One of the policies which the new Victorian Government took to the election was a plan to legalise medical marijuana. That plan throws up, for Australian employers, a problem with which American employers have been grappling for some time; namely, how do you make a workplace drug testing policy work when an employee’s positive test for marijuana may be a direct (and lawful) result of treatment for the employee’s disability?

Our American cousins have had a little bit of time to think about this issue. There are now some 30 American states which permit, at least to some extent, marijuana use on medical grounds.  There, as here, workplace drug testing is increasingly common; there, as here, there are issues of workplace safety, employee privacy, and protection from disability discrimination which need to be considered. It’s not so much a question of being between a rock and a hard place as it is about being between a hard place and the stoned.

The particular problem with cannabis is that a “positive test” does not necessarily indicate impairment. With most other legal and illegal drugs, a positive result is usually a pretty good indicator that the person tested is affected by the drug. Take alcohol, for example – if a driver blows 0.08, the person’s functioning will be affected, and that is so whether or not the person feels drunk, and whether the 0.08 comes after a (slightly-too) long lunch or first thing in the morning after a big night.

THC, which is the active ingredient in cannabis, is fat-soluble, which means that it can be found in body fat deposits long after the last smoke has been inhaled (or not inhaled, if you’re Bill Clinton). Some literature suggests that if you are a heavy user of marijuana and you are also very fat, you can still test positive on a urine test up to three months after you have last consumed cannabis. Saliva testing has a shorter lag period, although you can still fail a test 48 hours after consumption. The pharmacological effect of marijuana is gone within 8-10 hours, so that equals a lot of positive tests which don’t equal evidence of impairment.

This issue creates problems for some employers at the moment, but at least the employer can say: “Well, if employees don’t want to get into trouble, maybe they shouldn’t break the law”. Medical marijuana changes all that, because the employee’s marijuana use becomes not just legal, but also a direct result of a medical condition which is likely to be a disability. Obviously, the fact that marijuana is prescribed does not mean that people are entitled to come to work baked (any more than they are entitled to come to work impaired by any other prescription drug). But what do you do with the positive tests which don’t demonstrate impairment?

Some US lawyers suggest that employees who are subject to random drug testing, and who are using medical marijuana, should disclose these matters to their employer. The problem with that is there are a number of medical conditions for which medical marijuana may be prescribed (for example, HIV/AIDS and various psychological conditions) which employees may well not wish to disclose. If the condition is not relevant to the employee’s ability to perform the inherent requirements of the position, a requirement to disclose may itself be an unlawful request for information.

Can an employer say that regardless of impairment, the ability to pass a random drug test is, of itself, an inherent requirement of a position? That may be tricky unless there is a compelling safety argument. You might not want to work in an office full of stoners (you’d need a dedicated budget line item for Tim-Tams, and the office stereo would be always playing The Grateful Dead, Bob Marley, Cypress Hill or whatever music Millennial weed fiends listen to). But if employees are performing, and you don’t have the safety issues of, say, a mine site, then it’s not obvious that being able to pass a test could or should be an inherent requirement.

That’s not to make light of the need for employers to consider whether drug testing is a necessary part of a particular workplace, but the impact of legalised medical marijuana is that there is another issue for employers to weigh up. Get it wrong, and you might find yourself suffering a case of joint liability.