Twenty states and the District of Columbia have passed a form of legislation that decriminalizes the use of marijuana for medical purposes, and Colorado and Washington have recently legalized the recreational use of the drug. While employers are under no legal obligation to allow marijuana use in the workplace, the drug's legality leads to questions regarding an employer's response to an employee who fails a drug test or admits to being a medical marijuana patient.

Marijuana possession and use remains illegal under the federal Controlled Substances Act, but federal enforcement is curtailed in states that have sanctioned the use of medical marijuana. In some of these states, laws prohibit discrimination against qualified patients in employment decisions.

Arizona, Connecticut, Delaware, Maine and Rhode Island employers cannot refuse to hire or penalize an individual based on his or her status as a marijuana patient. In Arizona and Delaware, particularly, a positive drug test alone will not provide an employer with sufficient grounds for discharge, unless the employee was in possession of the drug or was impaired while on the employer's premises or during work hours. Employers are expected to produce additional evidence of an employee being under the influence at work.