The drug that killed Prince is a narcotic so powerful that it was blamed for the accidental deaths of as many as 120 hostages when Russian forces used it to subdue Chechen terrorists during the 2002 siege of a packed Moscow theater.
A medical examiner's report Thursday said Prince — who was found dead April 21 in an elevator at his home studio in Chanhassen, Minnesota — died from fentanyl toxicity.
The autopsy report from the Midwest Medical Examiner's Office in Ramsey, Minnesota, gave no details apart from declaring that Prince, 57, died from an apparently self-administered dose of fentanyl. It's still not known how he got the drug or, if it was prescribed, why.
But at the time of his death, Prince was being treated for opioid withdrawal, as well as anemia and a fatigue, a source with knowledge of his treatment told NBC News.
Meanwhile, local investigators have asked for help from the U.S. Drug Enforcement Administration, federal law enforcement officials have told NBC News.
"This was a man in his 50s who may have been struggling with pain and took a very potent opioid analgesic and died accidentally from an overdose," Barbarajean Magnani, pathologist-in-chief at Tufts University Medical Center of Boston, told NBC station KARE of Minneapolis on Thursday.
"Celebrities bring it to our attention, but we see this every day," Magnani said. "We have to re-examine the way we're treating pain."
Fentanyl is a synthetic opioid — its chemical name is the tongue-twisting N-phenyl-N-[1-(2 phenylethyl)-4-piperidinyl] monohydrochloride — that was first formulated during the 1950s as a safer and more effective alternative to the painkillers morphine and meperidine.
Its creators at the Belgian drug company Janssen Pharmaceutica got the "more effective" part right.
Fentanyl is the strongest opioid approved for medical use in the United States, rated as 50 to 100 times more potent than morphine and 30 to 50 times more potent than heroin, according to the National Institute for Drug Abuse.
It's the go-to drug to dull the crippling, otherwise-untouchable pain experienced by many patients with advanced cancer.
The safety part of the equation is another matter.
According to research published in the journal Annals of Pharmacotherapy, as little as a quarter-milligram of fentanyl can be fatal. To appreciate how tiny an amount that is, consider that a standard aspirin tablet is 325 milligrams — 1,300 times bigger.
Its effects are also almost immediate, depending on how it's used — especially if it's inhaled. That's what happened Oct. 26, 2002, at the Dubrovka Theater in Moscow, where Chechen rebels had taken more than 850 people hostage three days earlier.
Russian special forces raided the theater on the 26th, bombarding it with a sedative gas to incapacitate everyone inside. When the siege was over and the bodies had been counted, the dead included about 120 of the hostages.
The Russian Health Ministry later disclosed that the gas was trimethyl phentanylum — a form of fentanyl. Nearly all of the hostages died from effects of the gas or poor treatment afterward, Russian officials acknowledged.
Later analysis of victims' clothing by the National Center for Biotechnology Information, an agency of the U.S. National Institutes of Health, found that the aerosol also included carfentanil and remifentanil — two more forms of fentanyl.
With a narcotic so powerful, abuse and illegal trafficking are bound to follow, and government statistics show that fentanyl has become one of the deadliest pharmaceuticals the Drug Enforcement Administration has to deal with.
Fentanyl-related overdoses killed more than 700 people nationwide from late 2013 to early 2015, the most recent report period for which complete data are available, according to the DEA. That's confirmed deaths reported to only one agency.
Over a similar period from 2005 to 2007, the DEA and the Centers for Disease Control and Prevention reported 1,103 fentanyl-related deaths — from non-medical uses alone (PDF).
And the actual number of deaths attributable to fentanyl is likely much higher, according to the DEA, which notes that in many jurisdictions, medical examiners don't even test for it unless they're specifically asked to.
Emergency rooms reported almost 4,600 fentanyl-related seizures in 2014 alone, according to theCDC.
While an not-insignificant number of deaths are the result of accidental misuse or overdose of properly prescribed fentanyl, most come from "abuse for its intense euphoric effects," the agency said (PDF).
"Fentanyl can serve as a direct substitute for heroin in opioid-dependent individuals. However, fentanyl is a very dangerous substitute for heroin because it is much more potent than heroin," it said.
Drug pushers often mix it with heroin or cocaine, which only increases their potency and danger.
More than a year ago, in March 2015, the CDC issued a nationwide alert classifying fentanyl as a significant "threat to public health and safety," especially for public health workers, first responders and law enforcement personnel. That's because it can deliver a fatal dose simply through not only inhalation but also accidental skin contact, the CDC said.
Following a surge of fentanyl-related deaths in the Chicago area in the last six months, Peter Koin, deputy chief toxicologist for the Cook County medical examiner's office, called the drug a "great public health risk," because "people may not know they're using a very powerful drug."
"In addition, we're seeing new versions of fentanyl, and testing for these substances is challenging because we've never seen them before," Koin said. "It's something brand new."
Paul Wax, executive director of the American College of Medical Toxicology, told KARE on Thursday that Prince's death will intensify efforts to educate doctors and patients about the risks of fentanyl and other powerful synthetic opioids.
"The epidemic spares no one," Wax said. "It affects the wealthy, the poor, the prominent and not prominent. That's the nature of an epidemic."