The proliferation of different, sometimes conflicting laws and policies on marijuana use is especially vexing for companies operating across the globe – or even just in multiple states within the US.

In the US, marijuana is illegal under federal law, but 30 states and the District of Columbia have legalised it for medical or recreational purposes. More than 20% of American adults use marijuana and 14% do so regularly, according to a survey this year by Yahoo News and Marist College in Poughkeepsie, New York. And marijuana use is expected to jump significantly over the next few years in North America. Voters in California, by far the largest state with nearly 40 million residents, legalised recreational marijuana last November. Meanwhile, Canada is poised to legalise cannabis for recreational purposes next year. (Both California and Canada long ago legalised the drug for medical treatment.)

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Marijuana use, however, is still illegal in many countries, including the UK, France, Ireland, Indonesia, China, Japan, South Korea and Saudi Arabia. But personal use in varying quantities has been decriminalised in such countries as Italy, Mexico, Argentina, Austria, Chile, Colombia, the Netherlands, Spain and Switzerland, while medical use of the drug is legal in many countries, including Australia, the Czech Republic, Germany and Turkey. Uruguay became the first country to fully legalize the production and sale of recreational marijuana. Pharmacies began selling the drug there this month.

“You almost need counsel in each country you operate in so that you set up a workplace drug policy that won’t violate that country’s laws,” says Tony Fiore, a lawyer at Kegler Brown Hill & Ritter in Ohio.

Patchwork laws

Some US laws and court rulings permit companies to arbitrarily fire employees who test positive for marijuana in states where it’s now legal. For example, the Colorado Supreme Court has ruled that employers can fire workers who test positive for cannabis even when they’re using if for medical reasons. Because marijuana remains illegal under federal law, the court upheld the firing of Brandon Coats, a quadriplegic telephone customer service representative at Dish Network who was using the drug to treat painful muscle spasms and tested positive in a random test.