Prince died from an overdose of fentanyl, 'the Ebola of opioids.' What is it?

The Midwest Medical Examiner's Office released its report into Prince's death Thursday afternoon. The superstar, according to the report, died of "fentanyl toxicity": There was more of the drug in his system than his body could handle.

The report said the drug was self-administered. The death was ruled an accident. No further details have been released.

What is fentanyl?

Fentanyl is an opioid painkiller that's typically used in treating severe pain associated with end-stage cancer patients. It is also used as an anesthetic, often for endoscopic or oral surgeries or to relieve pain for women in labor.

The Centers for Disease Control and Prevention considers it to be between 50 and 100 times more potent than morphine.

The drug, according to the National Institutes of Health, works, like other opioids, "by binding to the body's opiate receptors, highly concentrated in areas of the brain that control pain and emotions. When opiate drugs bind to these receptors, they can drive up dopamine levels in the brain's reward areas, producing a state of euphoria and relaxation."

Is fentanyl a pill?

Fentanyl is a synthetic opioid. It's available in several forms: intravenously for patients in surgery, as a lozenge or in a patch that's applied to the skin, allowing it to absorb over a longer period of time.

The U.S. Food and Drug Administration has released a number of warnings about the dangers of fentanyl patches. The CDC released guidelines in March that caution doctors about prescribing opioids like fentanyl to treat chronic pain, saying non-opioid methods are preferred.

How can fentanyl kill? Is overdose common?

Dr. Charles Reznikoff, an addiction medicine specialist at Hennepin County Medical Center, said fentanyl is among the most dangerous of opioid painkillers.

"Fentanyl is what I call the Ebola of opioids. The reason I call it that is fentanyl kills you quickly, very quickly," Reznikoff said.

"Many of the other opioids take a long time and are less apt to kill you in overdose, but fentanyl is so potent, that any little error with the use of fentanyl leads to death."

The CDC issued a warning in October 2015 about increased fentanyl-related fatalities.

And the Drug Enforcement Administration reported that more than 700 deaths related mostly to illegal fentanyl use were reported between the end of 2013 and the beginning of 2015. Agency officials warned that number may be low because many coroners and crime labs don't test specifically for fentanyl.

While fentanyl is typically produced by pharmaceutical companies, it can also be made in illegal operations and distributed as a street drug. Law enforcement officials in the region traced a spate of recent fentanyl overdoses to an illegal lab in Mexico. Fentanyl can be combined with cocaine or heroin to increase the potency of the illegal drugs.

According to the NIH, "the type of fentanyl associated with recent overdoses was produced in clandestine laboratories and mixed with (or substituted for) heroin in a powder form."

Even with Thursday's announcement, there are few details — and many questions — in the story of Prince's death. Autopsy results don't indicate whether the fentanyl that killed the musician was prescribed to him by a doctor. The Carver County Sheriff's Office said its investigation into Prince's death is ongoing.