Some abstinent smokers develop withdrawal symptoms when they stop using nicotine gum or when placebo is substituted; thus, physical dependence on nicotine gum does occur. Some smokers also use nicotine gum beyond the recommended period; thus, behavioral dependence on the gum occurs. Many (7-41%) smokers misuse nicotine gum by smoking cigarettes and chewing the gum concurrently. Among smokers who stop using the gum, many (35-90%) do not stop gum use by the recommended 3 months, and a substantial percentage (13-38%) persist in gum use for 1 year. Among quitters, long-term use of nicotine gum appears to be greater than that of placebo gum. If rapidity of onset and frequency of use are determinants of dependence potential, then nasal sprays and aerosols but not nicotine patches should have dependence potential. There are no reports of misuse of the gum by non-smokers; thus, the gum appears to have little if any abuse liability.