Is nicotine important to tobacco smoking?

Tobacco smoking is generally regarded as a form of nicotine dependence, but the evidence for this is slender. Two experiments are described here which examine the hypothesis that habitual smokers need nicotine and that they regulate their intakes of this drug. A laboratory test for smoking was devised which permitted the continuous monitoring of puffing as well as of selected physiologic variables; the procedure was also designed to reduce the influence of smoking habits and rituals. In the first experiment, inhaled amounts of tobacco smoke reduced subsequent ad libitum smoking in a dose-related way. In the second experiment comparable doses of nicotine were given intravenously to the same subjects, but they failed to affect ongoing smoking. However, both the inhaled and intravenous doses of the drug produced very similar physiologic effects. These experiments do not, therefore, support the nicotine-dependence hypothesis; thus the ways, if any, in which this drug sustains the tobacco-smoking habit merit further examination.