"It's got other opioid effects. Some of these things are 100 or 1,000 times more potent than heroin," said Dr. Michael Miller of Rogers Memorial Hospital in Oconomowoc.
The drug is new to Wisconsin, but law enforcement has found it in Florida and Georgia. Last week, a Pennsylvania man, Jeremy Achey, 43, was sentenced to life in prison for supplying tetrahydrofuran fentanyl.
According to federal court records, a man overdosed and his fiancee died when they bought it from him over the internet. Prosecutors say the seller told customers, "It is best if you snort it, shoot it, or smoke it."
Miller said most addicts do not even know they are taking this synthetic fentanyl.
"Most people who are exposed to synthetic fentanyls are not using them intentionally. They are not desiring to use them because they understand that the potency is so high it could be lethal," said Miller.
Achey is believed to have mailed thousands of packages containing the drug to customers throughout the U.S. In order to survive it, Miller warns you would need a large dose of Narcan.
"Its the fentanyl part that is really fatal because it shuts down your breathing and you die instantly," said Miller. "You use as much opioid reversal agent as you possibly can, you support them, you put them on a ventilator."
The Milwaukee County Medical Examiner's office could not say where the person who died in Milwaukee got the tetrahydrofuran fentanyl. But they warn if one person has it likely others do as well.