"Ketamine is a powerful anesthetic that has become increasingly popular as an alternative therapy for depression, anxiety, post-traumatic stress disorder..."

"... and other hard-to-treat mental health problems. It is also used recreationally. The autopsy report said that Perry had been on ketamine infusion therapy but that the ketamine in his system could not have been from his last known therapy session, which was about a week and a half before he died.... 'At the high levels of ketamine found in his postmortem blood specimens, the main lethal effects would be from both cardiovascular overstimulation and respiratory depression,' the autopsy report said. It noted that the level of ketamine investigators found in Perry’s blood was equivalent to the amount that would be used during general anesthesia. The Food and Drug Administration issued an alert in October warning about the dangers of treating psychiatric disorders with compounded versions of the drug...."

From "Matthew Perry Died of ‘Acute Effects of Ketamine,’ Autopsy Says/The medical examiner said drowning, coronary artery disease and the effects of an opioid also contributed to the death of the 'Friends' actor, who was found in a hot tub in October" (NYT).

ADDED: Here's Joe Rogan promoting the stuff 2 months ago.

AND: From "Matthew Perry denounced ketamine in his memoir, said it made him think he was ‘dying’" (NY Post):

Describing the drug as a “giant exhale,” [he] said he would receive ketamine while blindfolded and listening to music. He explained that he would “disassociate” during his infusions and often felt as if he were “dying.” “‘Oh,’ I thought, ‘This is what happens when you die,'” he recalled....