E-cigarettes and smoking cessation. Similar efficacy to other nicotine delivery devices, but many uncertainties.

E-cigarettes, marketed as an alternative to conventional cigarettes, are designed to transform a solution of variable composition, with or without nicotine, into an aerosol that the user inhales. How effective are e-cigarettes as an aid to smoking cessation, and what are their known adverse effects? To answer these questions, we conducted a review of the literature using the standard Prescrire methodology. A randomised trial involving 657 individuals who wanted to stop smoking compared e-cigarettes (with or without nicotine) with nicotine patches. There was no difference between the groups after 6 months, with an overall quit rate of about 5%. A double-blind randomised trial including 300 smokers compared the impact of e-cigarettes with or without nicotine on tobacco consumption. After 3 months, 14% of those using e-cigarettes with nicotine had quit completely, compared to 4% of those using e-cigarettes without nicotine. Adverse events reported in these trials were mild and transient, and mainly included dry mouth, irritation of the mouth and throat, dizziness, and nausea. When the solution ("e-liquid") contains nicotine, the main adverse effects are those of nicotine. Bronchial disorders, neuropsychiatric disorders and ocular irritation have been reported with inhaled propylene glycol. The effects of propylene glycol and glycerol, when heated and inhaled over long periods, are not known. The addictive effect is difficult to determine. Long-term use of e-cigarettes has been observed in about one-third of people who stopped smoking. Toxic or carcinogenic substances have been found in some e-cigarette aerosols, but at lower concentrations than in tobacco smoke. The diversity in the composition of e-liquids and the lack of proper controls make it difficult to assess the associated dangers. In early 2015, e-cigarettes containing nicotine appear to have efficacy similar to that of other nicotine delivery systems as an aid to smoking cessation. Apart from the effects of nicotine, there are few known adverse effects. However, there are many uncertainties as to the composition of the different e-liquids and the long-term effects of the substances when they are heated and inhaled. There is no reason to discourage smokers from substituting the proven, serious harms of tobacco smoke with the potential and poorly defined harms associated with e-cigarettes.