Drug use by the U.S. workforce remains at its highest rate in more than a decade, driven by increases in cocaine, methamphetamine and marijuana, according to a new study.

The findings come from the drug-testing laboratory Quest Diagnostics, which analyzed more than 10 million urine tests conducted on behalf of employers. The company found positive tests for prescription opioids dropped 17 percent in 2017 from the previous year, The Wall Street Journal reports. This drop likely reflects the continuing crackdown on illegal or excessive opioid prescriptions, according to Barry Sample, Ph.D., Senior Director of Science and Technology at Quest Diagnostics.

Quest found the share of U.S. workers and job applicants who tested positive for illicit drugs in 2017 was 4.2 percent, the same as the prior year.