The painkiller is 50 times more potent than heroin.

Amid all the speculation and controversy, the death of legendary artist Prince has been officially ruled an accidental opioid overdose. The Midwest Medical Examiner's Office in Minnesota released an autopsy report yesterday listing the cause of his death as an accident, and citing fentanyl toxicity.

Fentanyl is a synthetic opioid painkiller approved for treating very severe pain. While it's in the same class as more commonly prescribed opioids (such as oxycodone), the Centers for Disease Control and Prevention (CDC) warns that fentanyl is 50 times stronger than heroin and 100 times more potent than morphine. The Drug Enforcement Agency (DEA) describes fentanyl as the "most potent opioid available for use in medical treatment."

In an interview with People, addiction expert Ben Levenson said the drug was originally intended for palliative care—to relieve the suffering of people with grave illnesses. He explained that fentanyl is not ideal for regular pain management: "It hits you fast and it wears off fast, so it's not a good drug for someone who is, for instance, recovering from knee surgery, although it's widely prescribed. It was never designed for that."

Levenson, who founded a series of addiction treatment centers called Origins Behavioral Healthcare, also pointed out that fentanyl is prescribed in micrograms as opposed to milligrams because it's so potent. (According to the DEA, a dose as small as 0.25 mg is potentially lethal.) The drug is "highly sought after by addicts," Levenson said.

Fentanyl and other opioids are becoming an enormous problem in the U.S., as more and more people become dependent on them. “We underestimated the addictive potential of opioid painkillers [at first] and they’ve been overprescribed," Antoine Douaihy, MD, a professor of psychiatry and medicine at the University of Pittsburgh School of Medicine, told Health in a previous interview.

The CDC reports that one in four patients treated with long-term opioid therapy in a primary care setting end up struggling with addiction. Since 1999, deaths from prescription opioids have quadrupled.

The problem is that patients build up a tolerance to these drugs. Opioids work on the reward center of the brain, and the more you take them, the more you need to get the same effect.

“We have a health care system that doesn’t provide good education about how to manage pain,” said Dr. Douaihy. “And the easiest answer [for treating patients’ pain] is to give them a prescription for opioid painkillers without taking into consideration any factors that could put them at risk for misusing or abusing them.”

"If a patient reports, 'My pain is an 8,' you have to treat them at an 8," Levenson told People. "The reason people get to the level of needing fentanyl, and doctors going ahead and prescribing them is because they've worked their way through lower-strength opiates."

Fentanyl is administered in a variety of ways, under various brand names. Duragesic is a skin patch, for example; Sublimaze is an injection; and Acqtic is delivered orally through a "lollipop."

According to the CDC, most fentanyl-related overdoses and deaths are linked to an illicit version of the drug that's often mixed with heroin or cocaine. The situation is getting worse very quickly. In Ohio, for example, the agency estimates that there was a 500% surge in fentanyl-related overdoses between 2013 and 2014. Last March, the DEA issued a national alert classifying fentanyl as a threat to health and public safety. And the New York Times recently reported that in some states, accidental deaths due to fentanyl abuse are surpassing the number of deaths from heroin abuse.

If you have been prescribed fentanyl or another opioid medication, consult with your doctor to get all the information you need to take the drug safely, including the correct dosage and frequency, and whether any underlying health issues put you at higher risk for an overdose.