Mexican Lab Closed Down After Suspicions that Painkiller Killed Heroin Users in U.S.

U.S. agents, working in cooperation with the Mexican government, have closed down a lab in Mexico that might be the main source of a powerful painkiller that has killed at least 100 heroin users in eight states, the federal drug czar said Monday.

John Walters, director of the White House Office of National Drug Control Policy, said it's still not clear whether the painkiller,fentanyl, was mixed with heroin at the lab in Mexico or after it entered the United States.

"There may be more than one source," Walters said. "We think this is the principal source."

Five people were arrested during the May bust, including one Walters described as "the chemist." He referred specific questions to the U.S. Drug Enforcement Agency, which declined to provide details immediately.

Walters said that the dealers may have started using Fentanyl because they were looking for a competitive advantage on the street, but that inept mixing — or cutting — of the drug combination made it deadly.

He also warned that millions of deadly doses of the fentanyl-laced heroin might still be on the streets. Fentanyl-laced cocaine had turned up in some cities, as well, he said.

Deaths caused by fentanyl-laced drugs have occurred in Illinois, Michigan, Missouri, Ohio, Pennsylvania, New Jersey, Delaware and Maryland, Walters said.