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.
This story is from the {{IssueName}} edition of {{MagazineName}}.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.
Already a subscriber ? Sign In
This story is from the {{IssueName}} edition of {{MagazineName}}.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.
Already a subscriber? Sign In
GUNN SHOW
Arteta's men run riot in Portugal to get CL campaign back on track
BLANK CATS
Sunderland held in yet another stalemate for the Baggies
BREATHING CLASSIC FIRE!
Boss Mac says Dragons are rebuilt and ready to go after their new signings have made up for a sad end to the season that had promised so much
MAUL OR NOTHING
Earl feeling the pain after England's tough autumn but is desperate to deliver success in the Six Nations
Their young lives should be driving force for change
Tragedy 'has united community'
Wake up! The river's gone
Hero of Pontypridd floods re-enacts her gloved mercy dash
'Miss' is still a big hit
1950s teacher & pupils meet up every year
Trump's trade war on drugs
President-elect's vows to hit Canada & Mexico with tariffs
Rod the Glasto legend
Rocker confirmed in Legend slot
I back the royals..but some are not as great as others
Wedding guest James praises 'important' family