It is difficult to definitively quantify the effect marijuana use has on productivity and safety, but, according to the National Institute on Drug Abuse, part of the National Institutes of Health, studies have suggested links between marijuana use and negative consequences in the workplace, such as a higher risk for injury or accidents. 

Twenty-nine states currently have laws legalizing marijuana for medicinal purposes with an additional eight permitting recreational use of cannabis, including the District of Columbia.

For employers, a growing number of legal cases demonstrates the challenges with maintaining a safe, efficient workforce amidst the increasing number of states that have legalized medical and recreational marijuana.