The service said the coroner found no trauma or injury to Monteith's body, nor evidence of foul play. Instead, the report noted investigators found drug paraphernalia, including a spoon with drug residue and a used hypodermic needle, in Monteith's room at the luxury Fairmont Pacific Rim hotel.
Two empty champagne bottles and some glasses were also found on a nearby table.
The alcohol, combined with the heroin, allowed the coroners' service to conclude Monteith's death was an accident, likely in part due to the actor's admitted past of drug abuse peppered with stints in rehab.
Toxicology results indicate the Canadian actor had a "moderate level of intoxication" from alcohol, as well as traces of a metabolite of heroin in his blood, the coroner's report said.
"Alcohol and heroin are both central nervous system and respiratory depressants," it said.
"In combination, these drugs can cause sedation and death. Heroin is classified as an opioid drug; individuals typically build up a concentration tolerance to this type of drug over time. After a period of cessation from opioid drug use, a previously tolerated drug concentration level may become toxic and fatal."
The coroner's final report on Monteith's death is similar to its initial findings.
Monteith, who played football star and singing sensation Finn Hudson in the popular television series "Glee," was found unresponsive "in a collapsed position" on his hotel room floor around noon on July 13, said the coroner's final report.
He had checked into the Fairmont several days earlier, and was expected to check out on the day he died. When he hadn't done so, hotel staff went to check on him in his room, and found him on the floor.
Monteith had spent the previous evening out with a few friends, but video footage from the hotel shows the actor returned alone to his room.
Monteith's death prompted fans to set up a memorial for him outside the hotel, laying down flowers, cards, and stuffed animals, but the shock of his death resonated around the world.
He was recently honoured at the Emmy Awards, along with actors such as James Gandolfini of "The Sopranos" fame, and Jean Stapleton of "All in the Family."