Detecting Impairment in the Workplace

June 17, 2019

The legalization of cannabis has heightened concern and awareness around impairment in the workplace. Legalization has certainly made cannabis more accessible. However, it is still generally understood that it is inappropriate to report to work impaired unless an employee is part of an agreed accommodation arrangement where some level of impairment is permitted, or the employee works in a very special work environment.

Rest assured, the legalization of cannabis has changed nothing with respect to impairment in the workplace; occupational health and safety legislation continues to impose a joint obligation on employers and employees to ensure the safety of everyone at the workplace, and human rights law continues to require employers to accommodate individuals with illnesses or disabilities to the point of undue hardship, including individuals prescribed medical cannabis (or any other prescription drug).

Some employers may be concerned that legalization will increase instances of employee impairment at work. This concern may be justified, mostly because there is still uncertainty regarding the duration of any impairment caused by cannabis. A recent labour arbitration decision out of Newfoundland and Labrador highlights this. In Re Lower Churchill Transmission Construction Employers’ Assn. Inc. and IBEW, Local 1620 (Tizzard) (2018), 136 C.L.A.S. 26, the arbitrator referenced multiple medical authorities and concluded that (i) impairment could last for more than 24 hours after use, (ii) it was possible for an employee to be impaired and not know it, and (iii) there was simply no reliable way for the employer to know whether an employee was impaired. Due to this uncertainty, the arbitrator concluded that the employee, who worked in a safety-sensitive position and was prescribed medical cannabis, could not be accommodated. The arbitrator’s decision was upheld by the Newfoundland and Labrador Supreme Court.1

It is uncertain whether this case will result in similar decisions in other provinces. It likely won’t with respect to non-safety-sensitive positions, as the duty to accommodate individuals who are prescribed medication of any kind for illnesses is generally fairly stringent. What is certain, however, is that more studies are needed to better understand the effects of cannabis. In the meantime, employers and employees should educate themselves on what the typical signs of impairment are in order to ensure the safety of all in the workplace. This article’s focus is cannabis, but some of these tips could be modified to apply to almost any impairing substance.

Signs of Impairment

Common signs of cannabis impairment include abnormalities with respect to:

  • appearance (i.e., bloodshot eyes),
  • odour/smell (i.e., smell of cannabis),
  • behaviour (i.e., loud, inappropriate, easily angered, anxious, depressed or sullen),
  • coordination or motor control (i.e., unsteady gait, clumsiness, shaking or tremors),
  • speech (i.e., thick or slurred speech)
  • memory (i.e., trouble recalling recent events or difficulty concentrating), or
  • health (i.e., signs of physical illness, vomiting).

If any of these abnormalities are noted and inconsistent with an employee’s normal demeanour, it is likely appropriate to ask in private whether that person is impaired, or if there is some other reason why that person appears to be impaired. Advise that person that the primary concern is safety, then try some of these questions:

  • Have you used any form of cannabis in the past? If so, how often, how recent, and how much? (Recent use would indicate a greater likelihood of impairment. However, how cannabis is consumed affects how soon the effects kick in.)
  • How do you normally consume cannabis? (Research indicates that ingesting cannabis results in a delayed “high” that is less acute but lasts longer than smoking.)
  • Do you obtain cannabis from a trusted/legal source? (Legal producers must meet strict health and safety guidelines, and legal sources disclose THC levels in their cannabis – THC is the psychoactive ingredient in cannabis.)
  • Do you know the THC levels in your cannabis? (Higher THC relates to more acute impairing effects and some strains of cannabis may contain no THC.)
  • Do you take cannabis with any other substances? (Generally, when cannabis is used in conjunction with other impairing substances, less of each substance is required to become impaired.)

Common Testing Methods

Some workplace policies allow for drug testing in certain situations. The most common include post-accident testing and “reasonable grounds” testing (the above tips will assist in establishing whether there are reasonable grounds to test). As noted above, testing for impairment remains a tricky topic. However, certain tests have proven effective in detecting impairment, and new ways of detecting impairment continue to emerge.

Common methods of testing include urine, blood, hair, and saliva testing. Of these, saliva swabs tend to be the preferred means of testing when it comes to cannabis. This is because cannabis metabolites tend to disperse faster in the mouth than in other parts of the body. Thus, a positive saliva test indicates more recent use, which in turn indicates a greater likelihood of current impairment. THC can build up in the body depending on frequency of use and the THC concentration in the cannabis consumed. Blood, hair and urine tests can detect this build up, which calls into question whether a positive test is an indication of current impairment. However, positive blood, hair or urine tests can still provide evidence of impairment when coupled with observed signs of impairment and/or an accident or near-miss. Employers should set appropriate thresholds of what constitutes a positive test depending on the method of testing chosen. Be aware that the lower the threshold the less likely a positive test will indicate current impairment. A recent labour arbitration decision from British Columbia held that a positive urine test for the presence of cannabis only establishes past use, not current impairment (see Teck Coal Ltd. and USW, Local 7884, Re, [2018] B.C.C.A.A.A. No. 6, 134 C.L.A.S. 126 at paragraphs 376 and 378). The threshold for a positive test in this case was merely the presence of cannabis metabolites and the arbitrator struck down the employer’s testing policy. The legalization of cannabis has not changed an employer’s right to impose drug tests on employees. Tests that require taking blood or hair are considered highly invasive, and are more likely to run afoul of an individual’s privacy rights.

Some traditional sobriety tests have proven effective in detecting impairment due to cannabis. One study2 showed that 96.7 percent of individuals who recently consumed cannabis failed at least two of these tests:

  • A one-legged stand in which the driver counts down while holding one foot in the air;
  • Standing with eyes closed and estimating the passage of 30 seconds;
  • Touching the tip of the nose six times, three times with the index finger of each hand; and,
  • Taking a series of heel-to-toe steps in a prescribed way.

Newer technologies are also being used to detect impairment, and they do not rely on any bodily samples being taken. A smartphone app called “Druid”3 operates much like a field sobriety test that individuals can do on themselves. The Druid app test requires individuals to follow a dot on the screen of their smartphone with their finger. The app user starts by doing several tests while sober to set a standard. Later tests will be measured against that standard to indicate whether the user is impaired. The benefit of physical impairment tests, like the one in Druid, is that they can test for current impairment from just about any source—lack of sleep, medication, alcohol, cannabis, etc.

Lessons for Employers and Employees

These are exciting times for Canada, as we are in mostly uncharted waters. Canada has taken a large step towards eliminating the stigma attached to cannabis use, and many other nations are looking to follow suit. In a sense, the world is watching. While our understanding of the effects of cannabis continues to grow, we must set an example by promoting responsible use and keeping safety top of mind by recognizing the following key points:

  • The duration and intensity of cannabis impairment are based on a number of factors. Research has shown that:
    • Impairment can last for over 24 hours.
    • Consuming high quantities of cannabis and/or cannabis with high THC content (more than 10%) results in longer periods of impairment.
    • Ingesting cannabis results in a delayed high that lasts longer while smoking results in a more acute high that is shorter. Impairment will follow this pattern.
  • Cannabis should only be purchased from legal sources to ensure it meets health and safety standards.
  • If you consume cannabis recreationally, consider monitoring your consumption and conducting physical sobriety tests using available technology to understand how cannabis may affect you.
  • Know the signs of impairment so that you can help keep your workplace accident free.

Stay safe everybody!


1 International Brotherhood of Electrical Workers, Local 1620 v. Lower Churchill Transmission Construction Employers’ Association Inc., 2019 NLSC 48 (CanLII), online:

2 Patrick Cain, Simple roadside tests can identify pot-impaired drivers, study shows, Global News, online:

3 Druid App, online:

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Cox & Palmer publications are intended to provide information of a general nature only and not legal advice. The information presented is current to the date of publication and may be subject to change following the publication date.