Credit: In this Aug. 9, 2016, file photo, a bag of 4-fluoro isobutyryl fentanyl which was seized in a drug raid is displayed at the Drug Enforcement Administration (DEA) Special Testing and Research Laboratory in Sterling, Va. Acting United States DEA administrator Chuck Rosenberg will visit China next week amid efforts to cut off the Chinese supply of deadly synthetic drugs, like fentanyl. China disputes U.S. claims that it’s the top source of opioids. Still, Beijing has already banned fentanyl, an opioid some 50 times stronger than heroin, and 18 related compounds. (AP Photo/Cliff Owen, File)
Opioid crisis: Stronger street drugs can render Narcan useless
