The general rule of thumb is that around a quarter of quitters put on five pounds or less, half add between five and 15, and the rest gain more, says nicotine researcher Cynthia S. Pomerleau, PhD, author of the new book Life After Cigarettes. The reason: Nicotine, which suppresses appetite and increases metabolism, is out of your system. To keep pounds in check, don't quit right before your period, when you're prone to bloating; this can be discouraging, Pomerleau says. Another trick: Skip the alcohol. Full of empty calories, it chips away at your resolve to stay smoke-free. Ask your doc about nicotine replacement products or the drug Zyban to help you kick the habit. "Both methods curb weight gain," Pomerleau says, "and they help you get past the initial period of intense craving for a cigarette."