A new report from the Drug Enforcement Administration (DEA) finds controlled prescription drugs, including opioids, are responsible for the largest number of overdose deaths of any illicit drug class since 2001.

“Traffickers are now disguising other opioids as controlled prescription drugs to gain access to this market,” the DEA said in a news release.

A total of 63,632 people died from drug poisoning in 2016 in the United States, USA Today reports. More than 40,000 deaths involved prescriptions including opioids. Fentanyl and other synthetic opioids were involved in almost 20,000 deaths last year, the article noted.

The DEA also reported Mexican cartels continue to make large quantities of cheap methamphetamine that makes its way to the United States.