Prescription drugs were found in Prince's possession when he died, according to reports in the US.
Officials told NBC News the painkillers were discovered in his Minneapolis home - but is it unclear if they played any part in his death.
The singer died on April 21 after collapsing in a lift at his Paisley Park compound.
A coroner has said it could be weeks before the results of a post-mortem can be disclosed.
TMZ reported the star was treated for an overdose of the painkiller Percocet less than a week before he died.
It is claimed his plane had to make an emergency landing in Illinois as he returned from performing in Atlanta.
But the Purple Rain singer reportedly refused to stay in hospital as they did not have a private room for him.
However, airport and public safety officials have refused to confirm such reports.
Long-time friend and collaborator Sheila E said Prince had physical issues from years of jumping off stage speakers in heels.
His lawyer L. Londell McMillan said the singer may have taken pills to manage pain but refuted claims he had a drug problem.