The Province of British Colombia said via their website:
The BC Coroners Service announces the cause of death of Cory Monteith was a mixture of toxicity, including heroin and alcohol. Mr. Monteith, aged 31, was found deceased in his room at the Fairmont Pacific Rim hotel in downtown Vancouver, British Columbia, shortly after noon on July 13.
The investigation into this death by the BC Coroners Service is continuing, and no other details are available at this time. It should be noted that at this point there is no evidence to suggest Mr. Monteith’s death was anything other than a most-tragic accident. When the investigation is concluded, a Coroners Report will be issued.
Mr. Monteith’s family has been made aware of the circumstances surrounding the death. On behalf of family members, the BC Coroners Service asks that the media respect their privacy at this difficult time.
The BC Coroners Service expresses its sincere condolences to Mr. Monteith’s family and friends.
Monteith’s autopsy was conducted on July 15, along with a toxicology test, the results were not expected to be released for some time.
Playing with candid naiveté a jock-turned-geek on screen, Monteith amassed a great deal of fandom and rapidly shot to fame. Reeling from the news of his untimely death, his loving fans and grieving co-stars have expressed their shock and dismay.
Monteith had battled substance abuse problems throughout his life. In April, it had been announced that he would sit out the final two Glee episodes of the season to attend rehab.
#BreakingNews: BC coroner's office confirms #CoryMonteith died of an overdose involving heroin and alcohol
— ABC Entertainment (@ABCNewsEnt) July 16, 2013