My dr told me that Zyban may take about a week to work. However, after a few days, I completely lost the urge to smoke. I would still try out of habit, but the cigarettes tasted terrible. I also could not stand the smell of other people smoking. The only problem that I have had is that I started feeling too confident after about a month and a half and quit taking the pill regularly. I then would go out with friends for drinks and would bum a few smokes after a few drinks. I also hate that you have to have a prescription. I have not had any side effects from Zyban and recommend it to anyone who wants to quit smoking.