Cannabis-impaired driving

Driving while impaired by cannabis is a major safety issue on our roads. That’s why CAA is launching an awareness campaign encouraging young drivers to plan a safe way home if they plan to consume cannabis edibles. The message is clear: when you’re not fully in control of your body, you shouldn’t be behind the wheel.

Do you know all there is to know about cannabis and THC?

“Driving after smoking or ingesting cannabis is a bit like driving without your reflexes, your judgment, your concentration and your ability to determine the distance of the car in front of you.”

Nicolas Tétreault, PhD, Clinical Biochemist and Member of the Ordre des chimistes du Québec – Partner of the Foundation. 

Is the high from edibles really that hard to gauge?

To find out, CAA-Quebec talked to Dr. Nicolas Tétreault, a clinical biochemist and member of Quebec’s order of chemists—a CAA-Quebec Foundation partner.

The following summarizes his answers to our questions.

Edibles are probably the most unpredictable type of cannabis product. They take longer to kick in (up to 2 hours vs. just a few minutes when smoked), which means users are more likely to misjudge the effects. That can lead people to take more or worse, get behind the wheel, believing they’re still apt to drive.

That can obviously be dangerous if someone starts feeling the effects while driving. It can make them sleepy, confused, or anxious, and also reduce their reaction time, which is crucial when you’re behind the wheel.

The Highway Safety Code is very clear on that point. There is zero tolerance for driving while high, regardless of the driver’s level of experience. Those caught breaking the rules face an immediate 90-day suspension of their driver’s licence. If you’ve taken an edible, just don’t drive!

The delay before you feel any effects isn’t the only difference between smoking and eating cannabis, as this table shows.

How it's taken

Onset

Peak

Duration

Inhaled

A few seconds to a few minutes

30 minutes

2 to 4 hours, sometimes more

Eaten

30 minutes to 2 hours

2 to 4 hours

Up to 12 hours

Obviously, it all depends on the quantity taken, the concentration, the person’s metabolism, and their general state.

Is there any way to get it out of your system faster?

No. Only your body’s metabolism can do that. You’ll need to be patient. If you smoke weed or take an edible, stay put or have a designated driver take you where you need to go.

Find out more about edibles

A quick overview of edibles

Edibles come in different forms, such as cakes, cookies, candies, capsules, and drinks. While popular, they come with their share of risks. But although the production and sale of edibles has been legal in Canada since December 2019, only a few have been greenlighted for sale in SQDC stores. 

What are they made of, exactly?

There are a number of ways to make edibles. The THC concentration depends on the part of the plant used to make the edible (leaf, stem, flower, etc.)  and how much is used. Knowing an edible’s THC concentration is essential. Taking too many edibles is a recipe for disaster, particularly for someone who isn’t used to the effects.

What happens, physically, when you smoke or eat cannabis? 

Dr. Nicolas Tétreault sums it up well: “When you smoke cannabis, the THC gets into your bloodstream quickly, via your lungs, which can make people feel a variety of things: euphoria, relaxation, but also confusion, drowsiness, a loss of certain abilities (concentration, reactivity), and even anxiety.”

He explains that the effects are potentially the same with edibles, but they take longer to kick in, since the THC has to travel through the digestive system, including the liver (which metabolizes the THC), before it gets into the bloodstream.

If a product’s THC concentration isn’t properly indicated or controlled using a rigorous process, that edible could contain a lot more THC than the user may think, and the effects may be much stronger than anticipated.

The duration of the effects of cannabis on drivers

There are several factors to consider in assessing the duration of the effects of cannabis, especially those that affect driving. These include:

  • Metabolic variance from one individual to another

  • The concentration of THC in the cannabis

  • The consumption method

  • The type of user (occasional or frequent)

  • Substances combined with cannabis (alcohol, for example)

That said, in general, when smoked, the psychoactive effects of cannabis can last from four to six hours. It’s important to understand, however, that faculties can be impaired for 24 hours or more. In addition, the intensity of these effects may vary from one dose to another and from one person to another.

What is THC?

THC, or Delta-9-Tetrahydrocannabinol, is the main psychoactive component of cannabis and is responsible for the effects felt by the brain during consumption. It is also through this component that the potency of cannabis is determined, expressed as a percentage of THC.

THC affects driver reflexes

The effects of THC (the main psychoactive component of cannabis) are manifold. They have effects on cognitive abilities that can impair driving: 

  • Increased reaction time (slowed visual perception)

  • Decreased ability to focus on an action

  • Decreased ability to make quick decisions

  • Disturbance of distance evaluation

Thus, if something unexpected occurs, such as a child running into the street after a ball, a driver may not react appropriately. 

Different ways to take cannabis

The most common way to consume cannabis is to smoke it. This method causes a significant loss of THC—up to 50%—because it’s destroyed by the intense heat.

Cannabis can also be vaporized. When heated in this way, several substances, including THC, get evaporated. This method of consumption is recommended in particular for therapeutic uses of cannabis.

Food and drinks can also be made using cannabis. The THC in these types of products is released slowly into the body. The effects can take longer than expected to kick in and can last longer, which can catch unsuspecting users off guard.

Note that no matter how cannabis is consumed, it must be metabolized and eventually eliminated by the body in order for the effects of THC to no longer be felt.

THC detection in motorists

The only roadside screening test approved by the Department of Justice Canada is a saliva test. And if it’s positive, it can be followed by a blood test and an assessment by a drug recognition expert (DRE).

The difficulty here is that the cannabis levels measured (in saliva or in the blood) don’t correspond to the effects felt by the brain. THC can also remain in the body for a long time after consumption without having any psychotropic effects on the brain. The work of DREs is therefore an essential part of the overall assessment of the situation.

Why has no limit been established, such as the “.08” level for alcohol?

A driver’s intoxication level depends on the amount of drugs or alcohol in his or her brain. For alcohol, the detection is simple. The amount of ethanol in the breath is measured, which is equivalent to the concentration of ethanol in the blood throughout the body, including in the brain, since alcohol dissolves in water and spreads evenly throughout the body.

The situation is much different for THC, which dissolves in fat rather than water. The amount of THC in saliva can be measured if it was consumed recently, but this amount doesn’t equate to the amount in the blood or brain, hence the importance of assessment by DREs.

Cannabis detection following consumption depends on the dose, the way it’s administered, the frequency of use and the individual’s metabolism. Of course, the test used and the matrix chosen will influence detection times.

Urine is used to measure abstinence and is not useful in estimating the degree of impairment. An average detection time of five to seven days is involved, and even more for chronic users.

Saliva is an attractive matrix for determining recent consumption. A very high concentration can be detected in the minutes following consumption and up to five hours after—even up to 48 hours after in chronic users.

Blood, like other matrices, cannot be used to measure the psychotropic effects felt in the brain. Blood THC can be detected up to 12 hours after a low dose and up to 30 hours following high doses.

Yes. Several methods of consumption are possible for cannabis, and the THC concentration is directly related to them. Since the effects felt vary according to the level of THC in the blood, there will be significant differences in the “experience” felt by the user.


Absolutely not. Studies have shown that cannabis use among young people under the age of 25 can have a very harmful effect on the brain because it’s still developing. In particular, THC can influence the establishment of neural connections. Frequent and long-term cannabis use starting in adolescence can even cause a decrease in IQ.

Cannabis products today are 5 to 10 times stronger than those of the 1960s and later!

More sophisticated growing methods and crossbreeding have greatly modified the average concentration of THC, including that in hashish.

Driving high is driving impaired

25% of drivers who took drugs in the past year claimed to have driven a vehicle while under the influence.

Source: SAAQ

TRUE OR FALSE? Police can tell if a driver has consumed cannabis.

True. In Canada, police officers can stop vehicles and administer roadside tests. Their methods for detecting impairment include testing devices and calling in specially trained drug recognition officers.

Combining cannabis and alcohol multiplies the risk factor for driving more than either substance taken separately.

TRUE OR FALSE? Cannabis doesn’t affect your ability to drive.

False. Driving under the influence of marijuana affects your ability to drive safely and increases the risk of getting into an accident.

Be cautious and take small amounts, especially if it’s something new for you.

Not as bad as alcohol? It’s not a contest. Cannabis reduces your ability to drive and increases the risk of being involved in an accident. That’s a scientific fact.

Cannabis and driving: everything is more dangerous!

  • Coordination is reduced.
  • Reaction times are longer.
  • Concentration is more difficult.
  • Decision-making abilities are affected.
  • Ability to judge distances worsens.

Source: Government of Canada

Cannabis and travel: What you need to know

  • Canadian law is clear: it is illegal to get out of the country with cannabis, in any shape or form, regardless of the amount. It applies also to medical marijuana.
  • Pot is illegal in many countries. Travellers may be deemed inadmissible and subject to serious criminal penalties if caught with cannabis at the border.
  • Cannabis is legal in 10 US States, but remains illegal according to federal law. Consequently, it is forbidden to enter the country with the substance.
  • Canadian travellers who do not carry cannabis and have never committed any criminal offence related to drugs should not be worried, even if they used their credit card at the Société québécoise du cannabis (SQDC).
  • It is allowed to travel with cannabis inside Canada by either car, boat, train or airplane, but it is important to know the laws and rules in place in the visited province.
  • Travel insurance: The rules did not change. Insurers will refuse to cover a condition or an injury that occurs as a result of drug or alcohol use. And an insurer may refuse to compensate a traveller who runs into trouble owing to use or possession of cannabis.

What has been said about cannabis

Between 2011 and 2015, 30% of drivers aged 16 to 24 killed in road accidents in Quebec had marijuana in their system.