Beloved “Friends” star Matthew Perry, who played Chandler Bing on one of TV’s longest running and most iconic series, died from the acute effects of the anesthetic ketamine, according to his autopsy, released Friday.

Drowning “in the heated end of his pool” also contributed to the 54-year-old actor’s death, deemed an accident, the Associated Press reported Friday, citing the Los Angeles County Department of Coroner. Coronary artery disease and buprenorphine, used to treat opioid use disorder, also reportedly contributed to his death.

Perry was declared dead after being found unresponsive at his home in the Pacific Palisades area of Los Angeles on Oct. 28. While the actor had previously taken drugs, he had been “reportedly clean for 19 months,” according to the coroner’s report. He had reportedly received ketamine infusion therapy for depression and anxiety, the coroner wrote. But his last treatment was reported to have occurred a week and a half before his death.

Perry had reportedly played pickleball earlier in the day. His assistant, who found him face down in the pool after returning from running errands, told investigators that the actor hadn’t been sick, made any health complaints, or shown evidence of recent alcohol or drug use.

Ketamine, popularly known as the party drug Special K, has recently been hailed as a breakthrough treatment for major depression, but it is not without risks.

What is ketamine?

Ketamine is an anesthetic used by medical providers and veterinarians with some hallucinogenic effects, according to the U.S. Drug Enforcement Administration. A dissociative drug similar to psychedelics like nitrous oxide, it makes users feel detached from their pain, as well as their environment, distorting perception of sight and sound.

What is ketamine approved to treat?

It’s been approved by the U.S. Food and Drug Administration, in low doses, for use as a short-acting anesthetic in humans and animals, and as a nasal spray (esketamine) for treatment-resistant depression in conjunction with another oral antidepressant, according to the DEA. It’s a fast-acting antidepressant, used to bridge the gap while waiting for SSRIs to kick in, which can take weeks.

Can ketamine be used for depression?

Ketamine is only FDA approved for use as a nasal spray in treatment-resistant depression. But it’s increasingly used “off label” for treating depression, suicidal ideation, and chronic pain, according to the U.S. National Institutes of Health’s National Library of Medicine. An increasing number of clinics offer infusions for the treatment of depressions. Patients are monitored during and after the infusion.

Is it possible to abuse ketamine?

It can be used illegally to get high—via an injectable, liquid mixed with other liquids, or a powder to be snorted, mixed in drinks, or smoked. On the street it’s sometimes known by the names Cat Tranquilizer, Cat Valium, Jet K, Kit Kat, Purple, Special K, Special La Coke, Super Acid, Super K, Horse Trank, and Vitamin K. An overdose can lead to loss of consciousness and dangerously slowed breathing, according to the DEA.

Users often partake of it with other drugs like Ecstasy (called “kitty flipping”), or cocaine, or sprinkle it on marijuana blunts, according to the Nemours Children’s Health system. It can also be smoked with tobacco.

The trip, called the “K hole,” usually lasts 2 hours or less. During this time, users may become nauseated, vomit, and/or have thinking and memory problems. High doses may cause movement issues, body numbness, and slowed breathing.

What are signs of a ketamine overdose?

Potential side effects of an overdose include respiratory failure and death.

Should ketamine and buprenorphine be used together?

Perry reportedly had buprenorphine—a medication approved by the FDA to treat Opioid Use Disorder—in his system, in addition to ketamine. Using the two drugs together poses a “major” risk and can increase side effects like “dizziness, drowsiness, confusion, difficulty concentrating, excessive sedation, and respiratory depression,” according to Drugs.com. It advises users of both to “avoid activities requiring mental alertness such as driving, operating hazardous machinery, or engaging in potentially hazardous activities until you know how the medications affect you.”

The Associated Press contributed to this report.

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Original: Fortune | FORTUNE: What is ketamine? What to know about the drug that killed ‘Friends’ star Matthew Perry