At this writing, many states have legalized medical marijuana and some of those have also legalized it for recreational use. This has caused confusion for both employers and employees when it comes to drug testing in the workplace. It has also led to some companies rethinking their policies on cannabis.

A survey conducted by the Pew Research Center in October 2017 found 61 percent of Americans support legalizing cannabis. And while it remains illegal under federal law, the...