Drug use has continued to rise among U.S. workers, but rates in Texas — though slightly higher than the national average — are dropping for some drugs, an analysis finds.

Nationally, the rise is attributed to an increase in use of cocaine, methamphetamine and marijuana, according to data from Quest Diagnostics, one of the nation’s largest lab testing companies.

"Four or five years ago, things were plateauing for a number of drugs and from an overall test positivity perspective," said Barry Sample, senior director of science and technology at Quest.

But the rate of positive tests for illicit drugs is once again on the rise. "And that should be of concern for employers ... and everyone concerned about a safe and productive workplace," he said.

Quest has released an annual drug testing index since 1988. The latest interactive map, which looks at how often members of the workforce test positive for "potentially dangerous" forms of prescription and illicit drug use, is based on data from 10 million drug test results.

Although the data provides interesting insight into how often employees test positive for certain drugs, the raw numbers can still be difficult for businesses to meaningfully use, said Marianne Fazen, executive director of the Dallas-Fort Worth Business Group on Health.

Texas saw a reduction in cocaine use over the past decade, with 0.68 percent of workers testing positive in 2007 compared to 0.44 percent in 2017. But rates of positive lab test results for opiates, amphetamines and marijuana went up.

The percentage of Texas workers testing positive for an opiate more than doubled from 0.21 percent in 2007 to 0.55 percent in 2017. Marijuana jumped from 1.8 percent to 2.4 percent. The percentage that tested positive for amphetamines rose from 0.51 percent of tested workers 10 years ago to 1.1 percent last year.

One challenge is that drugs like opioids and marijuana can be prescribed, Fazen noted. The Quest data does not differentiate between an employee using them legitimately versus illicit use.

"It makes business sense for companies to invest in drug testing. But, what do you do with the results when you get them?" Fazen asked.

"Companies open the Pandora's box and need to be ready for dealing with the results. We need to slice the data a little more deeply to try to figure out what the challenges really are. We have our work cut out for us."

Overall, about 4.7 percent of Texas workers who underwent drug testing at a Quest lab in 2017 tested positive for the tracked drugs, which also include heroin and the hallucinogen phencyclidine. Still, the Texas rates are down overall from 2014, when 5 percent of workers' labs tested positive.

The overall national rate remained at 4.2 percent last year, maintaining the highest rate recorded since 2007.

The test results Quest examines include workers in industries that perform public safety and national security jobs, like pilots, bus drivers, law enforcement and power plant workers. Those employees are subject to mandatory drug testing by federal regulators.

Sample agrees that a deeper dive into legitimate versus illicit use could prove helpful. But he says that just knowing the raw numbers can also help employers keep a finger on the pulse of what is potentially happening within the workforce.

"Just because an individual has a prescription for the drug that the laboratory identified doesn't necessarily mean that they are using it as prescribed," he said. "And even if they're using it as prescribed, that doesn't mean it doesn't have an impact on the safe performance of their duties."