A federal agent gave rapper Juice Wrld an opioid antidote on a plane before he died, police have said.
The aircraft carrying the 21-year-old rapper and about a dozen other people landed at Midway International Airport at around 2am on Sunday.
Authorities were searching the plane after receiving a tip-off that drug and guns were on board.
During the search, the 21-year-old rapper started to have a seizure, Chicago police spokesman Anthony Guglielmi said.
One agent administered Narcan after the rapper's girlfriend said Juice, whose real name was Jarad Higgins, had been taking opioid painkiller Percocet.
Higgins woke up but remained incoherent, the Chicago Tribune reported. He was rushed to Advocate Christ Medical Centre in Oak Lawn, where he was pronounced dead.
An autopsy was completed on Monday but the toxicology test results are still pending, the medical examiner's office said. However, foul play is not suspected.
During the plane search, a sniffer dog made a "positive alert" on luggage carts that were loaded with bags from the plane, Mr Guglielmi said.
Inside, they found multiple bags of suspected marijuana, several bottles of prescription cough syrup, three guns, metal-piercing bullets and a high-capacity ammunition magazine.
None of the dozen or so people on the plane admitted to carrying the drugs, but detectives are conducting a forensic analysis to determine which bags belonged to which passengers.
He added that two security guards who were on the plane were arrested on misdemeanour gun charges.
