The Hangover actor said that he got sober at the age of 29, as his partying lifestyle had left him feeling destructive and depressed.
"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?'" Cooper explained to The Hollywood Reporter.
"I was so concerned what [people] thought of me, 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 - now aged 37 - also recalled a particularly scary experience when his alcohol and drug use caused him physical injury, saying: "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 recently entered talks to appear in two new films - Clint Eastwood's A Star Is Born remake and J Blakeson's crime thriller Bad Blood and Trouble.