Matthew Perry's parents have claimed that his doctor is the "most culpable of all" in his death.

The Friends star's mother Suzanne and stepfather Keith Morrison, along with his father and stepmother, John and Debby Perry, submitted emotional impact statements ahead of the sentencing of Dr Salvador Plasencia, who has admitted providing ketamine to the actor prior to his death in October 2023.

In July, Plasencia pleaded guilty to distributing ketamine to Perry, who died in the jacuzzi at his Los Angeles home aged 54. His death was attributed to the acute effects of the drug, with drowning and coronary artery disease listed as contributing factors.

Plasencia had entered into a plea deal the previous month and is one of five people facing criminal charges in relation to the actor's death.

In a new victim statement filed before sentencing, Suzanne and Keith opened up about their grief.

"How do you measure grief? Can you possibly provide any rational accounting? The bottom falling out? Yes, that," they wrote, via Rolling Stone. "Here was a life so entwined with ours and held aloft sometimes with duct tape and bailing wire, with anything that might keep that big terrible thing from killing our first-born son, and our hearts with him."

They continued, "And then those greedy jackals come out of the dark, and all the effort is for naught; it all crashes down."

In their letter, they labelled Plasencia "among the most culpable of all".

Meanwhile, John and Debby addressed the doctor directly in their statement, writing, "Matthew's recovery counted on you saying NO."

They added, "We ask the court to give you plenty of time to think about your actions by extending your sentence beyond the mandatory time."

According to Plasencia's plea agreement, he admitted distributing 20 vials of ketamine, ketamine lozenges and syringes to Perry and the actor's personal assistant, Kenneth Iwamasa, between 30 September and 12 October 2023, as previously reported by ABC News.

Plasencia is set to be sentenced on Wednesday.