The rate of positive workforce drug tests is the highest it has been since 2004, according to an analysis by the drug testing lab Quest Diagnostics. More than 2 percent of U.S. employees tested positive for drugs last year, The Wall Street Journal reports.

The number of employees and job applicants who tested positive for marijuana increased 10 percent last year, to 2.3 percent. The tests indicate marijuana use increased for workers including those in safety-sensitive positions such as nuclear power-plant operators, airplane pilots and train conductors.

The number of drug tests indicating signs of heroin, cocaine and prescription opioids declined from 2017 to 2018.

“Our in-depth analysis shows that marijuana is not only present in our workforce, but use continues to increase,” Barry Sample, PhD, Quest Diagnostic’s senior director of science and technology said in a news release. “As marijuana policy changes, and employers consider strategies to protect their employees, customers and general public, employers should weigh the risks that drug use, including marijuana, poses to their business.”