The percentage of American employees testing positive for a drug test last year has reached its highest rate since 2001, mostly driven by an increase in marijuana usage, as businesses continue to grapple with the ongoing nationwide labor shortages.

The annual drug testing index by Quest Diagnostics Inc., one of the nation's largest drug testing laboratories, found the overall positivity rate in drug tests was up to 4.6 percent in 2021, compared to 4.4 percent in 2020. 

The report was based on nearly 9 million urine drug tests collected between January and December 2021.

"Our Drug Testing Index reveals several notable trends, such as increased drug positivity rates in the safety-sensitive workforce, including those performing public safety and national security jobs, as well as higher rates of positivity in individuals tested after on-the-job accidents," Barry Sample, senior science consultant for Quest Diagnostics, said in the news release.

Positivity rates for marijuana in the U.S. workforce have continued to climb upward, with 3.9 percent of the urine tests coming back positive, an increase of more than 8 percent from 2020. The company noted that positive tests for marijuana in the general U.S. workforce increased 50 percent since 2017.

Sample said the shifting attitude toward marijuana has prompted some employers, including Amazon, to stop testing for the drug, while other companies in some states are barred from factoring the test results into hiring decisions, according to The Wall Street Journal.

“We’ve been seeing year-over-year declines in those recreational-use states, but by far the largest drop we’ve ever seen was in 2021,” he said about the number of drug tests that screened for THC.

Quest’s data showed that the percentage of positive THC tests declined by 6.7 percent nationwide in 2021 from 2020. The number also fell by 10.3 percent in states where recreational marijuana is legal.

“We certainly heard from some of our employer customers that they were having difficulty finding qualified workers to pass the drug test,” Sample said of pre-employment tests for THC, according to the Journal.

The increase in positive tests comes as the House is set to pass legislation this week that would legalize marijuana. Still, 18 states have already legalized the drug for recreational use, including the District of Columbia.