A combination of opiate plus a street drug has hit the market. The researchers say that the quasi-legal drug combo is 15 times stronger than heroin.

Researchers at the University of North Carolina at Charlotte, N.C. have advised emergency room doctors to be on the lookout for this drug as there could be "an upswing in what on the surface appear to be heroin overdoses". The drug combination masquerades as heroin, confusing both the users and the doctors who treat overdoses.

The team sais that Acetyl fentanyl is often mixed with other street drugs and sold as heroin. Recently, the North Carolina Department of Health and Human Services issued an advisory saying that Acetyl fentanyl is linked to three overdose deaths.

Acetyl fentanyl isn't an approved pain medication, but it resembles prescription pain killing opioid, fentanyl.

"What's frightening about this emerging street drug is that users themselves may not be aware that they are ingesting it," said John Stogner, Ph.D. of the Department of Criminal Justice and Criminology at the University of North Carolina at Charlotte, N.C.

"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. Larger or additional doses are necessary when acetyl fentanyl is responsible. It's never good to lose time between overdose and treatment," Stogner, lead author of the study, said in a news release.

Acetyl fentanyl is classified as opiate analgesic, but has no medical use. The drug is about five times stronger than heroin and most users are unaware that high doses of the drug can lead to severe complications. The drug is in a legal grey area as it is considered illicit for human consumption, but is no exactly legal.

The study is published in the journal Annals of Emergency Medicine.