding edibles is more reason to get definitive studies going. If we’re selling it, we need to know the impact.

The National Institute of Justice (U.S.) in April released a report stating, “ although THC has been proven to affect areas of the brain that control movement, balance, coordination, memory and judgment — skills required for safe driving — THC levels in biofluids were not reliable indicators of marijuana intoxication for their study participants.” We’re not effectively testing the right thing.

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What is a problem is combining alcohol and weed, which is occurring more frequently. According to TIRF, “[s]ince 2015, Canadians were also asked how many times they had driven a motor vehicle within two hours of using marijuana and alcohol within the past 12 months. In 2020, 2.1% of Canadians reported this behaviour,” an increase of 24 per cent over 2018. 

Robyn Robertson at TIRF agrees that typically, medical marijuana users have a higher tolerance due to more frequent use, and are less likely to be impaired than occasional users. It’s why speaking of impairment is more important than seeking specific numbers. “Alcohol is water-soluble and is distributed throughout the body. We can say .08 (or .05 in many places) is a measurable level of impairment. Drugs are soluble in fat, and we just don’t have a standard dose-response concentration number.”

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Saliva testing devices debuted to much fanfare around the world, including in Canada when legalization descended. Some police are also specially trained Drug Recognition Experts using 12-step sobriety tests. The NIJ report states, “ the results of the study seem to indicate that both tests could be completely unreliable factors in determining whether someone is capable of driving,” when it comes to cannabis.

In 2019, a Nova Scotia woman, Michelle Gray , had her licence suspended for 7 days, her vehicle was impounded and she was arrested after testing positive for cannabis at a police checkpoint. At the station, she was administered a further sobriety test which she passed. Gray has MS, and uses medical marijuana. The RCMP apologized two weeks later. 

We need impaired drivers off our roads. We also need current research to know what they’re being charged with to target the right ones, and a clear, fair way of determining that. Alcohol and cannabis are two different beasts, but are both legal substances. Let the scientists do the work so we make legislation that protects road users — and holds up in court.