Newfoundland research team spoke to 91 youth and young adults over the summer of 2021 to get their perspective.

Cannabis is the  second-most widely used substance  in Canada, after alcohol. While there is an in-depth understanding of the  impact of alcohol on driving , cannabis is a much more complex substance and can affect consumers differently depending on the product type, amount used and a person’s potential tolerance.

Driving under the influence of cannabis

A recent study has shown that  the legalization of cannabis has not increased the rate of traffic accidents or injuries resulting from driving under the influence of cannabis . Care must be taken to not misinterpret this as cannabis being safe.

A 2012 analysis summarizing nine earlier studies on cannabis and driving showed that  cannabis doubled the risk of a fatal or serious injury crash . Cannabis-impaired driving was associated with  four to 12 per cent of all injuries and mortalities from motor vehicle accidents in Canada in 2012 . The reality is that Canadians have been engaging in risky driving behaviours even before cannabis was legal.

Another study, conducted by Public Safety Canada in 2017, reported  even higher rates of cannabis-impaired driving, with 28 per cent of those who consumed cannabis indicating that they had operated a vehicle impaired .

Cannabis impairs driving differently than alcohol

Driving needs full concentration , and making the right decisions at the right time can save lives. Cannabis containing  tetrahydrocannabinol (THC)  affects motor co-ordination and reaction time, can cause hallucination and increases the risk of getting into a collision. Many studies show strong evidence that  cannabis use negatively affects performance on driving-related cognitive tests on a variety of driving tasks .

Alcohol consists of a single chemical that has been well studied for decades. It has a reliable test that measures blood alcohol levels and those blood alcohol levels match to  levels of impairment . Cannabis on the other hand consists of several chemicals that lead to varying levels of impairment.

THC is the chemical we know the most about and the one that leads to the  greatest impairment  from cannabis. However, other less studied chemicals may also impair driving, and we are only at the beginning stages of learning about these effects. There are  roadside tests  to detect levels of THC in the blood, but the relationship between those levels and impairment is not as clear as those with alcohol.

Factors that affect impairment

It is difficult to predict the exact effect cannabis will have on a particular individual. Impairment can be based on many factors, including the dose of THC, personal experience with cannabis, individual biology and the route of consumption (for example, inhaling versus edibles).

There are several types of cannabis products on the Canadian market, and each product has a different amount of THC and takes a  varying amount of time  to reach its full effects. The following outlines typical time to effect and duration of impairment.

Safety considerations when driving

Cannabis-impaired driving is very risky. It is difficult to advise exactly how long someone should wait after consuming cannabis before driving. The safest choice is to separate cannabis consumption from driving entirely.

However, there are  several strategies  to avoid this risky situation, including:

Many young people believe that it is difficult for police to detect and charge drivers who consume cannabis. However, signs of intoxication  (bloodshot eyes, smell of cannabis, shallow breathing or rapid heart rate) can form a reasonable suspicion for police. In addition, there are three tests of the Standardized Field Sobriety Tests (SFST)  (horizontal gaze nystagmus (involuntary eye movements), one-leg stand and walk and turn) that are performed to evaluate impairment.

In Canada, the Criminal Code prohibits driving while impaired. Penalties range from a minimum fine to imprisonment, depending on the severity of the offence. Impaired drivers who cause injury or death can face longer periods of incarceration, including imprisonment for life.

A Health Canada survey showed that  very few parents (11 per cent) said they had discussed the risks of driving under the influence with their teenagers . However, only four per cent of teens indicated they had discussed impaired driving with their parents.

It is essential to start a conversation with children and teens about the risks of driving under the influence of cannabis. Our CHERP research team’s  public engagement events  and social media ( Twitter and Facebook ) can provide information and resources. Young people need to be prepared to make  informed decisions  long before they are ready to get behind the wheel.