Carfentanil is an opiate 10,000 times more powerful than morphine. And since last summer, it’s been killing addicts and confounding first responders across the country.

The drug was never intended to be consumed by humans. But it has been used to kill and immobilize humans — reportedly, in assassination attempts and by Russian Special Forces in 2002. They apparently used it in aerosol form as a knockout gas to end a hostage situation. Tragically, the gas ended up killing more than 100 hostages.

“Carfentanil is a synthetic opioid. It’s of a drug class similar to fentanyl and other fentanyl analogs,” Terry Boos says.

Boos is the section chief for the Diversion Control Division, of the DEA’s Drug and Chemical Evaluation section. He says the only legitimate use of the drug is as a tranquilizer for very large animals, like elephants or hippos. So there’s no medical literature to consult for its effects on humans. That knowledge is being gained the hard way, by first responders.

“During the month of July [2016], paramedics in Akron registered more than 230 drug overdoses, with 14 of those being fatal,” DEA spokesman Russ Baer says.

“Those were eventually linked to carfentanil. Thereafter we saw outbreaks throughout Ohio, particularly in Cincinnati.”