This is a more nebulous issue in Massachusetts. Attitudes are changing toward medical marijuana use in the US, so this will hopefully be a moot point soon, but for now, this really depends on your employer. If you work for a federal employer that is following federal statutes for a drug free workplace, Massachusetts can't interfere with this and you'll have to follow your employer's drug policy. If you work for a private or state employer and you're fired for medical cannabis use, you do have the right to sue thanks to a landmark case in the state called Barbuto v. Advantage Sales and Marketing, LLC. This doesn't guarantee you'll win, but the court ruled that "the use and possession of medically prescribed marijuana by a qualifying patient is as lawful as the use and possession of any other prescribed medication.” Call your attorney to learn more if you think you've been discriminated against for off-the-job medical cannabis use. No employer in the state is required to allow on-the-job cannabis use.