Fentanyl, a powerful painkiller that a medical examiner identified as the drug that killed the superstar Prince six weeks ago, has been responsible for an epidemic of overdose deaths around the United States, according to federal officials.

The most potent narcotic known, it is a man-made opioid 50 times stronger than heroin and 100 times more so than morphine, according to the U.S. Centers for Disease Control website. The agency says illegally manufactured non-pharmaceutical fentanyl, and related overdoses, are a rising problem.

Fifty-seven-year-old Prince, one of the most influential musicians of his generation, was found dead in his home in a Minneapolis suburb on April 21. He died of an accidental, self-administered overdose of the drug, the county medical examiner said in a death report Thursday.