Does Marijuana Use really affect your Driving Ability?

Posted by Stevenson Whelton MacDonald & Swan
October 21, 2018

A recent Health Canada survey found that 39 per cent of persons who admitted to smoking pot drove within 2 hours of doing so.  Much higher is the number of pot users who said they were passengers in a vehicle driven by someone who smoked pot.  Almost 80 per cent admitted they got into a vehicle with someone who used marijuana within 2 hours of driving.

What’s particularly disturbing for many Canadians is that half of pot users have stated that they don’t believe consuming marijuana interferes with their ability to drive.  This rate is much lower than the percentage of all respondents, 75 per cent, who said they think marijuana affects their driving ability.

What does research tell us on this subject?

Early research on the impact of cannabis on driving performance was conducted in laboratories and through driving simulation studies.  These studies consistently found that increased doses of cannabis impair a person’s psychomotor skills, which are fundamental skills for safe driving.  However, these studies did not always translate directly to real world driving scenarios, including complex driving situations in natural settings.   

Observational studies of marijuana use and motor vehicle accidents addressed many of the shortcomings of laboratory studies.  These studies examined the incidence of cannabis consumption for injured or fatally-injured drivers and the general public, and found that, after alcohol, marijuana is consistently the most frequently detected psychoactive substance.  It was concluded that drivers who used marijuana within two hours of driving had higher rates of being involved in an accident.  

Controlled research studies that investigated how cannabis consumption correlates with the risk of collision have had more inconsistent results.  More than half suggest that cannabis consumption increases the risk of a motor vehicle accident, but the remaining studies found no relationship between cannabis use and collision risk.  And, culpability studies or case-controlled studies that looked at drivers who were involved in collisions and compared cannabis use among drivers who caused the collision with the drivers who did not, also had inconsistent results.

A comprehensive and systematic review was recently carried out, and analyzed many observational and case-controlled studies that investigated the impact of cannabis use on driving, and include a control group.  The review included studies from different countries and it excluded low-quality studies which were lacking in objectivity in their methodology and analysis. Collisions involving all types of motor vehicles had been studied, including cars, light and heavy trucks, SUV’s, vans, motorcycles, buses, ATV’s and snowmobiles.  The review attempted to separate out the impact of other psychoactive substances including alcohol, which has often confounded other study outcomes.

This systematic review and analysis of research results concluded that acute cannabis consumption almost doubled the risk of a driver being involved in a motor vehicle accident resulting in death or serious injury.  The high quality and case-controlled studies, and the studies of fatal crashes, had the strongest results indicating increased risk.  However, the connection between acute marijuana use and minor collisions was not clearly determined in the studies.  

The finding that cannabis consumption impacts collision risk should be a wake-up call for any marijuana users who remain sceptical that driving under the influence of pot doesn’t undermine their ability to drive.  The Government of Canada has stated that accident statistics show that driving under the influence of drugs is a major factor in fatal motor vehicle accidents.  And when such accidents occur, the drug-impaired drivers are often not the only victims - passengers and other road users are just as vulnerable to injury or death resulting from DUI collisions.

If you or a loved one were injured in a motor vehicle accident caused by a negligent driving action, call an experienced car accident lawyer at Stevenson Whelton MacDonald & Swan.  We welcome your questions and can provide an honest assessment of your case, so that you can make an informed decision on whether to proceed with a personal injury claim.

Disclaimer: Our blog is intended to inform our existing and prospective clients about topics pertinent to their lives. While our goal is to provide accurate and factual information, this in no way should be taken as legal advice or applied to specific cases. It is in your best interest to contact a licenced and practising lawyer for legal representation, as matters of the law are often complicated and cannot be fully assessed without knowing all of the details of a case.