Driving & Cannabis

Driving under the influence of Cannabis


Studies have indicated that the use of THC cannabis while driving impacts your:

  • Reaction time
  • Visual function
  • Concentration
  • Divided attention
  • Following distance
  • Speed 


THC cannabis can impair judgment and performance in a naïve patient. It also compromises your ability to handle unexpected events, such as a pedestrian darting out on the roadway and doubles your risk of a collision.

Therefore, driving, operating heavy machinery or safety sensitive activity should be avoided if possible. If using cannabis daily, THC tolerance may develop and there may be minimal impairment (similar to tolerance to opioids). However, this does not mean it is safe to drive. You should not drive until you become accustomed to the effect of the cannabis. The acute effects of inhaled cannabis subside generally after about 3 hours.

Many argue that if the CBD content and the THC content are equal, they cancel out and you won’t have any side effects. However, there are no studies to suggest this is true when it comes to driving. However, taking only CBD cannabis, will give you no psychoactive effects and may be an option for circumstances requiring high cognitive function.

Although the weight of evidence clearly reveals significant psychomotor impairment as a result of THC cannabis use, it is difficult to predict the extent to which a given amount of cannabis will have on a particular individual.

Patients must use their own judgment when using cannabis, narcotics, muscle relaxants, alcohol or any other substance which can reduce cognitive abilities.


There are no specific laws or roadside testing procedure for cannabis. However, if you are pulled over, a police officer may make a demand for you to do a Standard Field Sobriety Test (SFST). A SFST test is typically administered roadside and consists of a police officer putting a suspected impaired driver through a series of standardized sobriety tests.

Drivers who are impaired by drugs are subject to the same penalties as those impaired by alcohol.

Do not drive if you feel impaired or intoxicated. By using cannabis in a safe and conscious way, you are protecting your life as well as the lives of those around you!

Check your Provincial/Territorial laws to determine what administrative penalties may be imposed upon you, in addition to any criminal penalties, for impaired driving where you live.

For more information, go to http://www.rcmp-grc.gc.ca/ts-sr/aldr-id-cfa-aldr-eng.htm.

As well as the articles:

  1. “How high is too high to drive?” http://www.cbc.ca/news/canada/british-columbia/how-high-is-too-high-to-drive-1.3415951
  1. “When is stoned too stoned?” http://news.nationalpost.com/news/canada/0518-na-stoned



Asbridge, Hayden, & Cartwright 2012.

Canadian Centre on Substance Abuse, 2014.

Ashton, 2001; Berghaus & Guo, 1995; Hartman & Huestis, 2013; Ramaekers, Robbe, & O’Hanlon, 2000

Downey, et al., 2013; Ramaekers, et al., 2000

Hartman & Huestis, 2013

Drummer et al., 2004; Laumon, Gadegbeku, Martin, Biecheler, & the SAM Group, 2005; Mura, et al. 2003

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