A growing number of people in the United States are using methamphetamine and fentanyl, often together, according to a new analysis of urine drug tests.

Between 2013 and 2019, urine samples that tested positive for meth rose sixfold—from 1.4% of samples in 2013 to 8.4% in 2019, HealthDay reports. The percentage of samples testing positive for fentanyl more than quadrupled during that period. Just over 1% of urine samples tested positive for fentanyl in 2013, compared with almost 5% in 2019.

The rate at which urine samples testing positive for fentanyl also tested positive for meth increased almost 14-fold, the researchers reported in JAMA Network Open. The rate at which fentanyl-positive urine samples also tested positive for cocaine and heroin rose by more than sixfold.