Medical examiners have found that Prince died from an accidental overdose of the painkiller fentanyl.
The Midwest Medical Examiner’s Office’s report comes more than a month after Prince was found slumped in a lift at his home.
Detectives have already questioned a doctor who saw Prince twice in the weeks before he died.
Prescription painkillers were Prince’s possession following his death at the age of 57, officials told media last month.
A police warrant has also revealed that Dr. Michael Schulenberg prescribed medication to Prince on April 20 – the day before he died.
The warrant does not say what was prescribed or whether Prince took the drugs.
According to the autopsy report, Prince self-administered fentanyl, an opioid many times more powerful than heroin.
In March 2015, the US Drug and Enforcement Administration warned the drug, which it said was often laced in heroin, was a “threat to health and public safety”.
The agency said even small doses of fentanyl could be lethal and that “incidents” and overdoses related to the drug were “occurring at an alarming rate”.
Prince was found unresponsive in a lift at his Paisley Park Studios on the morning of April 21, local officials said. First responders tried to revive him with CPR but he was pronounced dead shortly afterwards.
The singer is believed to have suffered from knee and hip pain from years of performing, the Associated Press news agency reports, citing a friend.
Artists from around the world and Prince’s numerous fans later paid tributes to the star.
Prince was cremated in a private ceremony on April 24. His family is understood to be planning to stage a public memorial in August.