The skinny on cannabis and impairment

In the last three decades, Canada and the U.S. have seen a pronounced drop in alcohol impaired driving. The social acceptability of driving drunk, or allowing others to drive drunk, has changed dramatically. Alcohol’s effects on the ability to operate a vehicle are no longer up for debate; alcohol impairs driving skills and drunk driving kills. Alcohol has gone from a prohibited substance to being normalized within a generation. Those years allowed for things like legal blood-alcohol limits, reliable testing, public programs discouraging risky behaviours to be developed, and in the process a new cohort of adults to grow up understanding the risks of getting behind the wheel drunk.  

But cannabis hasn’t been granted the same time nor the consideration for normalization. The acceptance and regulation of marijuana has been tumultuous. However, public perception takes time to adjust, and some behaviours will need to change to ensure that public safety is of top concern.  

IRTAD Road Safety Annual Report (2015) showed that of the developed nations, Canada ranks number one in impaired driving deaths due to alcohol. In 2015 there were over 72,000 incidents of impaired driving reported by law enforcement. Alcohol aside, cannabis is the most frequently occurring drug in the systems of these drivers in crashes where intoxicants are involved. While the decrease in drunk driving is a significant achievement, driving under the influence of cannabis has not slowed down (Allen, M. 2016). If the impacts of legalization on impaired driving are to be reduced similar to how alcohol was, we must first understand the effects of driving high. 

Marijuana use has increased in certain demographics since legalization. And the rate of use may have lead to the normalization of driving under the influence of cannabis. Looking back in time, 8.6 per cent of nighttime drivers had the presence of THC in their system according to a 2007 National Roadside Survey of the National Highway Traffic Safety Administration (Compton R, Berning A, 2007). As of a 2014 study, this figure has increased to approximately 13 per cent in the United States, where marijuana use is federally restricted. 

THC and driving 

While marijuana will intoxicate the user, equating the effects to alcohol is an erroneous leap. Ethanol and THC are different molecules, have different effects on the body and different effects on driving. Driving simulators can shed light on the risk of cannabis use while driving, while demonstrating how driving quality changes and to what degree. The simulators corroborate much of what has been said about driving high: cannabis impairment tends to cause reduced travel speed in comparison to alcohol and cannabis impaired drivers tend to be less aggressive in their driving behavior (Grotenhermen, Leson, Berghaus, et al., 2005). Those rejoicing in the data should be aware that despite cannabis users attempt to drive safely, they are still at a significantly higher risk of motor-vehicle accident than a sober driver. THC will increase reaction time and can cause spatial-temporal changes, which has an effect on time and space perception.  

First-hand reports from cannabis users who choose to drive impaired tend to state that they drive slower than they would under the influence of alcohol and with more care. However, this isn’t something that can be safely and ethically verified without the use of driving simulators.  

Why 5ng/mL? 

Many jurisdictions have strongly endorsed a 5ng/mL blood THC limit. This decision has both critics and supporters in their respective cannabis camps. But, like everything cannabis related, the science should be looked at before an opinion is made. Dr. Olaf Drummer has done extensive work on the factors that cause car-crashes for over 20 years. Drummer looked at the odds ratios of accidents under certain conditions. An odds ratio will demonstrate how many times more likely an incident is to happen with drugs or alcohol present. The odds ratio of a crash with a blood-alcohol content of 0.15 per cent is 6.6. That means you are 6.6 times more likely to have a fatal car accident with that blood alcohol content. With a delta-9 THC concentration of 5ng/L, the odds ratio is similar. 0.15 per cent blood-alcohol is double the legal limit in most jurisdictions. Taking this into account, many policy makers have made their legal limit half of that concentration — 2 ng/mL. The reasoning comes from assuming THC is like alcohol: half the substance, half the effect, and half the impairment. Instead, halving the substance would not halve the impairment but would eliminate the impairment altogether. Alcohol acts very predictably. It will disperse itself in body fluids evenly regardless of whether the fluid is blood, saliva or sweat. Alcohol then is removed from the body in a linear and expectable fashion. On the contrary, THC and its metabolites are highly lipophilic, or “fat-loving”. Thus, the substance will favor certain fluids (and tissues) over others. THC and its metabolites are stored in our fat cells and eliminated very slowly over time. 3-hours after consumption, the odds of a vehicular accident decrease to statistical insignificance (Blow, et. al, 2005). The serum THC level peaks and then is quickly eliminated after a few hours.  

The carboxy-THC (the by-product of THC in the body) metabolite can be detected approximately 1-week after an isolated inhalation of marijuana, but for heavy and everyday users this may take several weeks, if not months. Your occasional recreational cannabis user could use marijuana on a Friday night, abstain over the weekend, be completely sober on Monday morning and still test positive for cannabinoid metabolites despite no impairment or loss of function whatsoever. 

Law enforcement has daunting task with identifying those under the influence of cannabis. The lagging technology may not have a standard cannabis breathalyzer for many years or ever. Training has begun for roadside testing of impairment involving tasks and physical signs to detect impairment including: resting muscle tone, pupil dilation, balance, reaction time and other metrics. The police have gone back to observational criteria to ensure the sobriety of a driver.

The problem with mixing substances. 

The use of cannabis for recreational purposes can often go hand in hand with other intoxicants.  The more marijuana becomes legally permitted and normalized in everyday use, the more we will see effects of combining alcohol, prescription drugs, illicit drugs and others. The notion that cannabis is natural and therefore the dangers of intoxication (and severity of outcomes) are minimal is simply not the case. To reduce the risks, some users will simply stick to lesser amounts of alcohol and lesser amounts of cannabis. The user believes that they have not compromised their sobriety because they’ve used less of both. However, combining substances has an additive effect. Lesser amounts of THC in a system where alcohol is present may feel like a greater amount to the user and will impair more than the presence of just one intoxicant. Simply put, our livers make a point of selectively filtering out certain substances over others. As one is metabolized preferably we will see the metabolism of others slow down leading to accumulation in the system and prolonged impairment. If you combine cannabis and alcohol you will be higher for longer and the side effects of each will be amplified.  With edible products, the strain on the liver is greater than with smoking due to oral consumption undergoing first-pass metabolism. Here the liver will transform the active ingredient of THC to a more potent molecule that will increase the risk of feeling sick, paranoid or uncomfortable (dysphoria). Adding alcohol to the mix only exacerbates this phenomenon. 

Education was the catalyst that allowed for Canadians to realize the harmful impacts of impaired driving. Organizations like MADD and incorporating education into secondary school curriculum lead to a societal shift in perception. The change in attitude leads to a change in behaviour. A little bit of knowledge goes a long way when the learning curve is so steep. There are still legal and cultural hurdles ahead. Public safety must be paramount in the minds of administrators, retailers and regulators moving forward.

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If you have questions about harm reduction, safe usage or anything else under the banner of cannabis, book a virtual appointment with Dr. Ife Abiola.