When he looks back, he shudders at his behaviour, he says.
Interviewer Piers Morgan asks him: "How close did drugs come to killing you, do you think?"
The pop star says: "Very close. I mean, I would have an epileptic seizure and turn blue, and people would find me on the floor and put me to bed, and then 40 minutes later I'd be snorting another line.
"This is how bleak it was, I'd stay up, I'd smoke joints, I'd drink a bottle of Johnnie Walker and then I'd stay up for three days and then I'd go to sleep for a day and a half, get up, and because I was so hungry because I hadn't eaten anything, I'd binge and have like three bacon sandwiches, a pot of ice cream and then I'd throw it up, because I became bulimic and then go and do the whole thing all over again. That is how tragic my life was.
"And I'm not being flippant when I say that, when I look back I shudder at the behaviour and what I was doing to myself...it just takes over your whole psyche, this stuff.
"I never considered myself a drug addict, I thought drug addicts were people who stuck needles in their arms. And I was the biggest junkie there was."
The star renews his attack on TV's The X Factor.
Asked by Morgan why he had described the show as brain crippling and boring, he says: "I can't watch those kind of shows. I find it very disturbing for me from the artists' point of view.
"I'm totally on the artists' side, anybody who appears on the show, whether they've got much talent or not, if they win it, I wonder what's going to become of them – are they just fodder for two years until the next Leona Lewis comes along, or the next Alexandra Burke?
"Why aren't they going on tour? What's happening? They can't survive, I know, by just making records.
"It's the cart before the horse. When I got a record contract in the old days, you had to go on tour to get a record contract. You had to be good live.
"And now you can go on TV and sing well, but you have no real experience of doing shows."