Most US employers naturally have little tolerance for employees’ arriving to work under the influence of any illegal drug, including marijuana. Many Arizona employers have drug and alcohol testing policies which absolutely prohibit being at work possessing or being under the influence of marijuana and will often summarily terminate the employment of a marijuana-using violator. However, a new Arizona law will cause employers’ plans to terminate any employee who tests positive for marijuana to go up in smoke.

In November 2010, Arizona voters passed by a slim margin Proposition 203, Arizona’s medical marijuana law. The new law allows physicians to prescribe to registered patients small amounts of marijuana in order to treat certain debilitating medical conditions. The law further prohibits an employer from discriminating against an employee or applicant based upon the individual’s being a medical marijuana cardholder or for testing positive for marijuana. The law does not prohibit taking action against the employee if he or she was uses marijuana on the job or is impaired by marijuana on the employer’s property or while on duty.

However, the word “impaired” is the source of the confusion—and consternation. The law provides no guidance as to what “impaired” means or how employers are supposed to determine if an employee has been “impaired” as a result of marijuana. Although the state’s Department of Health Services is required to adopt implementing regulations relating to medical marijuana, the regulations proposed in January of this year provide no guidance on the topic either.

While Arizona employers are somewhat mystified by the new law, many wisely are in the process of updating their drug testing policies to account for the situation involving a medical marijuana cardholder and are educating managers concerning the issue, including training managers on how to detect signs of impairment which could be caused by marijuana. The next question: will Arizona managers begin conducting field sobriety tests? Stay tuned.