Gina Tron is a freelance reporter and author of the memoir "You're Fine."

(AP Photo/Elaine Thompson, File)

Legal barriers to marijuana are falling all over the United States. Pot, tried by nearly half of all Americans at some point in their lives, is already legal in some form in 23 states, and four states allow recreational use. Last Friday, two House bills were filed that could end the federal prohibition of marijuana, including one which would remove marijuana from the Controlled Substances Act’s schedules and regulate it similarly to alcohol. And as of the early minutes of this morning, pot is legal in the District of Columbia.

Now there’s one thing that needs to disappear along with the prohibition of marijuana: employee drug testing.

Privacy arguments aside—should employers really be in the business of demanding body fluids from their workers?—this testing is expensive and does not effectively screen for good employees. In fact, it probably doesn’t effectively screen for drug users. Yet companies continue to drug test potential employees, even in states where medical marijuana is legal.

Even back in 1999, when pot legalization was nothing more than a pipe dream, an ACLU study concluded that drug tests were overly expensive and a poor indicator of workplace performance because they don’t test for impairments. Drug tests search for drug metabolites, which are by-products excreted from the body after a drug has been ingested. This means tests might catch a person who used an illicit substance in the recent past but probably not a person who is under the influence during the taking of the test; it takes a few hours for drug metabolites to appear in urine. Tests are arguably more likely to catch occasional users than drug abusers. As the ACLU concluded, “If drug-related impairment on the job is an employer’s primary concern, drug testing is both an over-inclusive and an under-inclusive strategy.” The study also said that the most common “illicit drug users” were occasional marijuana users.

And most illegal drugs are less impairing than alcohol, which is not tested for by employers, as the National Academy of Science has noted. If anything, the Academy concluded from lab studies, moderate doses of stimulants and cocaine had “slight performance-enhancing effects.” The use of certain drugs may not even have a correlation with poor work performance. Companies with drug testing actually have lower productivity over ones that don’t, according to one study.

Even if an employer wanted to keep drug testing employees for substances other than marijuana, they are unlikely to catch them. Pot stays in the body the longest of any classified drug and can show up in urine tests weeks or months after its used. Cocaine can pass through the system in as little as one to three days, and meth can leave the body in one to five days, though this varies slightly depending on age and usage. If a worker binged on cocaine or meth and took a drug test a few days later, he or she might pass more easily than somebody who smoked a joint a few weeks ago.

Medical marijuana use among workers further illustrates how futile drug testing can be. People who are prescribed marijuana for a disability or injury can still be fired or denied employment if they test positive for THC, even in states where medical marijuana is legal. This often is the case with national companies who apply the same regulations in all the states in which they operate. In 2010, Dish Network fired customer service representative Brandon Coats after he tested positive for THC. Coats is a quadriplegic living in Colorado who is prescribed medical marijuana. Dish Network’s “zero-tolerance” drug policy doesn’t recognize medical marijuana, even though Colorado’s constitution has allowed the use of cannabis with written medical consent since 2000. (Interestingly, some companies that ban pot will allow medically prescribed Oxycontin, at one point the poster child for prescription pill abuse in the United States.)

Screening for pot was never good policy for employers. Continuing to do so as medical marijuana became legal made even less sense. Now that recreational use becomes more acceptable under the law, it’s downright illogical.