Substance use, impairment and the workplace

Substance use and mental health are closely linked. Some people use alcohol, cannabis or other drugs to cope with stress, anxiety, trauma or sleep problems; substance use can also worsen mental health and lead to substance use disorders, which are themselves mental health conditions. At work, substance use raises safety concerns, because impairment can cause serious incidents, and it raises fairness and human rights concerns, because addiction is recognized as a disability. This lesson covers how to think about impairment broadly, how to respond supportively and fairly to substance use, and the laws on cannabis, testing and accommodation in each country.

Impairment has many causes

Impairment means a reduced ability to perform work safely and effectively. Alcohol and drugs are only some of the causes. Fatigue (Lesson 6), legally prescribed or over-the-counter medications, illness, acute stress, grief and trauma can all impair judgement, attention, coordination and reaction time. A sound workplace policy therefore focuses on fitness for work: every worker has a responsibility to arrive fit to work safely and to tell their supervisor if they are not, whatever the reason, and every supervisor has a responsibility to respond when they observe signs of impairment. This approach is fairer and more effective than one focused only on illegal drugs.

The spectrum of substance use

Substance use exists on a spectrum, much like the mental health continuum. Many people do not use a particular substance at all; many others use alcohol or cannabis occasionally and at low risk. Some use at levels or in situations that cause harm, such as drinking heavily the night before a safety-critical shift. A smaller number develop a substance use disorder, a diagnosable condition in which a person continues to use despite significant harm, often with cravings, loss of control and withdrawal symptoms. People can move along the spectrum in either direction, and recovery is common with support and treatment.

Canada's Guidance on Alcohol and Health, published by the Canadian Centre on Substance Use and Addiction in 2023, advises that the risk of harm rises with every additional drink, from low risk at two or fewer standard drinks a week to increasing risk at three to six and high risk above that. Canada's Lower-Risk Cannabis Use Guidelines advise, among other things, not using cannabis before driving or operating machinery and avoiding frequent use. Canada has also faced a severe toxic drug crisis since 2016. Data from several provinces show that a large share of people who died of toxic drug poisoning were employed, with workers in construction and the trades over-represented, so many employers now include opioid awareness and naloxone in their programs.

Work factors that contribute

Psychosocial hazards can contribute to harmful substance use. High stress, long or irregular hours, shift work that disrupts sleep, traumatic exposure, isolation, a culture of heavy drinking at work events, and physically demanding work that leads to chronic pain can all increase risk. A psychological health and safety program that reduces these hazards also helps prevent substance-related harm. Treating substance use only as a matter of individual discipline misses this connection.

Responding to suspected impairment

When a supervisor sees signs that a worker may be impaired, such as slurred speech, the smell of alcohol, unsteady movement, confusion, unusual behaviour or a near miss, the first priority is safety. A common sequence is:

• Remove the worker from safety-sensitive duties immediately and keep them in a safe place.
• Speak to them privately and respectfully, describing what you have observed, without accusing or diagnosing.
• Involve a second supervisor or manager as a witness where possible, and follow your organization's fitness-for-work procedure.
• Arrange safe transport home or to medical care; never let a possibly impaired worker drive.
• Document the observations factually: what you saw, heard and smelled, when, and what actions were taken.
• Follow up with HR, occupational health or disability management on next steps, which may include a fitness-for-work assessment, testing where lawful, accommodation or discipline.

Signs of impairment can also have medical causes, such as a diabetic emergency, stroke or reaction to a medication, so treat the situation as a possible medical emergency if the person seems seriously unwell, and call 911 if needed.

Medications and impairment

Many legal medications can affect alertness, coordination or judgement, including some antihistamines, sleep aids, opioid painkillers, muscle relaxants, some antidepressants and anti-anxiety medications, and medications that lower blood sugar. Starting a new medication, changing a dose or combining medications with alcohol can be especially risky. Workers in safety-sensitive roles should ask their doctor or pharmacist whether a medication could affect their ability to work safely and should tell their supervisor if it might, without needing to disclose the medication or the condition it treats. Supervisors should respond to such a disclosure as a safety and accommodation matter, for example by temporarily assigning other duties, not as a disciplinary issue. A policy that punishes people for disclosing medication effects simply encourages them to hide it.

Opioid overdose awareness

Because of the toxic drug crisis, many Canadian workplaces now train workers to recognize an opioid overdose and use naloxone, a medication that can temporarily reverse an opioid overdose. Since June 2023, Ontario's Occupational Health and Safety Act has required employers who become aware, or ought reasonably to be aware, that there may be a risk of a worker having an opioid overdose at a workplace to provide a naloxone kit, maintain it and ensure a trained worker is available. Signs of an opioid overdose include unresponsiveness, slow or stopped breathing, blue or grey lips and fingertips, very small pupils and gurgling or snoring sounds. The response is to call 911, give naloxone if available and trained, provide rescue breathing or CPR as trained, and stay with the person. The federal Good Samaritan Drug Overdose Act offers some legal protection to people who call for help at an overdose.

Overdose awareness also belongs in the wider psychological health and safety picture. Workers who lose a colleague to an overdose, or who respond to one at work, may be deeply affected and should be offered the same support as after any other critical event (Lesson 11). Talking about substance use without stigma, and making it clear that people who seek help will be supported, helps more people get help before a crisis.

Cannabis and the law

Non-medical cannabis has been legal for adults in Canada since October 17, 2018, under the Cannabis Act, with provinces and territories setting the minimum age, retail rules and where it can be used. Legalization did not change the rule that workers must not be impaired at work. OHS laws and employer policies can prohibit impairment and use at work, and safety-sensitive roles may have stricter rules, such as no use within a set period before a shift. Workers authorized to use cannabis for medical purposes are entitled to have accommodation considered, like any other medication, but an employer does not have to permit impairment in a safety-sensitive role and may accommodate through alternative duties or treatments. Because there is no reliable test that shows current cannabis impairment the way a breathalyser does for alcohol, policies usually rely on observed signs of impairment and on fitness-for-duty assessments.

Testing and human rights in Canada

Canada has no general law requiring or authorizing workplace drug and alcohol testing in the private sector. Instead, testing is shaped by human rights law, arbitration decisions and privacy law. Courts and arbitrators have generally accepted testing in safety-sensitive positions in specific circumstances: for reasonable cause, after a significant incident or near miss, and as part of a return-to-work or monitoring agreement after treatment. Random testing is much more restricted. In Communications, Energy and Paperworkers Union, Local 30 v. Irving Pulp and Paper (2013), the Supreme Court of Canada held that a unilaterally imposed random alcohol testing policy in a dangerous workplace was unreasonable without evidence of a significant problem with alcohol use in that workplace. Pre-employment drug testing is also restricted. Because substance dependence is a disability under human rights law, an employer that learns a worker has an addiction generally has a duty to accommodate, often by supporting treatment and return to work with monitoring, up to the point of undue hardship. In Stewart v. Elk Valley Coal (2017), the Supreme Court of Canada upheld the termination of a worker with an undisclosed cocaine dependence under a policy that offered no penalty to those who disclosed before an incident, finding that the termination was based on the policy breach rather than the addiction. Canadian truck drivers who cross into the US must meet US Department of Transportation testing rules.

A supportive approach

Whatever the legal framework, workplaces that combine clear safety rules with support tend to achieve better outcomes than those that rely on punishment alone. A supportive approach includes:

• A clear, well-communicated policy on fitness for work, covering alcohol, cannabis, other drugs, medications and fatigue.
• Training for supervisors in recognizing impairment and responding consistently and respectfully.
• Encouraging early self-disclosure, with assurance that workers who seek help before an incident will be supported.
• Access to the EAP, treatment and peer support, and recovery-friendly return-to-work plans with clear expectations and, where appropriate, monitoring.
• Avoiding a culture that centres social events on alcohol, and offering alternatives.
• Reducing work factors that contribute to harmful use, such as chronic stress, fatigue and untreated pain.