Facts and background about fentanyl

A person close to the investigation of Prince's death told The Associated Press on Sunday that pills found in Prince's home marked as acetaminophen-hydrocodone actually contained fentanyl, suggesting they were counterfeit pills obtained illegally.

Because of the risk of abuse, overdose and addiction, the Food and Drug Administration imposes tight restrictions on fentanyl; it is classified as a Schedule II controlled substance.

More than 700 fentanyl-related overdose deaths were reported to the DEA in late 2013 and 2014.

Since many coroners and state crime labs don't routinely test for fentanyl, the actual number of overdoses is probably much higher.

[...] longtime friend and collaborator Sheila E. has told the AP that Prince had physical issues from performing, citing hip and knee problems that she said came from years of jumping off risers and stage speakers in heels.

Some users — whether they start as recreational users or legitimate pain patients — become addicted, experiencing an inability to control how much they take, so they use much more than is prescribed or seek out drugs on the black market.