Los Angeles, California - The main doctor charged in connection with the drug overdose of Friends star Matthew Perry is expected to enter a guilty plea in the coming weeks, the US Justice Department said Monday.

Salvador Plasencia "has agreed to plead guilty to four counts of distribution of ketamine, which carries a statutory maximum sentence of 40 years in federal prison," the department said in a statement.

The second doctor in the case, Mark Chavez, pleaded guilty last October to conspiring to distribute ketamine in the weeks before the actor was found dead in the hot tub of his Los Angeles home in 2023.

Perry's lengthy struggles with substance addiction were well-documented, but his death at age 54 sent shockwaves through the global legions of Friends fans.

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A criminal investigation was launched soon after an autopsy discovered he had high levels of ketamine in his system.

Plasencia allegedly bought ketamine off Chavez and sold it to the American-Canadian actor at hugely inflated prices.

"I wonder how much this moron will pay," Plasencia wrote in one text message presented by prosecutors.

He went to Perry's home to administer ketamine by injection, according to the plea deal published by the DOJ.

In total, Plasencia distributed 20 vials of ketamine over a roughly two-week period in autumn 2023, the document said.

Perry had been taking ketamine as part of supervised therapy for depression.

But prosecutors say that before his death he became addicted to the substance, which also has psychedelic properties and is a popular party drug.

Five people have been charged over Perry's death.

Jasveen Sangha, the alleged "Ketamine Queen" who supplied drugs to high-end clients and celebrities, is charged with selling Perry the dose that killed him. She has pleaded not guilty.

Perry's live-in personal assistant and another man pleaded guilty last August to charges of conspiracy to distribute ketamine.