By Dr. Melissa Snider-Adler, Addiction Medicine Physician & Medical Review Officer
The legalization and normalization of cannabis across North America has created a new landscape for employers, particularly those operating in safety-sensitive environments. Cannabis is used widely, accepted widely, and misunderstood widely – and workplaces increasingly feel the effects.
One of the most common questions non-DOT employers struggle with is: “How long should employees refrain from cannabis use before performing safety-sensitive work?”
It’s a reasonable question with a complex answer.
Scientific evidence confirms cannabis can impair attention, judgment, reaction time, motor coordination, and complex decision-making. For some individuals, these effects resolve within several hours, depending on the route of administration.
For others – especially those with daily or chronic cannabis use, those using high-potency products, or individuals with early onset of use – residual impairment may persist well beyond 12 hours, into the next day or longer. Some studies show residual effects resolving days to weeks after abstinence.
It is important to acknowledge that real-world patterns of use (including concentrates, distillates, dabs, and products with extremely high THC levels) often are not reflected in clinical studies, making the true duration of impairment uncertain for many workers.
Why zero tolerance or 28 days is the standard for high-risk work
Some agencies and high-risk sectors adopt conservative approaches by implementing zero-tolerance cannabis policies or 28-day abstinence requirements. This approach is consistent with the National Safety Council’s Alcohol, Drugs and Impairment Division (NSC-ADID) and the American College of Occupational and Environmental Medicine (ACOEM) Guidance for Safety-Critical Workers.
If a workplace must ensure all employees are free from any psychoactive or residual effects of cannabis, a 28-day or zero-tolerance policy is the only way to meet that expectation.
However, not all workplaces operate under the same constraints.
While safety should be the priority always, many employers face competing factors, including legalization, state laws, human rights considerations, collective agreements or workforce realities.
In these contexts, some workplaces adopt alternative approaches, such as:
- 24-hour abstinence from cannabis before duty, or
- policies focusing solely on acute intoxication (generally within approximately 12 hours), often paired with oral fluid testing. These approaches carry different levels of risk and may or may not align with the hazard level of the work being performed.
Evidence matters. So does context
The appropriate timeframe between cannabis use and work depends on:
- the severity of operational and safety risk;
- the nature and complexity of the duties;
- whether roles are safety-sensitive or decision-critical;
- regulatory or contractual requirements;
- the organization’s tolerance for potential acute or residual impairment.
A high-hazard environment may require a zero-tolerance approach.
A moderate-risk workplace may reasonably choose 24 hours.
Other employers may rely on testing that identifies only recent use.
What matters most is that employers make decisions that are informed, defensible, and aligned with their operational needs and safety obligations. But even the strongest, most carefully designed policy means little if employees expected to follow it don’t understand it.
Policies set expectations. Education makes them work
In my work as an Addiction Medicine physician and MRO, I consistently see a major gap: many employees simply do not understand how cannabis affects their brain or why their workplace has adopted specific expectations.
Common misunderstandings include:
- “I don’t feel high anymore, so I must not be impaired.”
- “Cannabis is legal now. Why does my workplace still care?”
- “Edibles don’t affect me the same way, so the rules shouldn’t apply.”
- “If THC stays in your system for weeks, how can impairment only last hours?”
Without proper education, policies become documents employees sign, not rules they follow. Education bridges that gap by helping employees understand:
- why the policy exists;
- what the real risks are;
- how potency, frequency, and method of use influence impairment;
- what the expectations and consequences are;
- how to access help when substance use becomes a concern.
When workers understand the “why,” they are far more likely to follow the “what.”
Policy + education = A safer workplace
Cannabis in the workplace is not a temporary issue. It is an evolving reality. With the right combination of informed policy and effective education, employers can create safer, more consistent, and more supportive environments for their workforce.
For workplaces seeking more information about cannabis risks and policy considerations, I have created a free resource – “A Practical Guide to Cannabis Use & Workplace Safety” – that includes easy-to-understand, scientifically based information on cannabis use and a practical decision tree to support policy development.
You can download it at www.ffdlearning.com.
To learn more about the Alcohol and Substance Awareness Program (ASAP) designed to help employees understand workplace expectations and the risks of substance use, visit FFD Learning Inc.
Most workplaces have policies. Few have a workforce that truly understands them.