Matthew Perry died due to the "acute effects of ketamine".
The 'Friends' star passed away in October, aged 54, and his cause of death has now been revealed, after he was found dead at his home in Los Angeles.
The autopsy report - which has been obtained by PEOPLE - also lists drowning, coronary artery disease and buprenorphine effects as contributing factors in the actor's death.
Perry was on ketamine infusion therapy, according to the autopsy, which reports that his last treatment took place just "one and a half weeks before" his death.
Perry - who was found dead in a "residential pool" - suffered from drug and alcohol addiction, and buprenorphine is a medication that's used to treat opioid use disorder.
The actor's death is considered to be accidental. The report states that no foul play is suspected.
Meanwhile, Perry's 'Friends' co-stars - Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matt LeBlanc and David Schwimmer - issued a joint statement shortly after the actor passed away, admitting that they were "devastated" by the news.
They said at the time: "We are all so utterly devastated by the loss of Matthew.
"We were more than just castmates. We are a family. There is so much to say, but right now we're going to take a moment to grieve and process this unfathomable loss. In time we will say more, as and when we are able.
"For now, our thoughts and our love are with Matty's family, his friends, and everyone who loved him around the world."
Perry - who played the part of Chandler Bing on 'Friends' - was laid to rest at the Forest Lawn cemetery in Los Angeles in November.