Wednesday December 17 2014
Millions of people have taken up the 'vaping' habit
“E-cigarettes can help smokers quit or cut down heavily,” The Guardian reports. An international review of the evidence, carried out by the well-respected Cochrane Collaboration, found evidence that they can help some smokers quit.
However, the available body of evidence was slim – just two randomised controlled trials (RCTs), involving around 950 participants.
The two studies found that 9% of people using e-cigarettes with nicotine quit smoking for at least six months, compared to 4% of people using placebo e-cigarettes. However, the results on quitting were only significant when the trials were added together, because so few people managed to quit. The individual trials found no difference in the number of people who quit smoking by at least six months when using e-cigarettes with nicotine compared to placebo e-cigarettes or nicotine patches. The researchers say that the pooled results should therefore be treated with caution.
Another concern is that while e-cigarettes are far safer than “real” cigarettes, they do nothing to tackle the underlying nicotine addiction.
A combination of methods may be the most effective method for people who are keen to stop. Other stop smoking treatments include nicotine gum, patches or inhalers, as well as medication that can reduce cravings, such as Zyban (bupropion).
Where did the story come from?
The study was carried out by researchers from Queen Mary University of London, the University of Auckland and the University of Oxford. There was no external funding.
The study was published in the peer-reviewed online medical journal The Cochrane Database of Systematic Review. As with all Cochrane research, the study has been made available on an open-access basis, so is free to read online or download as a PDF.
There were some inaccuracies in the media reporting of the study. There were not just 662 people in the two RCTs; this was the number of people randomised to have a type of e-cigarette. The actual number of participants was 957, as other people in these two trials were given nicotine patches.
The Times inaccurately reported that there were no side effects reported in the studies. This was not the case; there were no serious adverse events, but there were side effects. The most common side effects reported were irritation of the mouth and throat.
The Guardian (among other sources) printed some interesting reactions to the study.
Professor Robert West, editor-in-chief of the journal Addiction, was quoted as saying: “It’s early days, but it seems that these devices are already helping tens of thousands of smokers to stop each year.”
Dr John Middleton, the vice-president of the UK Faculty of Public Health, took a more cautious view and said: “It’s taken decades of sustained effort to create a society in the UK where smoking is now not seen as the norm. Our concern is that e-cigarettes could reverse this and create a new generation of customers for the tobacco industry, who might otherwise not have started smoking.”
What kind of research was this?
This was a systematic review and meta-analysis that aimed to assess how effective e-cigarettes are in helping people to stop smoking in the long term. The review also looked at whether e-cigarettes help to reduce the number of cigarettes smoked and if they are associated with any adverse events.
As this was a systematic review of all randomised controlled trials (RCTs), cohort studies and crossover trials (published and unpublished), this brings together the best available evidence on the subject.
What did the research involve?
The researchers searched all relevant medical databases for trials of at least six months' duration that compared e-cigarettes with a control condition. The RCTs, cohort studies and crossover trials were sorted using strict inclusion criteria, and from this they were able to estimate the effect of e-cigarettes.
The following databases were searched from 2004 to July 2014: the Cochrane Tobacco Addiction Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, PsycINFO and CINAHL.
In total, 21 studies were included in the review. Just two of them were RCTs and nine were ongoing studies that have not yet been completed.
One RCT was the ASCEND trial, in which 657 smokers in New Zealand were randomly assigned to have one of the following for 12 weeks after they chose to stop smoking:
- e-cigarette with 16mg nicotine
- nicotine patches with 21mg/24-hour nicotine
- e-cigarette with no nicotine (placebo e-cigarette)
Their smoking status was assessed six months after the start of the trial (their target stop smoking date) using expired carbon monoxide readings. If they were still smoking, they were asked to report the amount of daily cigarette use.
In the other RCT, the ECLAT trial, 300 smokers in Italy who were not intending to quit smoking in the coming 30 days were randomly assigned to have access to one of the following for up to four times a day:
- e-cigarette with 7.2mg nicotine
- e-cigarette with 7.2mg nicotine for six weeks and then 5.2mg nicotine for six weeks
- e-cigarette with no nicotine
They were followed up regularly over the next 12 months.
The 19 other studies were considered to be at high risk of bias and did not directly compare e-cigarettes with something else, so are not described in detail here.
What were the basic results?
In the ASCEND trial, there was no significant difference between the three groups. In the ECLAT trial, there was no significant difference between the two groups using e-cigarettes with nicotine and the group without nicotine.
Pooling the results of both RCTs:
- using an e-cigarette with nicotine increased the chances of stopping smoking for at least six months (9% of participants) compared to using a placebo e-cigarette (4% of participants), (relative risk (RR) 2.29, 95% confidence interval (CI) 1.05 to 4.96)
- a higher number of people were able to reduce cigarette consumption by at least half using e-cigarettes with nicotine (36% of participants) compared with placebo e-cigarettes (27% of participants) (RR 1.31, 95% CI 1.02 to 1.68)
- a higher number of people were able to reduce cigarette consumption by at least half by using e-cigarettes with nicotine (61% of participants) compared with a nicotine patch (44% of participants) (RR 1.41, 95% CI 1.20 to 1.67)
There were no serious adverse events associated with e-cigarettes. The most common side effect was irritation of the throat and mouth.
How did the researchers interpret the results?
The researchers conclude that “there is evidence from two trials that ECs [e-cigarettes] help smokers to stop smoking long term compared with placebo ECs. However, the small number of trials, low event rates and wide confidence intervals around the estimates mean that our confidence in the result is rated ‘low’”. They go on to say that “ECs appear to help smokers unable to stop smoking altogether to reduce their cigarette consumption when compared with placebo ECs and nicotine patches”, but they also felt the evidence for this was of a low standard.
This comprehensive systematic review and meta-analysis has found some evidence that e-cigarettes with nicotine may help people to stop smoking, or at least reduce the amount they are smoking by over half.
That said, no matter how rigorously they are carried out, systematic reviews and meta-analyses can only be as good as the size and quality of evidence that go into them. In this case, the evidence was slim.
The improvements were only apparent when the results of both RCTs were pooled together. There was no statistically significant result in either study on their own, despite having 657 and 300 participants respectively. This was mostly due to the low number of people who were able to stop smoking for at least six months in each study.
The researchers themselves are quick to point out that their confidence in the results is low because of this and the fact that they were only able to identify two relevant RCTs. (Cochrane researchers have a reputation for erring on the side of caution; their unofficial motto is “more research is needed on the topic”.)
The other types of studies identified did not directly compare e-cigarettes with another smoking cessation aid or no intervention, so they could not be included in the pooled meta-analysis.
Though the results show only a small benefit, it should be noted that in the first trial only a third of the participants accessed telephone support during their attempt to quit smoking, and increased support may have improved their success rates. In the second trial, none of the participants wanted to stop smoking in the first place, which is likely to have had a high impact on the number who quit.
Lastly, the studies did not report any serious adverse effects from the use of e-cigarettes, though mouth and throat irritation were commonly reported. As the studies were only of six months and just over a year's duration respectively, this research does not show what the long-term impact of e-cigarettes may be. Nicotine can increase the heart rate, and cause headaches and heartburn, to name just a few symptoms.
A combination of methods may be more effective for people who are keen to stop; using e-cigarettes to cope with the initial nicotine cravings and then weaning yourself of your addiction using gradually lower-dose patches or gum could be one way.
If you are determined to quit, it may be a good idea to make an appointment with an NHS stop smoking adviser. NHS stop smoking advisers are free, friendly and flexible, and can massively boost your chances of quitting for good.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.