A close cousin to its namesake, acetyl fentanyl has been sold on the streets in packages marked as heroin.

A new and powerful drug that is 15 times stronger than heroin has made its way onto streets and resulted in a wave of emergency room visits across the country.

Acetyl fentanyl is a relative of the painkiller fentanyl, but it’s being mixed into street drugs that are marketed as heroin. It’s not recognized as having any medicinal benefits in the U.S. and is not regulated in any way, which has led to users being able to easily obtain it. It’s classified as not being fit for human consumption, but has managed to remain legal by the package being labeled as “not for human consumption.”

The opiate is typically used intravenously and taken as a substitute for heroin. However, many users are unaware that what they are injecting isn’t actually heroin.

“A patient may report heroin use and have symptoms consistent with heroin overdose, but an emergency physician may find that the standard dose of antidote—naloxone—doesn’t work,” said scientist John Stogner, from the Department of Criminal Justice and Criminology at the University of North Carolina. “Larger or additional doses are necessary when acetyl fentanyl is responsible. It’s never good to lose time between overdose and treatment.”

Numerous people throughout the Northeast have died over the last year from overdosing on fentanyl-laced heroin, which is 100 times more powerful than morphine and typically only given in extreme cases like end-of-stage cancer patients. Dealers have been marketing the drug across the country with names like “Bud Light” and “Income Tax.”

The Drug Enforcement Administration warned local authorities last January about the “killer heroin,” but also urged them to exercise caution when handling it because fentanyl can be absorbed through the skin.