An autopsy report on Matthew Perry listed his cause of death as 'an accident' with the result partly due to the 'acute effects of ketamine'.
The report from the Los Angeles Medical Examiner's office also gives 'drowning, coronary artery disease and the effects of buprenorphine' as contributing factors.
Perry, an advocate for the dangers of alcoholism and a star of the sitcom Friends, died on 28 October resulting in a huge outpouring of affection for him.
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A statement read: "The County of Los Angeles Department of Medical Examiner (DME) determined the cause of death for 54-year-old actor Matthew Langford Perry as the acute effects of ketamine.
"Contributing factors in Mr. Perry’s death include drowning, coronary artery disease and the effects of buprenorphine (used to treat opioid use disorder).
"The manner of death is accident.
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"On October 28, at approximately 1600 hours, Mr. Perry was found unresponsive in the pool at his residence. After 911 was called, paramedics responded to the scene and death was pronounced.
"DME responded, conducted a scene investigation and then transported Mr. Perry’s body to the DME’s Forensic Science Center for examination.
"On October 29, the deputy medical examiner completed an autopsy on Mr. Perry. Following the completion and receipt of relevant test results, the cause and manner of death were certified."
At the time of his death, Perry had been receiving ketamine infusion therapy for depression, and had previously written about it in his book Friends, Lovers and the Big Terrible Thing.
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Ketamine is a general anaesthetic and makes people who use it feel dream-like, relaxed and happy, though it can also produce feelings of confusion and nausea.
It can be used as an anaesthetic for humans and animals, and according to the report Perry's last ketamine infusion had been a week-and-a-half before his death.
The medical examiner concluded that the traces of ketamine found in his stomach could not have been from his last infusion, as it would only have been in his system for three to four hours.
The report could not specify an 'exact method of intake', noting that there were no new needle marks found on Perry's body to indicate an injection.
According to the report, the ketamine in Perry's body would have overstimulated his heart and depressed his breathing, causing him to 'lapse into unconsciousness' before he slipped below the water in his hot tub.
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The autopsy states that Perry had been sober for 19 months at the time of his death, with no known substance abuse relapses since then.
Investigators found no alcohol, illicit drugs or drug paraphernalia at the scene.
Witnesses said they saw Perry playing pickleball hours before his death, and that those who knew him said he'd been in 'good spirits' in the days before he died.
Featured Image Credit: Mike Pont/WireImage NBCTopics: Matthew Perry