The 37-year-old actor used to regularly drink alcohol and take drugs but realised he had a problem when he deliberately harmed himself just to show people he was tough at a party, the Hollywood Reporter said.
"I was at a party, and deliberately bashed my head on the concrete floor. Like, 'Hey, look how tough I am!' I did it again. And I spent the night at St. Vincent's Hospital with a sock of ice, waiting for them to stitch me up," Cooper said.
Following the incidents, the actor decided to completely quit drugs and alcohol eight years ago and says it was a turning point for him.
"I don't drink or do drugs anymore. Being sober helps a great deal. I remember looking at my life, my apartment, my dogs when I was still using, and I thought, 'What's happening?' I was so concerned what you thought of me, how I how I was coming across, how I would survive the day.
"I always felt like an outsider. I just lived in my head. I realised I wasn't going to live up to my potential, and that scared the hell out of me. I thought, 'Wow, I'm actually gonna ruin my life. I'm really gonna ruin it'," Cooper said.