He said: "I gave up the Sunday before I turned 34. I spent the whole day with a packet of cigarettes. I didn't really see anyone and with every cigarette I smoked. I smoked with as much awareness as I could. And then I wrote a little letter to tobacco.
"It said the usual, 'I remember the first time we met and all that we've been through together. That time you helped me through such-and-such a situation…' and yada-yadda.
PHOTOS - Visit Colin Farrell's profile page for photos, stories and more
Actor Colin Farrell slams spoiled Hollywood stars
Exclusive: Colin Farrell’s ‘Fright Night’ excels 1980s original
"It was very much the kind of letter you'd write to a person you were breaking up with. Because that's what it was – a break-up. It was the first time I'd ever broken up via letter, so it was strange."
It had previously been claimed that Colin tried to give up smoking by having a customized-suit made containing nicotine patches and while the actor admits it would have been a "genius" idea, he insists there is no truth in the rumor.
He told Shortlist magazine: "I once heard that I had a Nicorette patch suit made for 'Miami Vice'. I was trying to give up cigarettes at the time, and apparently the way I did that was to line the inside of a suit with Nicorette patches.
"This was apparently how I was mainlining my nicotine. Which is actually kind of a genius idea when you think about it. But of course, one would overdose on nicotine poisoning around about Take 1. Can you imagine, 'We've lost Farrell. Death by cigarette – and he didn't even inhale.' "