Sage, the oldest child of actor Sylvester Stallone, was found dead at his Hollywood home on Friday, July 13 by an unnamed relative and an employee.
The coroner's office has now confirmed that Sage, who was 36 years old at the time of his passing, died from a condition that causes a blockage of the arteries.
According to The AP, the level of the pain medication hydrocodone in his system was found to be minimal upon investigation.
No other factors were involved in Sage's death, and foul play was not suspected.
Sage made his acting debut opposite his father in Rocky V, playing the role of Rocky's son Robert Balboa. He appeared with his dad again in Daylight, and went on to direct, produce and write.
Sylvester Stallone recently said that his "good friends" and the support of his family had been of great comfort in the immediate aftermath of his son's death.