An alkaloid, which is the major psychoactive substance in tobacco. It has both stimulant and, subjectively, relaxing effects. It produces an alerting effect in some individuals, an increased capacity to focus attention. In others, t reduces anxiety and irritability. Nicotine is used in the form of inhaled tobacco smoke, ‘smokeless tobacco’ (such as chewing tobacco), snuff, nicotine gum, or as an adhesive patch worn on the skin.