Workplace safety is a top priority, yet many employers still struggle with how to address substance use in a way that is practical, fair, and legally sound. The issue is often framed around impairment, but as I’ve discussed before, impairment is a subjective and emotionally charged term that does little to help workplaces make informed safety decisions.
What we’re really concerned about is safety risk — a far more actionable and relevant concept for workplace policies. However, determining safety risk isn’t always straightforward. Various biological, contextual, and situational factors make it difficult to apply a one-size-fits-all approach.
In this article, we’ll explore the factors contributing to the complexity of safety risk and why employers should be cautious about relying on outdated impairment-based models.
1. Biological Differences Make Safety Risk Unpredictable
Each person’s biological makeup plays a significant role in how they experience the effects of substances.
Metabolism & Tolerance: Individuals process tetrahydrocannabinol (THC), the psychoactive ingredient in cannabis, in vastly different ways. Our unique metabolisms, tolerance levels, and neurological function mean that some individuals may be significantly unsafe with low levels of THC, while others appear to remain functional.
The Challenge of Drug Testing: It is scientifically impossible to equate an inactive urine drug metabolite with any level of impairment or safety risk. Many employers make the mistake of assuming that a positive urine test result for cannabis indicates impairment at the time of testing — it does not.
Unlike alcohol, which is water-soluble and eliminated at a predictable rate (roughly one drink per hour), cannabis acts very differently. Cannabis is fat-soluble, meaning it attaches to fat cells in the brain and other parts of the body, where it can remain for days, weeks, or even months. This makes it extremely difficult to correlate drug presence with impairment, further reinforcing why safety risk — not impairment — should be the focus.
2. Context Matters: The Workplace Environment Plays a Role
A person’s level of risk isn’t determined by substance use alone — it is also shaped by their work environment.
Safety-Sensitive vs. Non-Safety-Sensitive Roles: Employees who use cannabis recreationally outside of work may not present a safety concern in an office job, but for those operating heavy machinery or working in high-risk environments, any level of impairment could be catastrophic.
Stress, Fatigue & Multitasking: Workplace conditions can amplify the effects of substances. Someone who might function normally in a relaxed setting could experience increased cognitive impairment when under stress, sleep-deprived, or required to multitask.
Cultural Norms & Attitudes: Since Canada legalized cannabis, attitudes toward its use have shifted dramatically. Many people now see cannabis use as low-risk because it is legal, whereas employers generally view any level of use as a safety risk. These differences in perception create challenges for workplace policy application.
These aspects highlight why one-size-fits-all policies don’t work. Each workplace must assess its specific risks rather than rely on outdated impairment models.
3. The Hidden Risk of Substance Combinations
Most workplace safety policies focus on single-substance use, but in reality, employees often use multiple substances — intentionally or unintentionally — which can significantly increase safety risk.
Cannabis & Alcohol: Even if someone isn’t over the legal alcohol limit, adding cannabis can intensify cognitive impairment beyond what either substance would cause alone.
Prescription & Over-the-counter Medications: Many common medications, including painkillers, sedatives, muscle relaxants, antidepressants, and antihistamines, can interact with other substances, leading to unpredictable effects on cognitive and motor functions.
Polydrug Use is Common: Many individuals use multiple substances regularly, further complicating the ability to assess safety risk based on a single test result.
This complexity makes assessing safety risk based on testing alone even more difficult because most workplaces do not test for these substances.
What This Means for Workplaces
Employers must shift away from impairment-based policies and adopt a risk-based approach that prioritizes observable behaviours, situational awareness, and education over outdated drug test results.
✅ Train supervisors to recognize signs of safety risk rather than depending on unreliable impairment assessments.
✅ Educate employees about how different substances (and combinations) can affect safety.
✅ Adopt evidence-based testing methods, such as lab-based oral fluid testing, which is the only legally defensible test for detecting recent cannabis use.
✅ Promote a culture that focuses on health and safety, supporting employees rather than simply policing them.
By changing the conversation from impairment to safety risk, organizations can create fair, effective, and legally sound workplace policies that protect employees while maintaining a safe and productive work environment.
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