Matthew Perry Cause of Death, 'Acute Effects of Ketamine'

Matthew Perry died from "the acute effects of ketamine," a drug that is used to treat depression and is also used as a recreational drug.

The Los Angeles County Medical Examiner's Office just released the toxicology report, concluding Perry had taken ketamine infusion therapy for depression and anxiety a week-and-a-half before his death. The ketamine in his system at the time of his death, however, "could not be from that infusion therapy, since ketamine's half-life is 3 to 4 hours, or less."

According to the Medical Examiner, the ketamine in Perry's system caused both cardiovascular overstimulation and respiratory depression.

The M.E. found no evidence of alcohol, methamphetamine, cocaine, heroin, PCP or fentanyl.

The contributory factors in Perry's death included drowning, coronary artery disease, and buprenorphine effects. Buprenorphine is used to ween addicts off opioids.

What's interesting ... according to the M.E., Perry had been undergoing ketamine infusion therapy every other day for some time, but 6 months before he passed, a new doctor decided Perry was doing well enough that he didn't need the treatment that often. The report does not say how frequently Perry was getting ketamine infusion therapy in the months before he died.

Although smoking was not listed as a contributing factor in Perry's death, the report notes he smoked 2 packs of cigarettes a day, had COPD/emphysema and diabetes.

And the M.E. says based on their interviews, Perry was clean and sober for 19 months.

TMZ broke the story ... on Oct. 28, Matthew was found unresponsive in his jacuzzi after playing 2 hours of pickleball at Riviera Country Club near his home in Pacific Palisades. First responders rushed to the property on a cardiac arrest call, and he was declared deceased on the scene after an apparent drowning.

While Matthew was open about his history of substance abuse, no illicit narcotics were found at his home.

Like we told you ... Matthew had played pickleball in the morning for a couple hours before returning home and sending his assistant on an errand. Sometime later, the assistant returned, discovered MP in the hot tub and then called 911.

Matthew's death sent shockwaves through Hollywood ... with tributes pouring in and tons of celebs honoring him and paying tribute.

As we first reported ... sources in daily contact with the late "Friends" star told us he had never been happier in the time leading up to his passing, committing to a new movie and loving the new home he had moved into just 3 weeks before he died there.