Cannabis may be legal in Canada, but that does not mean workers are permitted to be high on the job. Like alcohol, marijuana use during work hours is frowned upon or forbidden by many employers. In some cases, being high on the job also creates a health and safety risk (both to the individual and others in the workplace).
Despite these conventions, there are few situations in which employers in Canada are permitted to have a worker tested for marijuana use at work. As outlined in a brief by the Ontario Human Rights Commission, drug testing may be permissible as part of a post-incident investigation or a return-to-work rehabilitation plan; but even then, it’s restricted by the protections in place by human rights laws.
When it comes to marijuana or cannabis hair testing, it is even less likely that employers will be permitted to subject their employees to the test. This is because hair testing is not a feasible means of testing cannabis impairment.
Unlike urine or blood sample tests, hair tests can detect evidence of marijuana up to 90 days or longer after use, which is a far wider window of detecion than either of the fluid-based tests. Additionally, the amount of delta-0-tetrahydrocannabinol (THC) found in hair follicles does not increase when a person is high and then decrease as they come down. The amount of THC found in a hair sample can indicate whether the person is an infrequent or chronic user of marijuana, but not whether they are currently impaired.
As explained in an article published by Healthline, THC is temporarily stored in a user’s organs and fatty tissues, then broken down in the liver and disposed of in urine or stool. However, THC that finds its way into the kidneys can be reabsorbed into the bloodstream. From there, traces of THC can bind to the user’s growing hair follicles and find its way into the hair itself five to 10 days later.
During a hair testing, the lab technician collects a sample of approximately 1.5 inches of hair near the base of the scalp. Since most people’s hair grows at a rate of about half an inch per month, the hair sample can reveal evidence of marijuana use over approximately 90 days previous.
In our view, the only circumstance in which a Canadian employer may have grounds to demand marijuana or cannabis hair testing from an employee would be as part of a return-to-work rehabilitation plan. If employee agreed to abstain from cannabis completely for during the rehabilitation period, a hair test could be justified as a way of ensuring the agreement is being upheld. Hair testing may be preferable in that case as it is less invasive than blood or urine tests.
- As far as we know, there are no jobs in Canada that require a hair drug test to screen for marijuana use as a prerequisite for employment.
- Generally, employers are discouraged from subjected employees to drug tests of any kind and are only permitted to do so in certain situations. The only situation involving a hair test that might pass scrutiny would be testing as part of a return-to-work rehabilitation plan.
- Hair tests cannot demonstrate that a person is high.