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September 18, 2018  •   6 minute read

Marijuana and Driving - What You Need to Know

With marijuana legalization going into effect, Canadians need to talk about safe use.

The vast majority of Canadians understand that driving under the influence of alcohol poses a serious threat to safety, but there’s less consensus about marijuana. While 75 per cent of Canadians believe using marijuana affects driving, only half of marijuana users agree.

With the legalization of marijuana across the country, there will soon be a lot more users, and some of them will be on the road. It’s time to have a national conversation about safe use, and make sure consumers — along with their friends and families — understand the risks.

Marijuana isn’t the scourge we once treated it as, but it is a mind-altering chemical that can impair your coordination and focus. Make sure to learn how your body and mind react to it, and take the time to sober up before getting back on the road.

Marijuana and Driving: Challenges of Legalization

When the Cannabis Act goes into effect on October 17th, Canada will become the second nation in the world to legalize marijuana on a national level. This law reflects public opinion.

Canadians have a relaxed attitude towards marijuana use, with a majority of Canadians (68 per cent) support legalization, and nearly half (45.8 per cent) expressed a desire to buy “marijuana-infused food products” if and when they become available commercially.

While this law may be the right policy overall, it poses certain challenges from a vehicle safety and law enforcement perspective that’s different from those posed by alcohol. The dose-dependent effects of drinking are well studied. We have a good understanding of how much alcohol you will have in your body after a certain number of drinks, how long it will take to metabolize, when it is safe to drive and when it isn’t.

We can enforce those rules with breathalyzer tests that measure how much alcohol is in the bloodstream and spot signs of intoxication, which are pretty consistent between people.

Marijuana is different. It’s very difficult to measure dose when it is inhaled, and the onset of effects can vary depending on how it is consumed. The effects and degree of impairment can also vary a lot between people. And unlike alcohol, THC (the chief psychoactive component of marijuana) can stay in the bloodstream for a month, making it very difficult to link dosing to degree of impairment.

Breathalyzers now exist, but they aren’t a good proxy for degree of impairment in the same way alcohol breathalyzers are. That leaves officers to depend on less scientific standards for determining whether a driver is stoned.

All these factors make it difficult to set and enforce standards of what constitutes impairment even from a legal perspective, to say nothing of a cultural standard. Defining what constitutes a safe interval between consuming pot and driving is tricky. Here’s what we do know:

  1. Fact 1 Cannabis Use Affects Driving in Different Ways Than Alcohol

    The stereotype of the overly cautious stoned driver, going way under the speed limit has a basis in fact. According to a review of studies on the effects of marijuana and alcohol on driving published in the American Journal of Addictions, stoned drivers tend to be aware of their intoxication, and compensate. Commenting on the fact that some studies do not show impairment in driving simulations, the authors noted:

    “Many investigators have suggested that the reason why marijuana does not result in an increased crash rate in laboratory tests despite demonstrable neurophysiologic impairments is that, unlike drivers under the influence of alcohol, who tend to underestimate their degree of impairment, marijuana users tend to overestimate their impairment, and consequently employ compensatory strategies. Cannabis users perceive their driving under the influence as impaired and more cautious — and given a dose of 7 mg THC (about a third of a joint), drivers rated themselves as impaired even though their driving performance was not; in contrast, at a BAC 0.04%... driving performance was impaired even though drivers rated themselves as unimpaired.”

    In other words, stoned drivers don’t suffer from the recklessness and poor decision-making often associated with drunk drivers. On the contrary, there’s evidence that drivers who have consumed cannabis tend to think they’re more impaired than they really are, and they drive cautiously to compensate — even when they’ve only consumed a small amount of marijuana. They typically drive slowly and are less likely to overtake and pass other drivers. On the other hand, drivers tend to underestimate the effect of alcohol. Even small amounts of alcohol can cause them to take more risks and impair driving performance.

    However, that doesn’t mean marijuana and driving are a safe mix.

  2. Fact 2 Marijuana Does Impair Driving

    Stoned drivers may be able to compensate for some aspects of their intoxication, but there are some effects of driving stoned you can’t compensate for. Particularly in high doses, marijuana can negatively impact a broad range of cognitive abilities, such as:

    • Attentivenes
    • Motor coordination
    • Object trackin
    • Time and speed perceptio
    • Ability to divide attention to perform complex tasks

    Driving slowly and conservatively may lessen the risks of driving impaired, but it doesn’t eliminate them. Driving is filled with unexpected events that require quick reactions.

    At any point, you may have to react to a quick light, a nearby car swerving, traffic stopping or a pedestrian suddenly dashing out into the street. Marijuana can slow your reactions, making it harder to stop or maneuver out of the way in time. It can also make it harder to stay in your lane.

  3. Fact 3 Cannabis Can Have Idiosyncratic Effects

    All drugs affect different people differently, but with marijuana the differences can be dramatic. Some people become very outgoing and socially at ease when they smoke or otherwise ingest cannabis, while other may feel anxious or uncomfortable in large groups.

    Some users get intellectually stimulated and engaged when they consume, while others mentally turn off and zone out. The strain, mode of consumption, current mood of the smoker, fatigue and other factors help shape the way the user reacts as well, and results can vary significantly from one session to another.

    That has important implications for marijuana driving impairment. Some users may not be able to drive safely on even a small amount of marijuana, because of the way it affects them. Others will be less strongly affected by a small dose.

  4. Fact 4 Marijuana Impairment Increases With Alcohol Use

    Because alcohol and marijuana impair driving in different ways, consuming them together can exacerbate the effects of both. Drivers may lose the inhibition associated with driving after consuming marijuana, meaning they’re no longer compensating for its effects.

    On top of that, they’ll be affected by alcohol which, as we said, impairs driving skills even at low doses. Drivers should exercise extreme caution when combining both drugs, and make sure to leave enough time to sober up before they get on the road. Or better yet, bring a designated driver along.

  5. Fact 5 It Can Be Difficult to Gauge When You’re Sober

    There are good rules of thumb for alcohol consumption and sobriety. Alcohol metabolizes at a steady rate. It can vary between individuals and based on food intake, sex, age and other factors, but generally speaking, your body processes about one drink per hour. This makes it pretty easy to enjoy a night out, have a few drinks and leave time to drive home sober.

    With marijuana, even understanding your dose can be a challenge. A toke can be a radically different quantity depending on the strain, whether you consume it from a bowl, joint or vaporizer, and other factors. Throw in edibles, and things get even more complicated. Peak intoxication from smoking occurs quickly, and the strongest effects tend to fade within a couple of hours. But edibles can take an hour or more to peak, and the high can linger much longer.

    Additionally, marijuana can exhibit reverse tolerance. Many users experience little to no effect the first time they smoke, and much stronger effects on later occasions. For inexperienced users, this can make it hard to plan a safe margin of time for driving after partaking.

    There are studies underway to determine precisely how long the effects of cannabis last, but there really isn’t a solid scientific consensus, or even a “one drink per hour” style rule to follow. If you plan to partake (or you’ve consumed marijuana already) you should leave ample time before driving and err on the side of caution.

    Even if several hours have passed, it’s good to take a few moments to yourself and evaluate your own mental state before you drive. Are you alert, or do you feel hazy? Are you able to multi-task and react quickly to things going on around you, or are you having mental tunnel vision, where you become deeply engrossed in one thing at a time?

    Be honest with yourself, and don’t take unnecessary risks — even if you’re pretty sure you’re ready to drive.

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Have a Good Time, But Use Good Judgment

For the first time since 1923, Canadians are about to be able to consume marijuana legally.

For almost a hundred years, we’ve treated pot as a dangerous enough drug that it warrants prosecution and imprisonment. As Canada rolls out legalization, there’s a danger that new users will swing too far in the other direction and underestimate the risks of using marijuana and driving.

Marijuana isn’t the scourge we once treated it as, but it is a mind-altering chemical that can impair your coordination and focus. Make sure to learn how your body and mind react to it, and take the time to sober up before getting back on the road.

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