A new study finds an estimated 1.6 million American adults ages 18 and older reported past-year methamphetamine use between 2015 and 2018.

The study, by the Centers for Disease Control and Prevention, found 52.9% of those who reported past-year meth use had a methamphetamine use disorder, and 22.4% reported injecting meth within the past year. The researchers found co-occurring substance use and mental illness were common among those who used meth within the past year.

“Illegal drugs are cheaper, more potent and more easily available than ever,” Linda Richter, Director of Prevention Research and Analysis at the Center on Addiction in New York City, told HealthDay. “People use methamphetamines because they crave their effects, to enhance or counter the effects of other drugs like opioids, and because prevention efforts are scarce and treatment is expensive, stigmatized and simply in short supply.”