From The Paris Review interview archive: Kurt Vonnegut discusses quitting smoking and then starting again and then quitting and then stating again–
INTERVIEWER: Have you ever stopped smoking?
VONNEGUT: Twice. Once I did it cold turkey, and turned into Santa Claus. I became roly-poly. I was approaching two hundred and fifty pounds. I stopped for almost a year, and then the University of Hawaii brought me to Oahu to speak. I was drinking out of a coconut on the roof of the Ili Kai one night, and all I had to do to complete the ring of my happiness was to smoke a cigarette. Which I did.
INTERVIEWER: The second time?
VONNEGUT: Very recently—last year. I paid Smokenders a hundred and fifty dollars to help me quit, over a period of six weeks. It was exactly as they had promised—easy and instructive. I won my graduation certificate and recognition pin. The only trouble was that I had also gone insane. I was supremely happy and proud, but those around me found me unbearably opinionated and abrupt and boisterous. Also: I had stopped writing. I didn’t even write letters anymore. I had made a bad trade, evidently. So I started smoking again. As the National Association of Manufacturers used to say, “There’s no such thing as a free lunch.”