MINNEAPOLIS — Some of the pills taken from Prince’s estate in Paisley Park after his death were counterfeit drugs that actually contained fentanyl – a synthetic opioid 50 times more powerful than heroin, an official close to the investigation said Sunday.

The official said nearly two dozen pills found in one Aleve bottle were falsely labeled as “Watson 385.” According to Drugs.com, that stamp is used to identify pills containing a mix of acetaminophen and hydrocodone, but the official said at least one of the pills tested positive for fentanyl.

Autopsy results released in June show Prince died April 21 of an accidental fentanyl overdose. The official said records show the 57-year-old Prince had no prescription for any controlled substances in the state of Minnesota in the 12 months before he died.

Fentanyl has been responsible for a surge in overdose deaths in some parts of the country. When made into counterfeit pills, users don’t always know they’re taking fentanyl, increasing the risk of a fatal overdose.

The Star Tribune first reported about the mislabeled pills in a story published on its website late Saturday.

Some of the dozens of pills seized from Paisley Park were found to have other drugs in them, some were oxycodone or codeine, and some were not controlled substances.

About a dozen tablets were found in a dressing room at Paisley Park, but the vast majority was in bottles of aspirin and vitamin C that had been tucked inside a suitcase and bags.