Sean Penn and Robin Wright's son was addicted to crystal meth.
Hopper Penn, 23, agreed to go to rehab to be treated for his problem following an ultimatum from his actor father that would have left him on the streets if he didn't seek help.
He said: "I was pretty bad. I just got caught a lot doing stuff, you know? Whether it was my parents or the cops.
"I was doing a lot of stuff, but meth was the main one that brought me down.
"I went to rehab because I woke up in a hospital and my dad was like, 'Rehab? Or bus bench?' I was like, 'I'll take the bed.' "
And the actor is relieved the "worst time" of his life is now behind him.
He said: "Thank God I got out of that because that was the worst time in my life. Because it's not fun when it gets to a point where you just need it."
Around that time, Hopper's father cast him in his latest directorial effort, 'The Last Face', and the model-and-actor thinks he did so in order to give him some "structure" in his life.
He told ES magazine: "Structure? Yeah. I mean, that could have been it. I know he kind of wrote the part for me, based it on me a little bit.
"He really wanted to work with me and it ended up being great. But yeah, maybe it was about giving me just a little structure, and just trying to get me to get my own thing going."
And Hopper wasn't particularly happy with his performance when he saw a playback of the first take.
He admitted: "[I told him] to recast me, because I just couldn't see myself in pictures, or on-screen.
"Honestly: I didn't think I'd be watching any of my movies, ever.'
But he eventually started to enjoy the experience.
He added: "I thought we were going to butt heads on set but we worked pretty well together, I think, and I had a blast. So since then I've been like, 'This is what I want to do.' "