An autopsy and toxicological analysis, performed Monday, said “mixed drug toxicity, involving heroin and alcohol” killed the 31 year-old actor.
Monteith was found at Vancouver’s Fairmont Pacific Rim hotel on Saturday.
The investigation into his death is still ongoing but Canadian authorities call the incident a “most tragic accident.”
“Mr. Monteith’s family has been made aware of the circumstances surrounding the death,” the BC Coroners Service said in a statement. “On behalf of family members, the BC Coroners Service asks that the media respect their privacy at this difficult time.”
Monteith checked into the Fairmont Pacific Rim hotel on July 6 and had been expected to check out on July 13 but never left his room. Hotel staff found the actor’s lifeless body shortly after noon on Saturday.
Monteith, born in Victoria, British Columbia, had a history of substance abuse, telling Parade magazine in 2011 that he began using drugs at 13 and by 19 was in rehab for using “anything and everything, as much as possible.”
“I’m lucky on so many counts,” the actor said. “I’m lucky to be alive.”
Monteith was scheduled to return to “Glee” for a fifth season this fall.
In a statement released over the weekend, “Glee” executives said they were “deeply saddened by this tragic news. Cory was an exceptional talent and an even more exceptional person.”
Monteith recently wrapped shooting his final acting role, the independent film “McCanick,” in which he plays a drug-addicted street hustler.