Four percent of U.S. worker drug tests were positive last year, up slightly from the previous year, the medical screening laboratory Quest Diagnostics reports.

Increases were found in both the general workforce and the “safety-sensitive” workforce, which includes pilots, truck drivers, subway engineers and other transportation workers, according to The Wall Street Journal. Positive drug test results rose for the third year in a row, after decades of declines, the article notes.

Almost half of workplace positive drug tests were for marijuana. Detection of the two most common prescription opioid painkillers, hydrocodone and hydromorphone, fell in 2015.

The findings are based on more than 9.5 million urine tests.