He said: "I drink at times too much. I do enjoy drinking, and there have been times in my life when it's crossed the line from being fun to having to drink late at night for absolutely no reason. So what I do is, I stop."
The Oscar nominee also admits he has tried cocaine in the past but didn't like it.
He revealed: "I didn't have an issue with it. I'm not a big druggie, not at all. Blow is absolutely a nonstarter."
At the same time he says he has trouble getting to sleep because he is an over-thinker.
The actor - who has dated a string of beautiful women including Lisa Snowdon, Elisabetta Canalis and Stacy Keibler - admits he hasn't had a peaceful night's sleep in a long time.
He said: "Turning off the television causes me to think, and once I start that vision roaring, I have a very tough time getting to sleep. I'm able to numb out. Without question, I wake every night five times."
Despite his popularity with women, Clooney admits that his famous lifestyle can be isolating.
He continued: "Anyone would be lying if they said they didn't get lonely at times. The loneliest you will get is in the most public of arenas: you will go to a place and end up in the smallest compartment possible, because it's a distraction to everybody, and you end up not getting to enjoy it like everyone else."
He added in a frank interview with The Hollywood Reporter: "I have been infinitely more alone in a bad relationship; there's nothing more isolating. I have been in places in my life where that has existed."
The screen star confessed he had been "left for someone; all those things. And it was sometimes a surprise, and sometimes you saw it coming. The most painful was when I kept trying to get (one woman) back. But we all make dumb mistakes."
The 50-year-old also spoke about how friend Brad Pitt 'outed' him as gay as a joke.
He reflected: "A couple of years ago, [he] really nailed me. He did one of those shows and they asked him when he was going to marry Angie [Angelina Jolie], and he said, 'I'll marry when George can legally marry [a man]'."
He went on: "He really got me badly, something I have had to deal with the past few years. But I could give a s***."
> George Clooney, Brad Pitt, Meryl Streep: Oscars nominees bash pictures
> George Clooney: 'Descendants wardrobe nearly killed my masculinity'
Watch the Descendants trailer below: