Detailing the extent of his highly-publicised addiction in a rare interview, the actor, 53, revealed that he 'nearly died' aged 49 when his colon burst after opioid overuse.
As a result, Matthew suffered a gastrointestinal perforation and spent two weeks in a coma and five months in hospital, and had to use a colostomy bag for nine months.
He told People, 'The doctors told my family that I had a 2 per cent chance to live. I was put on a thing called an ECMO machine, which does all the breathing for your heart and your lungs. And that’s called a Hail Mary. No one survives that.'
Fortunately, Matthew - who first admitted himself to rehab when he became addicted to Vicodin after a jet ski accident in 1997 - has come out the other side and describes himself as a 'pretty healthy guy right now.' He has not revealed how long he has been sober, but has been counting every day.
The 17 Again star started heavily drinking when he joined the cast of Friends in 1994, and previously said he doesn't remember filming three years of the show.
'Season nine was the year that I was sober the whole way through,' he explained. 'And guess which season I got nominated for best actor? I was like, "That should tell me something."'
At his lowest, Matthew - who in total has been to rehab 15 times - was taking 55 tablets a day and weighed just over 9stone.
14 scars on his stomach, as well as the thought of using a colostomy bag, serve as a reminder to not take Oxycotin again, as Matthew said, 'All I have to do is look down.'
And now, he hopes that his memoir, set to hit bookshelves on November 1, will help others grappling with addiction.