Historic decline in U.S. overdose deaths threatened by changing street drug supply

A forensic chemist with the Drug Enforcement Administration holds vials of fentanyl pills at a DEA research laboratory in this file photo. Fentanyl deaths are plunging in the U.S, but the recovery is threatened by a new "synthetic soup" of toxic street drugs.

Drug overdose deaths are plummeting in the U.S. in ways never seen before. Experts worry new, toxic "synthetic" street drugs could derail the recovery.

(Image credit: Mark Schiefelbein/AP)