Drug testing employees is routine for many employers. It’s likely been the policy for as long as senior leadership can remember. And so, every time a new hire joins the company, they’re sent off to pee in a cup and prove they’re drug-free. A recent survey of around 70,000 working people across the U.S. found that 48.2 percent were getting screened for drugs by employers. This includes most Fortune 500 companies.

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But is there a good reason to test employees for drugs? All employers can agree they don’t want impaired employees on the job, but these tests haven’t proven to prevent that. A drug-screening policy is a costly one, too, especially for something that might not tell you what you want to know. So how did it get to be so popular?

Just Say No

The big break for drug tests happened in the 1980s after President Ronald Reagan signed an executive order for the heads of all federal agencies to put a drug testing program in place. He wanted a “drug-free federal workplace,” and he thought drug tests were the way to get there.

In 1988, Congress followed the president’s lead, mandating that companies with government contracts or grants maintain a “drug-free workplace.” 1991 saw another federal law requiring drug and alcohol testing for “safety-sensitive” employees in private transportation companies. By 1996, the majority of companies in the American Management Association — 80 percent — had some form of drug testing in place. Two-thirds of the businesses tested all new hires.

The Science

Drug testing may be the norm for most companies, and it seems clear why. Again, no one wants an employee at the office to be on drugs. But the science as far as how well drug screens actually test for that is nowhere to be found. The most common form of drug test — a urine sample — simply shows whether a drug has been used in the last few days or even weeks. Drug use off-the-clock has not been shown to prove on-the-job use.

There is also the issue of what the test is looking for. There are 17.3 million Americans that are dependent on alcohol, according to the National Institute on Drug Abuse. That’s double the number of people hooked on all other illicit drugs combined. Generally, the tests today are not screening for alcohol abuse, which can also lead to behavior that is unwanted in the workplace.

The Good News

Drug-testing is costly for employers, so it’s important to think about the science, but there are also benefits to the policy, as well. Simply having a drug-testing policy in place was proven — in a 1999 study — to act as a deterrent, with fewer employees self-reporting drug use when they were subject to drug tests. It can also help employers to know what kind of person they are hiring. Drug use around an application period could be an indication of lack of self-control. In addition, random drug testing can be valuable for employees who have high-risk positions, where a momentary lapse could mean life or death. This is especially true for pilots or train drivers. And drug testing may help companies control legal liability in the case of accidents.

Rather than relying on an old policy or simply testing because everyone else is doing it, smart employers will look at the pros and cons of drug-testing and make their own decisions. It might make sense for one company to keep the policy in place, while another company could save a lot of time and money by adjusting their policies.