Irish actor Colin Farrell has revealed his major regret was mentioning his heroin use in a 2004 Playboy interview.

In a new interview in GQ, Farrell says his casual remark about using the lethal drug came back to haunt him.

“You have to be careful, because you know in Playboy I talked about a particular drug I had used once, and I said the line "it seemed like a good idea at the time."

"I wasn't saying that it was ever a good idea, but years later I was coming out of a 7-Eleven  in Los Angeles and I bumped into a gentleman who was without a home, [living] on the streets. And he said to me, "Colin Farrell? Oh man, big fan. You're the reason I did," – and he mentioned the drug.

"He wasn't angry with me.

"He just said,'"I read a Playboy interview you did and you said it 'seemed like a good idea at the time."

“It was on Vermont avenue in Los Feliz where I live, about six years ago. I remember getting into my car and going, I know we all say 'I don't want to be an example' and I certainly would never hold myself up as an example, but to not know that at times people are going to get swayed [anyway]."

In the particularly candid interview, the now sober actor spoke of his affection for children and in true Farrell fashion said that he'd be "f***ed" if he wouldn't be the constant presence in his children's lives and would avoid the negative Hollywood cliché of the absent parent.

"My best advice? Just turn up," he said.

"Just be there. In being there you can make loads of mistakes – any mistakes you make as a parent are pretty much fine, but the worst mistake you can make is to not be there. I have to be careful, because actors are people who work on the road, to not just spend my life in hotels and away.

"I've had years where I've been more successful and less successful at that. But I've read enough stories and I've heard voiced from certain children of actors in the past, 'Well, they weren't really around."

And I'll be f***** if that's going to happen to me. I say that not as judgment – I see how it can happen, because you get into a habit of working and you want to make hay while the sun shines and you have to provide for people.

"But I think at the same time, regardless of what you do or how busy you may be, if you just turn up that's a huge thing."