Officials have announced Matthew Perry’s cause of death as “acute effects of ketamine,” along with drowning, coronary artery disease and buprenorphine (an opioid) effects.

Perry — reportedly clean from drugs for 19 months before his tragic passing on Oct. 28 — was undergoing “ketamine infusion therapy” at the end of his life, according to the LA County Medical Examiner’s Office.

But what is ketamine?

Ketamine is a dissociative anesthetic, meaning it makes patients feel detached from their pain and environment.

It can lead users to feel calm and relaxed, become immobile, act as a pain reliever, cause amnesia and provide hallucinogenic effects in certain dosages.

The hallucinogenic has long been abused recreationally as a “club drug” and to facilitate sexual assault, but it has also been recognized for its medical and healing properties much more recently.

The drug has been legal in the United States as an injectable, short-acting anesthetic since the 1970s.

Experts have been experimenting with the drug for years.

In 2019 the Food and Drug Administration (FDA) approved Spravato, a nasal spray version of the narcotic, for treatment-resistant depression. The drug is only available at a certified doctor’s office or clinic.

Ketamine targets the brain chemical messenger glutamate, thought to be connected to both pain and depression.

Experts are unsure whether the psychedelic experience is part of the drug’s therapeutic effect, but some consider it essential to the healing process.

Prescriptions for ketamine have skyrocketed in recent years thanks to for-profit clinics, telehealth services and celebrity endorsements.

Big names including Elon Musks, Chrissy Teigen, Sharon Osbourne, Lamar Odom and Pete Davidson have touted the benefits of ketamine therapy to help with everything from depression to managing addiction.

The generic drug can be purchased cheaply and prescribed by most physicians and some nurses, regardless of their training.

Requests for the drug have spiked so drastically, the FDA has been struggling with shortages of manufactured ketamine for several years.

People have turned to ketamine in place of opioids as the opioid crisis ravages the country, but experts warn that the current ketamine craze — despite the limited research proving its effectiveness — may lead to a similar drug crisis.

The FDA has warned against freely available versions of ketamine, including nasal sprays, lozenges and pills, noting that the federal agency does not regulate the products and cannot guarantee their safety.