Emerging Issues Bulletin #6 | Drug Offences in Canada

Emerging Issues Bulletin: Issue # 6



Bruce A. MacFarlane, Robert J. Frater, Croft Michaelson


The Emerging Issues Bulletin in Drug Offences in Canada, 4th edition is intended to provide updates on notable drug policy, legislative and enforcement issues. These are issues that may have started to be addressed in case law in trial courts, or reflected in legislation just passed or being contemplated, or concerning new enforcement techniques by the police. By focusing on percolating issues, it is hoped that the section may alert practitioners to emerging legal challenges.

A sample from the most recent Bulletin is excerpted here. To continue reading from Drug Offences in Canada, 4th edition, sign up at the bottom of the screen for a free 14-day trial of CriminalSource on WestlawNext Canada.


Cannabis Impaired Driving

One of the biggest challenges for jurisdictions that have legalized cannabis is dealing with drivers who may be impaired by cannabis consumption. What levels of ingestion are impairing, and how to accurately test levels of impairment, are ongoing challenges. They are very significant ones: in Colorado, a recent investigation by the Denver Post found that the number of drivers involved in fatal accidents who tested positive for cannabis has risen sharply every year since 2013, more than doubling in that time.[1]

A recent report prepared for the U.S. Congress by the National Highway Traffic Safety Administration has examined the issues in detail, and contains some troubling findings.[2] The Report contrasts alcohol testing for impairment, which is based on 60 years of scientific studies, with more recent attempts to draw the link between cannabis consumption and impairment. The authors state that:

. . . alcohol is a relatively simple drug whose absorption, distribution and elimination from the body along with the behavioral and cognitive effects are fairly well documented. In comparison, the absorption, distribution and elimination from the body of marijuana (and many other drugs), along with the behavioral and cognitive effects is very different from the case with alcohol. [At p. 4.]

One of the key findings in the report concerns the correlation between blood levels of THC, the psychoactive component in cannabis, and driving impairment. The authors note that the correlation is not the same as for alcohol:

While fewer studies have examined the relationship between THC blood levels and degree of impairment, in those studies that have been conducted the consistent finding is that the level of THC in the blood and the degree of impairment do not appear to be closely related. Peak impairment does not occur when THC concentration in the blood is at or near peak levels. Peak THC level can occur when low impairment is measured, and high impairment can be measured when THC level is low. Thus, in contrast to the situation with alcohol, someone can show little or no impairment at a THC level at which someone else may show a greater degree of impairment. [At p. 7.]


Existing studies demonstrate that use of cannabis adversely affects drivers' reaction times and attention maintenance, but testing to determine the exact impact remains challenging. Development of reliable screening machines remains a work-in-progress. As well, studies show that many drivers use cannabis in combination with alcohol, so the compounding effects require study. The authors seem skeptical about the feasibility of developing a chemical test for cannabis impairment, because "[w]hile very high levels of THC do indicate recent consumption (by smoking marijuana) it is very unlikely a police officer would encounter a suspect and obtain a sample of blood or oral fluid within a short enough time for high THC levels to be detected" (at p. 13).

The Report offers three recommendations to attempt to find lasting solutions to the problems of cannabis impaired driving. The authors recommend that more police officers be trained as Drug Recognition Experts, the existing strategy for detecting drug impaired driving, that research into detection devices be continued, and that data collection efforts on the prevalence of cannabis use among drivers, particularly alcohol impaired drivers, be encouraged.

[1] D. Migoya, "Exclusive: Traffic fatalities linked to marijuana are up sharply in Colorado. Is legalization to blame?", Denver Post, August 25, 2017. In 2013, 47 people tested positive, and in 2016, 115 did.

[2] National Highway Traffic Safety Administration, "Marijuana Impaired Driving: A Report to Congress", July 2017.
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