The police in Los Angeles are working with the Drug Enforcement Administration to investigate the source of the ketamine that caused the death of the actor Matthew Perry in October, the authorities said on Tuesday.

The inquiry began after investigators determined that ketamine, an anesthetic with psychedelic properties, was the cause of Mr. Perry’s death, Capt. Scot Williams of the Los Angeles Police Department said in a brief interview.

The Los Angeles County medical examiner’s office said in an autopsy report released on Dec. 15 that Mr. Perry had died of “acute effects of ketamine.” The actor, who gained sitcom superstardom as Chandler Bing on the show “Friends,” was discovered “floating face down” in the heated end of a pool at his home in Los Angeles.

Captain Williams said investigators would seek to discover whether the ketamine was obtained legally. TMZ reported earlier that the authorities were still looking into the source of the ketamine.

Ketamine, a powerful anesthetic, is increasingly used as an alternative therapy for depression, anxiety and other mental health problems. It is also used recreationally.

The autopsy report said that Mr. Perry had been on ketamine infusion therapy, but it determined that the ketamine in his system could not have been from his last known therapy session, about a week and a half before he died. The autopsy said that the level of ketamine found in Mr. Perry’s blood was equivalent to the amount that would be used during general anesthesia.

Mr. Perry had a history of drug and alcohol addiction, which he wrote about in a memoir.

The medical examiner’s office said that drowning, coronary artery disease and buprenorphine, which is used to treat drug addiction and for pain, had contributed to his death.