Intended for healthcare professionals


E-cigarettes can help people quit smoking but more evidence needed on long term harms, review concludes

BMJ 2020; 371 doi: (Published 14 October 2020) Cite this as: BMJ 2020;371:m3982
  1. Jacqui Wise
  1. London

An updated Cochrane review has concluded that electronic cigarettes containing nicotine could increase the number of people who successfully stop smoking compared with other approaches such as nicotine gum or patches.1 The review authors did not detect any clear evidence of serious harms from nicotine e-cigarettes but said that more evidence was needed.

In September the Committee on Toxicity of Chemicals in Food, Consumer Products, and the Environment concluded that e-cigarettes were significantly less harmful than smoking but were not risk-free.2 In 2015 a review commissioned by Public Health England, which concluded that e-cigarettes were 95% less harmful than tobacco, led to widespread criticism with many questioning the evidence and the authors’ conflicts of interest.3

The updated Cochrane review included 50 studies with a total of 12 430 participants—an increase of 35 studies since the previous review published in 2016; 26 of the studies were randomised controlled trials. It found moderate certainty evidence from three studies with 1498 participants that quit rates were higher in those randomly assigned to receive e-cigarettes compared with nicotine replacement (risk ratio 1.69, 95% confidence interval 1.25 to 2.27). This might translate to an additional four people per 100 who could quit smoking by using nicotine e-cigarettes.

Another three studies, involving 892 people, found that quit rates were higher in patients randomly selected to receive nicotine e-cigarettes compared with non-nicotine e-cigarettes (1.71, 1.00 to 2.92). This evidence was also of moderate certainty, the authors said.

Evidence from four studies, involving 2312 people, showed that more people who used nicotine e-cigarettes quit smoking than those who received only behavioural support or no support. If four people in 100 quit with no support, an additional six people in 100 might quit by using nicotine e-cigarettes. But the review said that this finding was very low certainty, owing to issues with imprecision and risk of bias.

The review found that the overall incidence of adverse effects was low across all study arms, but the longest follow-up was two years and the overall number of studies was small. The studies assessed the potential harm of e-cigarettes when used to help people quit smoking, so did not assess other potential harms such as whether e-cigarettes encouraged nicotine use among people who did not smoke.

Jamie Hartmann-Boyce from the Cochrane Tobacco Addiction Group, lead author on the study, said, “While there is currently no clear evidence of any serious side effects, there is considerable uncertainty about the harms of electronic cigarettes, and longer term data are needed. Scientific consensus holds that electronic cigarettes are considerably less harmful than traditional cigarettes, but not risk-free.”

She added, “Modern electronic cigarette products have better nicotine delivery than the early devices that were tested in the trials we found, and more studies are needed to confirm whether quit rates are affected by the type of electronic cigarettes being used.”

John Britton, emeritus professor of respiratory medicine at Nottingham University, commented, “This comprehensive review of all data on the efficacy of electronic cigarettes in helping people to quit provides definitive confirmation that electronic cigarettes offer smokers an effective means of quitting, and perhaps even more so than some licensed stop smoking medicines.”


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