The legalization of marijuana in nine states and Washington, D.C., has been the subject of intense controversy.

A new report further shows that policies liberalizing the legal use of “recreational drugs” are not without adverse side effects.

A study conducted by Quest Diagnostics, which runs blood-testing laboratories nationwide, shows that drug legalization in several states has brought a surge in workers using controlled substances.

As the study points out, “Overall, marijuana positivity continued its five-year upward trajectory in urine testing for both the general U.S. workforce and the federally mandated, safety-sensitive workforce. Marijuana positivity increased 4 percent in the general U.S. workforce … and nearly 8 percent in the safety-sensitive workforce.”

Such safety-sensitive professions include nuclear power plant workers, air traffic controllers, and airplane pilots.

“These increases are similar to the increases we observed after recreational marijuana use statutes were passed in Washington and Colorado,” said Dr. Barry Sample, a technical supervisor at Quest Diagnostics.

“While it is too early to tell if this is a trend,” he continued, “our data suggests that the recreational use of marijuana is spilling into the workforce, including among individuals most responsible for keeping our communities safe.”

Sample added: “We encourage policy analysts to track these trends closely to determine whether a correlation between the state legalization of marijuana and increased workforce drug use, as suggested by our data, bears out in other research.”

Smart Approaches to Marijuana (SAM), which is based in Washington, D.C., released a statement on the study’s findings, which come amid a five-year trend of increasing marijuana use in the U.S. workforce.

“We have to slow down this reckless experiment of pot legalization.”

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“This data is indeed troubling, but it is not surprising,” said the group’s founder and president, Dr. Kevin Sabet.

He continued: “This data mirrors the results we saw when Colorado and Washington legalized marijuana and are numbers we can expect to see any time a state foolishly follows their example. Do we want our pilots, doctors, and truck drivers stoned? We have to slow down this reckless experiment of pot legalization.”

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The states that have legalized marijuana for recreational use include Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon, Vermont and Washington, plus Washington, D.C.

Thirteen additional states have decriminalized marijuana usage but have not made it fully legal.

Kyle Becker is a content writer and producer with LifeZette. Follow him on Twitter