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.