Fentanyl, the powerful drug that killed Prince, was developed as morphine alternative

When Prince was found dead of an accidental overdose in April, the drug fentanyl, a synthetic opiate up to 100 times stronger than morphine, was lingering in his veins, a medical examiner's report said Thursday.

The beloved musician was the most famous casualty of this potent drug, which the Centers for Disease Control and Prevention says is responsible for hundreds of overdose deaths per year in the past few years.

First developed in a lab in the 1960s, fentanyl was intended to be an alternative to morphine. It's used by doctors to ease the wrenching pain of some cancer treatments or for people undergoing surgery, particularly those who don't respond to other narcotics. It is fast-acting, crossing the blood-brain barrier more quickly than other drugs, and ruthlessly efficient in targeting the body's opioid receptors.

The drug is so powerful that prescriptions are written out in microgram doses; a tablet the size of an average aspirin pill would easily kill you. Overdoses can be reversed with naloxone, a fast-acting antidote, according to the CDC - but such overdoses may require higher or multiple doses of the medication to counteract fentanyl's potency.

It's not clear whether Prince had a prescription for fentanyl. According to court records, the physician who found Prince on the day of his death had been treating him for several weeks. That week, the musician was also scheduled to meet with a Northern California doctor who specializes in opioid addiction.

Fentanyl is extraordinarily easy to misuse, even unintentionally. The drug's potency and efficacy makes it ripe for abuse, and the fact that it is usually prescribed as a patch or lozenge rather than an injection makes overuse even easier, according to Caleb Alexander, co-director of the Johns Hopkins Center for Drug Safety and Effectiveness. Illicit use is also a growing problem, the U.S. Drug Enforcement Administration says: It is increasingly winding up in the wrong hands through pharmacy theft, fake prescriptions and illegal distribution by doctors and patients.

Just as problematic is illegally-made, non-pharmaceutical-grade fentanyl, which officials believe is driving a growing number of overdose deaths. According to the CDC, fentanyl seizures by law enforcement jumped 700 percent between 2012 and 2014. During the end of that upswing - from the last months of 2013 through 2014 - 700 people died in a fentanyl-related incident. Actual fatality numbers are likely even higher, since coroners and crime labs don't always know to test for the drug.

One person interviewed in a March study of 12 Australian fentantyl users said, "Once people go to fentanyl, they make that change, they can't go back because they just want stronger, stronger, stronger, and so fentanyl is the strongest."

"They can't go back, you know," the participant concluded. "[Other opiates] are s---."

Reading aloud Prince's one page autopsy report Thursday, Barbarajean Magnani, pathologist-in-chief at Tufts Medical Center, noted that Prince's death - and fentanyl misuse generally - are part and parcel of an ongoing opioid epidemic whose casualties are now in the tens of thousands.

"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," he said, according to The Associated Press. "Celebrities bring it to our attention, but we see this every day. We have to re-examine the way we're treating pain."

READ: Prince death ruled a painkiller overdose

The CDC has urged doctors to limit opioid prescriptions, citing the spiking number of overdoses.

"What we want to just make sure is that doctors understand that starting a patient on an opiate is a momentous decision," director Tom Frieden said in December. "The risks are addiction and death, and the benefits are unproven."

In 2014, more than 18,000 Americans died from prescription opiod overdoses, according to the Department of Health and Human Services - a statistic that swamps the 700 deaths from fentanyl. But according to Alexander, fentanyl is disproportionately responsible for injuries and deaths, given how rarely it is prescribed.

Even more so than other opiods, "it is the kind of thing that should be used with extreme caution," he said. "It is so commonly fatal."

Never was that more obvious than during the Moscow theater hostage crisis in 2002. Russian troops pumped sedative gas laced with fentanyl into the Dubrovka Theater, where dozens of armed Chechen rebels had taken more than 800 people hostage. Hundreds of Russian hostages were poisoned by the gas along with the militants, according to the BBC, and some 130 civilians died as a result.

But fentanyl is just as insidiously lethal in small towns and cities in the United States. In 2014, 22 people in Pittsburgh and western Pennsylvania died from overdoses in a single week. The following year, the small Ohio city of Marion saw two dozen people killed in a rash of overdose deaths - accounting for one in every five deaths in the city that year, according to the Marion Star.

Both cases were traced back to fentanyl-laced batches of heroin.

"Add fentanyl to heroin, its potency goes through the roof," DEA acting deputy administrator Jack Riley told The Washington Post in 2015. "Now, all of a sudden they have something people are dying for on the street."

The DEA has tied fentanyl seizures back to Mexican drug trafficking groups, according to the AP. In addition to being used as a heroin additive, the drug may be sold on the street as a powder or formed into counterfeit oxycontin pills. Often, users don't know what they are taking, making the threat of an overdose even more likely.

In the fall, the CDC issued an emergency health advisory addressing the explosion of fentanyl seizures and related deaths. The hardest-hit areas were scattered across the eastern seaboard, but almost no state was spared entirely. In the advisory, the agency also noted that the drug wasn't just dangerous to users: New Jersey law enforcement officers conducting field test reported dizziness and breathing problems after coming in contact with an unknown substance. Lab analysis later showed that it contained fentanyl.

"The epidemic spares no one," Dr. Paul Wax, executive director of the American College of Medical Toxicology told the AP. "It affects the wealthy, the poor, the prominent and not prominent. That's the nature of an epidemic."