Recreational use of cannabis (i.e., marijuana) is now legal in Canada, nine U.S. states and the District of Columbia. Cannabis is also legal for medical use across Canada, in 31 states and in the District of Columbia. A patchwork of laws allowing varying levels of possession and use are being enacted at the province or state levels, making it difficult to know what’s allowed in the workplace and your community.

Cannabis use presents a workplace safety concern because, just like other drugs and alcohol, it can cause impairment. But, unlike other drugs and alcohol, there is no clear measure of cannabis-caused impairment. Employers are faced with managing these safety concerns while the legal landscape around cannabis use is still evolving.

One way to think about cannabis in the workplace is to think about how alcohol use, impairment and dependence are handled. There are a lot of similarities and a few key differences. Both alcohol and cannabis use are legal and socially acceptable, and yet they can also be prohibited in the workplace.

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Effects of Cannabis Use

Cannabis can be used for either recreational or medical purposes. THC (Tetrahydrocannabinol) is the chemical in cannabis that causes its psychoactive effects, commonly referred to as the “high.” Medical cannabis generally has the THC removed or minimized.

When THC is present, cannabis use can produce some or all of the following effects:

  • Dizziness, drowsiness, feeling faint, fatigue
  • Impaired memory
  • Disturbed attention, concentration and/or ability to make decisions
  • Disorientation, confusion, feelings of unreality
  • Nervousness, anxiety, hallucinations
  • Impaired motor skills and perception

The effects of cannabis use can vary widely depending on a number of factors. Was the cannabis inhaled, ingested, or applied topically? Is the person a firs- time or occasional user, or a long-time or chronic user? What concentration of THC was present? Was the cannabis consumed along with alcohol or some other drug?

  • With inhalation (i.e., smoking), effects may be felt within a few minutes and will generally peak within 30 minutes. Acute effects generally last 2-4 hours, but can be present for up to 24 hours.
  • With oral ingestion (i.e., eating) effects can begin as quickly as 30 minutes or as late as 3-4 hours later. Acute effects generally peak 3-4 hours later, but can last 8-24 hours.
  • With topical application (i.e., using a cream) the timing of the effects is unknown.

Safety Concerns Around Cannabis at Work

With the identified psychoactive and physical effects of cannabis use, the most obvious workplace safety concern is with driving vehicles and operating heavy machinery. Driving while distracted can easily cause accidents, and operating machinery while drowsy and under the effects of a substance could lead to disaster.

Less obvious are the safety concerns that come with inattentive or uncoordinated employees. Mistakes are made. Details are missed. Quality suffers. And, impaired employees can put themselves, their coworkers, and even customers in harm's way - regardless of whether they are in traditional safety-sensitive positions or not.

Determining Impairment from Cannabis

A number of factors make it difficult to determine whether a person is impaired due to cannabis use.

First of all, cannabis affects each person differently. A combination of how the cannabis is taken, THC strength, and if the person is habituated to cannabis all influence its effect on that individual.

In those places where cannabis is legal for medical use, that fact needs to be taken into consideration in determining workplace impairment. Medical use of cannabis, in these circumstances, can provide the employee with certain protections. Therefore, a distinction needs to be made between medical and recreational use and its impact on the job.

The effects of cannabis use can be altered when taken with a second drug. Intoxication is stronger when cannabis is taken with alcohol, opioids, or muscle relaxants. If it’s suspected that the employee is under the influence of more than one drug, that fact needs to be taken into consideration when testing for drugs and/or preparing a disciplinary action.

THC can stay in a person’s system for days, weeks, or months after use. The NHS found that urine samples from an occasional or first time user still tested positive up to four days after their last use. For frequent users, positive results were found up to 10 days after last use. And, for very heavy users, a positive result can be found up to two months after last use. While the presence of THC indicates cannabis use, it may not reflect the person’s current state or impairment.

Unlike alcohol, there is no single, agreed-upon or legislated THC level that constitutes intoxication or impairment. Some locations where recreational cannabis is legal have established specific thresholds to determine impairment while operating a vehicle. But, these places are the exception, and the threshold levels vary by location.

So, while an employer can include testing for the presence of THC as part of their drug testing program, the test results alone probably won’t establish whether the employee is impaired while on the job.

Observing and documenting the employee’s actions and behaviors while on the job are also needed to establish impairment. The employer’s response to these three key questions will help determine whether they believe the employee is impaired while on the job:

  • Can the person perform the job or task safely?
  • Is the person’s cognitive ability or judgement impacted in some way?
  • Are there any potential side effects of a medical condition or treatment that need to be considered?

Strategies that ensure workplace safety

A combination of clear workplace drug policies, consistent application of these policies by management and a strong workplace drug testing program are needed to effectively address the safety concerns that have come with legalized recreational cannabis use.

Here are a few key strategies for maintaining workplace safety to consider as cannabis use becomes legal:

  • Make sure your workplace drug and alcohol policies are up to date
  • Engage legal help to navigate the patchwork of cannabis laws that apply in your community and industry
  • Consider instituting a “no free accident” rule for safety-sensitive positions, requiring employees to disclose drug dependence up front and be offered treatment
  • Make treatment resources available to all employees who are experiencing problematic cannabis use
  • Train your managers and educate your employees about your workplace drug and alcohol policies and procedures
  • Make sure your employees understand what is and isn’t acceptable behavior and what the disciplinary consequences are when it comes to cannabis use and the workplace