Matthew Perry's cause of death was an accident caused by the "acute effects of ketamine", medical officials have ruled.
The Friends star, 54, was found unresponsive in the hot tub of his Los Angeles home in late October.
An initial post-mortem examination was inconclusive, though listed drowning as a contributing factor in his death. Investigators from the L.A. County Medical Examiner's office have now announced he had high levels of ketamine in his system when he died.
"At the high levels of ketamine found in his post-mortem blood specimens, the main lethal effects would be from both cardiovascular overstimulation and respiratory depression," senior deputy medical examiner Raffi Djabourian, according to the Press Association.
"Drowning contributes (to his death) due to the likelihood of submersion into the pool as he lapsed into unconsciousness; coronary artery disease contributes due to exacerbation of ketamine induced myocardial effects on the heart."
Perry's ketamine levels were 3,540 ng/ml - at the top end of the range given to anaesthetise patients undergoing surgery, according to TMZ.com.
The Canadian-American actor was found unresponsive at his home on 28 October. The following day, the Medical Examiner's office deferred his case awaiting further details.
The Medical Examiner's report stated that Perry, who had long battled depression and addiction, had been prescribed ketamine for depression and anxiety.
His funeral was held on 3 November, with his Friends castmates Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matt LeBlanc, and David Schwimmer in attendance.