When states first began legalizing medical marijuana in the mid-to late 1990s, not many people would have guessed that in fewerthan 20 years, the substance would be decriminalized in 16 states,fully legal for adult use in two and approved for medical use in22.

There's a lot of overlap among those states, but between thestates with decriminalization statutes on the books and those thathave legalized marijuana for medical use, more than half of thestates in the country have enacted laws that somewhat or fullyprotect adults who use marijuana.

With this political sea change have come new challenges, notjust for dispensary owners and marijuana advocates, but foreveryone who owns a business in those states. Until the federal lawis changed, employers in states that allow some form of marijuanause are caught in the unique legal limbo that's created when statelaw allows something and federal law prohibits it.