Workplace drug screening firm The Drug Detection Agency says a rise in medical cannabis use is behind increased rates of tests showing up as positive for cannabis, a serious headache for employers and employees.

Medical cannabis is prescribed by doctors, but the company, as well as medical experts and employment lawyers, say showing up to a safety sensitive workplace with an active script doesn’t always cut it.

The products can either include psychoactive chemicals such as THC (the chemical in cannabis responsible for the associated high) or CBD (which doesn’t produce a high).

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Since 2020 cannabis could be prescribed to treat or ease conditions ranging from epilepsy, multiple sclerosis and cancer through to anxiety or sleep disorders.

While products have been available for a couple of years now, the company attributes the gap between 2020 and 2023 detection rates to regulatory pressures, and now believes the situation is at a tipping point.

Speaking at a seminar on the issue yesterday, The Drug Detection Agency chief technical officer Rod Dale said from a health and safety standpoint, legally acquired cannabis products were still a real issue.

Many cannabis medicines are used on an as-needed basis, but unlike some other impairing prescription drugs, THC can show up in a patient’s system for weeks after use.

No pinpoint

The company said tests couldn’t pinpoint when the products had been used and even if an employee had a prescription, the test would, for health and safety purposes, be considered a fail.

Medical review officer Dr Mary Obele, who assesses drug tests and follows up with employees, said it was far too complex to pinpoint firm details.

“No toxicologist, no forensic scientist, nobody can do that and absolutely guarantee it’s safe.”

The Drug Detection Agency and other drug testing firms don’t test for CBD, but Dale said there was evidence that some CBD products could trigger a positive result, and a number of employees had argued this line.

The company’s chief executive, Glenn Dobson, said business leaders need to understand, mitigate and address the issue immediately.

“We’re seeing cannabis trigger our testing devices regularly, which isn’t particularly new. What is new is that people in safety-sensitive workplaces then show up with a prescription for cannabis. But just because the substance is legal doesn’t mean it’s safe to take it and get behind the wheel of a 40-tonne truck,” Dobson said.

Drug testing is relatively common in workplaces that involve heavy machinery, such as transport, forestry, horticulture and in some trade roles.

The case against

Though few people would advocate for getting behind the wheel of a combine harvester stoned or drunk, drug testing does have its critics.

The NZ Drug Foundation believes though random drug testing can reduce employee drug use, it does not reduce near-misses, accidents or deaths in the workplace, because it detects previous use of drugs, not actual impairment.

Unlike alcohol breath tests, there isn’t an accepted form of impairment test for cannabis.

Medical Cannabis Council executive director Sally King believes a workplace ban on cannabis medicines is not a proportionate response to the risks they pose, “It is essential to understand that evidence of cannabis consumption is not evidence of impairment.”

King said it was working on resources to take to insurers, workplace health and safety bodies and public officials, “Establishing an appropriate response, creating a supportive workplace environment rather than one of stigmatisation and potential discrimination is very much needed in Aotearoa/New Zealand.”

Workplace drug testing isn’t mandated by WorkSafe, but it says drug testing may be a useful and proportionate tool for high-risk workplaces. It says if a worker is impaired or suspected to be impaired by alcohol or illegal drugs, they should not be allowed to work.

Employment New Zealand says drug and alcohol policies and processes are often more effective when they are mainly focused on prevention and protection rather than punishment.

Employment law

LangtonHudsonButcher partner and employment lawyer Andrew Schirnack, who presented alongside The Drug Detection Agency, said employees who were suffering from a condition and had been prescribed medicinal cannabis would hope most employers would look through a sympathetic lens.

Schirnack said the employer or manager then had to consider whether there was a risk of impairment and whether the employee could safely perform the requirements of their job.

He said the health and safety obligation had to be balanced with the duty to not discriminate against an employee because of a disability or impose on them an unreasonable requirement they cannot handle.

This means employers must consider whether reasonable adjustments are available.

What that might look like when it comes to cannabis is yet to be tested.

Schirnack suggested it could mean removing driving from an employee’s role if it made up a minor part of what they do.

If other work couldn’t be found to make up the time, a contractor with fewer hours might be offered, and if no options could be worked out, Schirnack said dismissal could be an option.

Andrew Bevin is an Auckland-based business reporter who covers major industries, markets, regulation, aged care and fisheries.

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