DISCOVER CANNABIS

The Science of Cannabis and Driving

How does cannabis impact driving? Learn what researchers have learned that can help you make good choices in your consumption routines.

No one gets up in the morning wanting to have a traffic accident. But if you drive under the influence of cannabis, studies show you’ll be at least twice as likely to get involved in a crash1. Read on to learn how cannabis affects your driving ability so you can plan for safe travels.

How Does Cannabis Affect Your Ability to Drive?

Cannabis is a beautiful and complicated plant. It contains over 400 active compounds that have a variety of effects in our body and behaviour2 3 4. One of the most notable effects is euphoria, or a “high,” which comes from delta-9-tetrahydrocannabinol (THC). The feeling of euphoria can help some people relax so they can sleep5 or cope with pain6, but it also interferes with a person’s ability to drive7.

Studies show that people who have recently consumed cannabis or who have THC levels of at least 2 ng/ml can experience substantial driving impairment8.

THC can affect your ability to drive by9 10:

- Making you slower to react, like hitting the brakes when a pedestrian steps off the curb
Making you bad at complex tasks, like reading road signs while you drive
Making you weave in and out of your lane
Making you forget what just happened, like whether the merge-lane you just checked was clear

 

Cannabis Driving Laws in Canada

What Happens During a Traffic Stop for Cannabis? 

For law enforcement, figuring out whether a person is driving under the influence of cannabis (DUIC) is more complicated than assessing them for alcohol. In an August 2019 interview to CBC News, Constable Andrew Fairman said the Calgary Police Service’s traffic section was still in the process of training officers to recognize the particular signs of cannabis impairment. Some visual symptoms include dilated pupils, lapses of attention and concentration, and reddened eyes11.

However, an officer does not need to be certain that cannabis is the cause in order to arrest an impaired driver. If a police officer suspects someone is driving while intoxicated, they can have the driver perform a Standardized Field Sobriety Test (SFST). This usually involves walking in a straight line, standing and turning, or standing on one leg12.The officer can also ask a driver to provide a saliva sample that will be tested for the presence of THC using an approved roadside testing device13.

What are the Laws on Cannabis and Driving in Canada?

In Canada, there are two levels of DUIC that are specified in the Criminal Code under Impaired Driving Laws14.

If your blood measures 2-5 nanograms of THC per millilitre within two hours of driving, it is considered a less serious offence with a maximum fine of $1000. However, if your concentration is higher than 5 ng/ml, it is considered a more serious offence with penalties that can include up to 10 years imprisonment15.

Cannabis and alcohol are a dangerous combination that increases driving impairment and the likelihood of a crash16. In Canada, the legal limit for THC and alcohol in the blood is only 2.5 ng of THC per ml and 50 mg of alcohol per 100 ml. If blood testing shows a prohibited mix of THC and alcohol, it is also considered a serious offence. There are additional penalties if you cause bodily harm or death while DUIC17.

Is There a Recommended Wait Time Before You’re Safe to Drive?

There are too many factors that influence your impairment level to recommend a specific wait time before you can safely drive after using cannabis.

How long a person feels “high” can depend on the amount of THC they consume, how they consume it, and the person’s individual tolerance level and metabolism. The results can vary widely from person-to-person. For example, one study showed that when a group of occasional users smoked a mid-level dose of THC (between 13-17.5 mg), it impaired their driving abilities for anywhere from 10 minutes to 7 hours18. That range can be even wider for edibles.

If I Don’t Feel High, Am I Ready to Drive? 

An important fact for cannabis consumers to know is that even after the sensation of being “high” has passed, you can still be functionally impaired. Judgement and coordination tasks have found that people can still be impaired as long as 24 hours after the feeling of being “high” has passed19.

How Do I Plan for Safe Driving if I Use Cannabis?

Because the results of THC can be so unpredictable, it is recommended that you never drive after taking it in any form.
If you consume occasionally, you can plan ahead to travel safe.
Enjoy your cannabis on a day when you have nowhere to go
Arrange for a sober friend to give you a ride or to be the designated driver
Bring your PJs and stay overnight after an infused meal or party
Carpool, take public transit or book a ride-share
Use Google Maps to plot a route by foot

 

References

[1] Hartman RL, Huestis MA. Cannabis effects on driving skills. Clinical Chemistry. 2013;59:478+.

[2] Aizpurua-Olaizola O, et al. Targeting the endocannabinoid system: future therapeutic strategies. Drug Discov Today. 2017;22(1):105-110.

[3] Morales P, Hurst DP, Reggio PH. Molecular Targets of the Phytocannabinoids: A Complex Picture. Prog Chem Org Nat Prod. 2017;103:103-131.

[4] Atakan, Zerrin. Cannabis, a complex plant: different compounds and different effects on individuals. Ther Adv Psychopharmacol. 2012;2(6):241-254.

[5] Babson KA, Sottile J, Morabito D. Cannabis, Cannabinoids, and Sleep: a Review of the Literature. Curr Psychiatry Rep. 2017;19(4):23.

[6] Li X, et al. The effectiveness of self-directed medical cannabis treatment for pain. Complement Ther Med. 2019;46:123-130.

[7] Hartman RL, Huestis MA. Cannabis Effects on Driving Skills. Clinical Chemistry. 2013;59:478-492.

[8] Hartman RL, Huestis MA. Cannabis Effects on Driving Skills. Clinical Chemistry. 2013;59:478-492.

[9] Hartman RL, Huestis MA. Cannabis Effects on Driving Skills. Clinical Chemistry. 2013;59:478-492.

[10] Beirness DJ, Porath AJ. Clearing the smoke on Cannabis: Cannabis Use and Driving – An Update. Canadian Centre on Substance Use and Addiction;2017.

[11] Beirness DJ, Porath AJ. Clearing the smoke on Cannabis: Cannabis Use and Driving – An Update. Canadian Centre on Substance Use and Addiction;2017.

[12] Legalline.ca. Roadside tests: Standardized Field Sobriety Test, Breathalyzer, and Oral Fluid Test. Legal Line. https://www.legalline.ca/legal-answers/breathalyzer-and-roadside-tests/. Published 2019. Accessed 13 Aug 2019.

[13] RCMP. Impaired driving investigations. Royal Canadian Mounted Police. http://www.rcmp-grc.gc.ca/ts-sr/aldr-id-cfa-aldr-eng.htm#sfst. Published 2018. Accessed 13 Aug 2019.

[14] Department of Justice. Impaired Driving Laws. Department of Justice. https://www.justice.gc.ca/eng/cj-jp/sidl-rlcfa/. Published 2019. Accessed 13 Aug 2019.

[15] Department of Justice. Impaired Driving Laws. Department of Justice. https://www.justice.gc.ca/eng/cj-jp/sidl-rlcfa/. Published 2019. Accessed 13 Aug 2019.

[16] Hartman RL, Huestis MA. Cannabis Effects on Driving Skills. Clinical Chemistry. 2013;59:478-492.

[17] Department of Justice. Impaired Driving Laws. Department of Justice. https://www.justice.gc.ca/eng/cj-jp/sidl-rlcfa/. Published 2019. Accessed 13 Aug 2019.

[18] Hartman RL, Huestis MA. Cannabis Effects on Driving Skills. Clinical Chemistry. 2013;59:478-492.

[19] Stephen J, et al. Acute and residual effects of marijuana: Profiles of plasma THC levels, physiological, subjective, and performance measures. Pharmacology Biochemistry and Behaviour. 1990;37(3):561-565.