And Kayti Edwards urged police to widen their probe into the actor's ketamine death beyond the five people already charged over it.
The 47-year-old, who Matthew's assistant from 2011, told how things got so bad with his addiction she had to quit the job.
She also claimed he was so desperate at times he was paying thousands of dollars for a £9 vial of ketamine to unscrupulous medics who would dish out the drug with no questions.
In an exclusive Mirror interview, Kayti claimed the actor told her at the height of his addiction: "I'm in with the doctors."
She said: "There's a whole network of people beyond those facing criminal charges who the police need to investigate. Detectives need only delve back into his medical history.
"There are so many more doctors who have been on his books over the years who will be terrified right now.
"Whenever he was in active addiction, he knew instantly where to turn. It's a scandal.
"Matthew paid me very well as his assistant but there came a point for me that he got so bad that I had no choice but to walk away from that salary. But I knew that I could not watch him die. I would never, ever be able to live with myself."
KETAMINE
Matthew's live-in assistant Kenneth Iwamasa and Jasveen Sangha, dubbed the "Ketamine Queen" by prosecutors, are among the five people charged over his death.
Kayti the step-grandaughter of British actress Julie Andrews - dated the Friends star in 2006 before becoming his assistant. They remained friends right up until he died aged 54 in October last year.
She claimed that while his links to doctors go back years, his choice of drugs changed and she was shocked by the sheer quantities he would take.
Kayti said: "Ketamine was his new thing. It all started with unscrupulous doctors oversubscribing prescription pills like Vicodin.
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