Steve-O was first hospitalised for substance abuse and mental issues in 2008 and pleaded guilty to felony possession of cocaine later that same year.
The Tv and film stuntman also had to enter a mental health facility, but has been sober for the past five years - much to Knoxville's amazement.
He tells The New York Times magazine, "I thought no way would he ever be able to get clean. I've never seen anyone at those depths. He was at the Marianas Trench (deepest part of the ocean) of depravity."