What are electronic cigarettes?
Electronic cigarettes (e-cigarettes) are handheld devices that work by heating a liquid that usually contains nicotine and flavourings. E-cigarettes allow you to inhale nicotine in a vapour rather than smoke. Because they do not burn tobacco, e-cigarettes do not expose users to the same levels of chemicals that can cause diseases in people who smoke conventional cigarettes.
Using an e-cigarette is commonly known as ‘vaping’. Many people use e-cigarettes to help them to stop smoking tobacco. In this review we focus primarily on nicotine e-cigarettes.
Why we did this Cochrane Review
Stopping smoking lowers your risk of getting lung cancer, heart attacks and many other diseases. Many people find it difficult to stop smoking. We wanted to find out if using e-cigarettes could help people to stop smoking, and if people using them for this purpose experience any unwanted effects.
What did we do?
We searched for studies that looked at the use of e-cigarettes to help people stop smoking.
We looked for randomized controlled trials, in which the treatments people received were decided at random. This type of study usually gives the most reliable evidence about the effects of a treatment. We also looked for studies in which everyone received an e-cigarette treatment.
We were interested in finding out:
· how many people stopped smoking for at least six months; and
· how many people had unwanted effects, reported on after at least one week of use.
Search date: We included evidence published up to 1st May 2021.
What we found
We found 61 studies in 16,759 adults who smoked. The studies compared e-cigarettes with:
· nicotine replacement therapy, such as patches or gum;
· varenicline (a medicine to help people stop smoking);
· nicotine-free e-cigarettes;
· other types of nicotine-containing e-cigarettes (e.g. pod devices, newer devices);
· behavioural support, such as advice or counselling; or
· no support for stopping smoking.
Most studies took place in the USA (26 studies), the UK (11), and Italy (7).
What are the results of our review?
More people probably stop smoking for at least six months using nicotine e-cigarettes than using nicotine replacement therapy (4 studies, 1924 people), or nicotine-free e-cigarettes (5 studies, 1447 people).
Nicotine e-cigarettes may help more people to stop smoking than no support or behavioural support only (6 studies, 2886 people).
For every 100 people using nicotine e-cigarettes to stop smoking, 9 to 14 might successfully stop, compared with only 6 of 100 people using nicotine-replacement therapy, 7 of 100 using nicotine-free e-cigarettes, or four of 100 people having no support or behavioural support only.
We are uncertain if there is a difference between how many unwanted effects occur using nicotine e-cigarettes compared with nicotine replacement therapy, no support or behavioural support only. There was some evidence that non-serious unwanted effects were more common in groups receiving nicotine e-cigarettes compared to no support or behavioural support only. Similar low numbers of unwanted effects, including serious unwanted effects, were reported for other comparisons. There is probably no difference in how many non-serious unwanted effects occur in people using nicotine e-cigarettes compared to non-nicotine e-cigarettes.
The unwanted effects reported most often with nicotine e-cigarettes were throat or mouth irritation, headache, cough and feeling sick. These effects reduced over time as people continued using nicotine e-cigarettes.
How reliable are these results?
Our results are based on a small number of studies, and in some the data varied widely.
We are moderately confident that nicotine e-cigarettes help more people to stop smoking than nicotine replacement therapy or nicotine-free e-cigarettes. More studies are still needed to confirm this.
Studies comparing nicotine e-cigarettes with behavioural or no support also showed higher quit rates in people using nicotine e-cigarettes, but provide less certain data because of issues with study design.
Most of our results for the unwanted effects may change when more evidence becomes available.
Nicotine e-cigarettes probably do help people to stop smoking for at least six months. They probably work better than nicotine replacement therapy and nicotine-free e-cigarettes.
They may work better than no support, or behavioural support alone, and they may not be associated with serious unwanted effects.
However, we need more evidence to be confident about the effects of e-cigarettes, particularly the effects of newer types of e-cigarettes that have better nicotine delivery than older types of e-cigarettes.
There is moderate-certainty evidence that ECs with nicotine increase quit rates compared to NRT and compared to ECs without nicotine. Evidence comparing nicotine EC with usual care/no treatment also suggests benefit, but is less certain. More studies are needed to confirm the effect size . Confidence intervals were for the most part wide for data on AEs, SAEs and other safety markers, with no difference in AEs between nicotine and non-nicotine ECs. Overall incidence of SAEs was low across all study arms. We did not detect evidence of harm from nicotine EC, but longest follow-up was two years and the number of studies was small.
The main limitation of the evidence base remains imprecision due to the small number of RCTs, often with low event rates, but further RCTs are underway. To ensure the review continues to provide up-to-date information to decision-makers, this review is now a living systematic review. We run searches monthly, with the review updated when relevant new evidence becomes available. Please refer to the Cochrane Database of Systematic Reviews for the review’s current status.