Despite statutes and requirements in some states regulating the use of medical marijuana and its relation to the workplace, most states have preserved the employer's right to establish a drug-free work environment.   

With more states expected to decriminalize or otherwise legalize the use of marijuana for medical or recreational purposes, employers should consider reviewing policies to ensue compliance with local and state laws.

Another employment practice that comes into question is the conduction of drug tests, especially since employers may expect more challenges from employees who have failed drug tests, or claim that they were not impaired while on the job. While employers may be cautious about making changes that reduce the safety of employees, they must also come to acknowledge that workers using marijuana on their own time is not illegal. Employers may increasingly shift from testing for the presence of marijuana in an employee's system to one that measures an individual's impairment while on the job.

An upcoming case in the Colorado Supreme Court could also set a precedent across the country, as a former DISH Network telephone support operator Brandon Coats was fired from the cable company in 2010 for violating DISH's zero-tolerance policy after he tested positively for marijuana usage. Coats, a quadriplegic and medical marijuana patient, sued the company, arguing that he uses medical marijuana were in his own home and on his own time, and the use of the drug has had no impact on his work. While the Colorado Court of Appeals ruled against Coats, deciding that DISH Network has the right to enforce a drug-free policy, Coats has appealed the decision.  A ruling is likely to come from the state's Supreme Court later this summer.

Courts in California, Montana, Washington and Oregon have heard similar cases, but have ruled in favor of the employers. Judges consistently have said that medical cannabis laws protect patients only from criminal penalties, but not from termination by their employers.

In Colorado, Amendment 20 states that employers are not required to accommodate the use of medical marijuana in any workplace, but the law does not explicitly state whether the use of cannabis at home gives an employer the right to fire an employee. Regardless of the result of the final ruling, the decision will remove the law's gray area. Should the Colorado Supreme Court rule in Coats' favor, however, the decision will protect more than 110,000 registered medical marijuana users in the state. The precedent could eventually affect millions of employees across the nation.

Considering more than 40% of Americans ages 12 or older report having used cannabis in their lifetime, and more states are legalizing the use of the drug for medical—or recreational—purposes, employers must know their rights, but also consider evolving employment policies to promote the safety and productivity of the work environment while complying with state regulations. All employers with drug-free policies should do their research, perhaps seek legal counsel and ensure that their drug policies are enforceable, but also minimize risk and interruption to their business practices.