Sasha Czack, Sylvester Stallone's first wife, told the New York Post that her son was taking painkillers after having five teeth removed two weeks before he was found dead.
"I told him not to do that. I've heard about people dying having multiple procedures done to your mouth. Do not have more than one tooth [pulled]," she said.
An autopsy was completed on Sage's body on July 16 but the results were deferred. His funeral will be held on Saturday (July 21).
Sylvester Stallone released a statement on Monday (July 16) calling for an end to "speculation and questionable reporting" about his son's death.
"When a parent loses a child there is no greater pain," he said. "Therefore, I am imploring people to respect my talented son's memory and feel compassion for his loving mother, Sasha.
"This agonizing loss will be felt for the rest of our lives. Sage was our first child and the centre of our universe, and I am humbly begging for all to have my son's memory and soul left in peace."