The movement to normalize the use of marijuana is growing  across the United States.  Nearly half of states now allow medical use of marijuana and, in November 2012, Colorado and Washington became the first places in the world to pass legislation legalizing the regulated production, sale and recreational use of marijuana.

Now this movement is turning its sights on employer drug testing, arguing that, in an environment that is increasingly tolerant of marijuana use, testing for marijuana is outdated, irrelevant and, in some cases, even illegal. In Colorado, a medical marijuana user is suing Dish Network for firing him over a positive drug test, bringing the legality of such screening into question. Meanwhile, marijuana advocates are targeting drug-testing policies of major employers, including launching a petition to pressure the New York Times to trash its drug-testing policy. If successful, this movement will damage the safety and productivity of U.S. workplaces and take away one proven way to reduce substance abuse.

Workplace drug testing became commonplace in the 1980s as employers sought to reduce the negative effects of drug use. This practice has succeeded. After implementing drug testing programs, many employers have reported higher productivity, less absenteeism, lower employee turnover, and declines in workers’ compensation claims. In a 2011 poll of human resources managers, the number of employers reporting high absenteeism fell by half after implementing drug-testing programs. Nearly one in five reported improved productivity.

Further, employers are legally obligated to provide safe and healthy environments for their employees. Drug testing is a crucial part of achieving that goal. Post-accident testing helps identify the use of impairing substances, including marijuana, that causes accidents and injuries on the job. There is clear evidence of the short- and long-term adverse effects of marijuana use, including impairment related to memory, altered judgment, motor coordination, cognition, and even addiction. In chronic daily marijuana users, impairment in critical tracking and divided attention tasks are observed following three weeks of abstinence. For all of these reasons, marijuana and other illicit drug use is prohibited by many employers, including specifically under federal regulations for commercial drivers, airline pilots and train engineers. These issues are particularly important to safety sensitive roles, but substance abuse adversely affects all workplaces. The legalization of marijuana for medical and recreational use does not change these facts.

It is uncommon for an occasional user to be identified in random workplace drug testing. An analysis that I conducted showed that, in random workplace drug tests, about 52 percent of all positives will be daily drug users, 41 percent will be monthly drug users and only 7 percent will be annual drug users.  While it is true that marijuana metabolites are retained in the body longer than alcohol and most other drugs, about 40 percent of people who smoke one or two marijuana joints at night test negative the next day and nearly all will test negative within five days. In contrast to an occasional smoker, marijuana can be detected in the urine of chronic smokers for several weeks after they stop smoking. Employer drug testing is an important tool in reducing drug abuse problems nationwide. Over 6.3 million Americans age 18 and older have an illicit substance use disorder and the large majority of these individuals are employed either full or part time. Employer drug testing helps identify Americans who need help curbing their dependence or chronic use and, in many cases, provides or directs them to treatment.

Some marijuana advocates argue that companies conducting drug tests in states that have legalized marijuana are at odds with the law. That’s not true. Marijuana sale and use remain illegal under federal law everywhere in the country. Federal law supersedes state law when they conflict. That being said, it is wise for employers to update their drug testing policies and procedures in the states with medical and/or recreational marijuana so that expectations for employees are clear.

Changes in state marijuana laws do not invalidate the accomplishments made over the last three decades to establish drug-free workplaces, improving workplace safety and employee health. While it’s true that drug testing has declined in recent years in an effort to cut business costs, more than half of employers in the U.S. continue to drug test their job candidates. That’s because these programs benefit both businesses and society. Stopping workplace drug testing for marijuana and other drugs of abuse would negatively affect the productivity and safety of the U.S. workforce.

Note: This author’s bio has been updated to reflect his interest in a company that provides drug testing and employee assistance programs.