Why is this review important?
Finding out more about the safety and efficacy of electronic cigarettes as a quitting tool is important as smoking is the leading cause of preventable illness and premature death globally, and is not only harmful to those who smoke, but also to the people around them. Stopping smoking lowers your risk of getting lung cancer, heart disease and other serious health conditions. Unfortunately, quitting smoking is very hard and many of the existing tools available to help people quit still result in many people relapsing to smoking.
Cochrane reviews bring together the best available evidence from research and systematically review this information to determine the benefits and risks of treatments. Cochrane Reviews are internationally recognised as the highest standard in evidence-based health care. They are especially important in topics such as this where there is uncertainty in the evidence base that may make public health communication and guideline development difficult.
What the researchers did and what they found
In order keep the information as up to date as possible for health care professionals, policy makers and people who want to stop smoking we search the literature every month for new evidence; this is called a living systematic review. The main outcomes we look at are smoking cessation at six months or longer and side effects at one week follow-up or longer. We include any intervention study in our review, but only randomised trials are included in our main analyses.
Our review includes 61 completed studies representing 16,759 participants, of which 34 are randomised controlled trials. Five new studies have been added since our previous update. Our review now contains evidence up to 1st May 2021.
The review found that there is moderate certainty that nicotine containing electronic cigarettes help more people to quit at six months or longer compared to electronic cigarettes without nicotine or nicotine replacement therapy, such as patches or gum (a well-established treatment for quitting smoking). Substantial uncertainty still exists around nicotine containing electronic cigarettes compared to no intervention (e.g. continued smoking). This is reflected in our assessment of the quality of the evidence, which is considered ‘very low’ according to GRADE standards.
For every 100 people using nicotine e-cigarettes to stop smoking, 9 to 14 might successfully stop, compared with only 6 people using nicotine-replacement therapy, 7 using nicotine-free electronic cigarettes, or 4 people provided with no support or behavioural support only.
We did not detect any clear evidence of harm from electronic cigarettes; however, longest follow-up was two years and the overall number of studies was small.
New outcome: do people continue to use electronic cigarettes long term?
In response to feedback, for the first time in this update, data is included on the proportion of participants still using electronic cigarettes or quitting aids at six months or longer. Data from two studies comparing nicotine electronic cigarettes with nicotine replacement therapy were notably different; one found no difference in the proportion of participants still using study products at longest follow-up, and the other finding significantly higher levels of electronic cigarettes use than nicotine replacement therapy. There was no evidence for a difference in the proportion of people still using electronic cigarettes at longest follow-up in two studies comparing nicotine electronic cigarettes with non-nicotine electronic cigarettes. In many of the uncontrolled studies that measured this outcome, more than half of participants given nicotine electronic cigarettes at the start of the study were still using electronic cigarettes at six months or longer.
We need more, reliable evidence to be confident about the effects of e‐cigarettes, particularly the effects of newer types of e‐cigarettes that have better nicotine delivery.
Sharing the findings
Our aim is to widely disseminate the findings of this review to people who smoke, health care professionals and policy makers in order to help people who smoke to quit and stay quit. We aim to share this information via presentations, social media, briefing documents, and a monthly podcast. See our webpage for links to upcoming talks by lead author Jamie Hartmann-Boyce and our briefing documents, presentations related press coverage and podcasts which are also available on the University of Oxford Podcasts site, iTunes and Spotify.
As data on electronic cigarettes continue to emerge, we will continue to update our analyses to ensure decision makers have the best available evidence to hand when considering the role of electronic cigarettes in supporting smoking cessation. Look out for the next update.