The percentage of positive drug tests among American workers has increased for the first time in more than a decade, fueled by a rise in marijuana and amphetamines, according to an analysis of 8.5 million urine, oral fluid and hair workplace drug test results by Quest Diagnostics.
The positivity rate for 7.6 million urine drug tests in the combined U.S. workforce increased to 3.7 percent in 2013, compared to 3.5 percent in 2012. The relative increase of 5.7 percent year-over-year is the first time the positivity rate for combined national workplace urine drug tests has increased since 2003.