E-cigarettes--prevention, pulmonary health, and addiction.

BACKGROUND E-cigarettes are coming into wider use. They are advertised as an aid to smoking cessation, but there is concern that they may also serve as a gateway drug for cigarette smoking. METHOD The authors systematically searched the PubMed database for relevant publications on the mechanism of action of e-cigarettes, the nature of their emissions, their assessment by potential users, their efficacy in smoking cessation, and their potential for addiction. RESULTS There have been many reports of epidemiologically uninformative case series in which smokers were helped to stop smoking by the use of e- cigarettes. Only two controlled trials have shown that e-cigarettes have approximately the same effect as nicotine substitution therapy when used as an aid to smoking cessation. The effect is nearly independent of nicotine content. E-cigarettes are also consumed, to a small extent, by nonsmokers. As far as can be estimated toxicologically at present, the danger to active and passive smokers of e-cigarettes is presumably orders of magnitude less than that of tobacco smokers, although the variable composition of the fluids used in e-cigarettes introduces a degree of uncertainty. CONCLUSION Preclinical and initial clinical data, including some data from randomized controlled trials, indicate that e-cigarettes may be useful as an aid to smoking cessation or as a means of lowering risk in high-risk groups. In contrast to the demonstrated efficacy of multimodal smoking-cessation programs with pharmacological and psychotherapeutic support, the efficacy of e-cigarettes in smoking cessation has not yet been satisfactorily shown. Valid and informative clinical trials are urgently needed. These should also be designed to determine what predisposition(s), if any, might make the use of e-cigarettes more or less successful than that of other aids to smoking cessation. Moreover, e-cigarettes might be a gateway drug for cigarette smoking; thus, no clear recommendation about their use can be made at present.