Electronic cigarettes (e-cigarettes) appear to help smokers abstain from cigarette smoking and reduce smoking levels in persistent smokers, but more evidence is required before definitive recommendations can be made about their efficacy as a smoking cessation tool.
A Cochrane Review showed that e-cigarettes double the likelihood of quitting smoking compared with placebo and that they increase the likelihood of reducing smoking levels by more than 30%.
However, the investigators caution that there are few studies on the effectiveness of e-cigarettes and that the quality of the available evidence is low.
"The important thing, to put it into context, is that we looked at them as a smoking cessation treatment, and there are established smoking cessation treatments with a lot more evidence out there that have been around for longer and have evidence to back them up," review coauthor Jamie Hartmann-Boyce, a doctoral candidate and research associate at the Cochrane Tobacco Addiction Group, part of the Nuffield Department of Primary Care Health Sciences, at the University of Oxford, United Kingdom, told Medscape Medical News. "Basically, this is the first step."
The study was published online 17 December in the Cochrane Database of Systematic Reviews.
More Evidence Needed
To determine the efficacy of e-cigarettes to help smokers achieve abstinence for at least 6 months or reduce cigarette consumption by at least 50%, the researchers searched the Cochrane Tobacco Addiction Groups Trials Register, the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, and two other databases for relevant studies published between 2004 and 2014.
Of 600 records initially identified, 13 complete studies met the inclusion criteria, comprising two randomized controlled trials (RCTs) and 11 cohort studies. The RCTs compared e-cigarettes with placebo (nonnicotine) e-cigarettes in a combined sample of 662 individuals.
Analysis revealed that people using active e-cigarettes were more likely to abstain from smoking for at least 6 months compared with those using placebo e-cigarettes, at 9% vs 4% (risk ratio [RR], 2.29). However, the quality of the evidence was deemed to be low.
It was also shown that more people were able to reduce cigarette consumption by at least half with active e-cigarettes vs placebo, at 36% vs 27% (RR, 1.31). Again, the quality of the evidence was low.
Compared with a nicotine patch, e-cigarettes did not have a significant impact on 6-month abstinence rates (RR, 1.26), although the researchers note that the difference could be clinically meaningful.
More people were able to reduce cigarette consumption by at least half with e-cigarettes compared with patches, at 61% vs 44% (RR, 1.41). However, in both comparisons with nicotine patches, the evidence was judged to be of very low quality.
"From our perspective, the bottom line for us is that it shows promise, but we really want to see more studies."
"For example, if you compared the evidence we have on e-cigarettes to the evidence we have on more traditional forms of nicotine replacement therapies, like patches or gum, our Cochrane Review of that has 100 studies with over 50,000 participants."
A Case of Wait and See
She added that more evidence is therefore required on e-cigarettes. To that end, nine ongoing studies are due to report in the next couple of years.
Although they will hopefully offer a clearer picture of the effectiveness of e-cigarettes, the impact the results will have on the conclusions of the Cochrane Review is unknown.
"I think it's a case of wait and see," said Hartmann-Boyce.
"The reason why we do these reviews is that we know that different studies will throw up slightly different answers. That could just be because of chance, but it also could be because they are going to be in different populations and also using different types of e-cigarettes," she added.
She also stressed that the two studies included in the current analysis used first-generation technologies, adding: "The technology used in later trials might be slightly better at delivering nicotine."
"We don't know that, but I wouldn't be able to say either way if I predict they will be saying the same thing [as the current studies]. If they did say a similar thing, they would certainly increase our confidence in the findings."
It is not unusual for treatments of this kind to become widely available without a large body of evidence. Although the current review found no serious adverse events plausibly related to e- cigarettes, concerns have been raised about whether they are safe, given the lack of supporting data.
"A lot of the concerns about the health risks that might be posed by e-cigarettes come from a more public health perspective," said Hartmann-Boyce.
"In our review, what we were looking at were people who were already regularly smoking traditional cigarettes, which is something that we already know poses a risk," she noted.
She observed that the broader concerns and controversy around e-cigarettes stem from people using them who might not be traditional smokers. However, that did not form part of the review.
One notable aspect of the findings was that the overall quit rate was low, at less than 10%, even with active treatment. This is partly due to the definition of cessation used in the study. "We were not looking at people who have just quit for a couple of weeks," Hartmann-Boyce said.
"We want them to quit for at least 6 months and, in these cases, have that biochemically validated as well."
Consequently, the investigators were not surprised to see the low quit rates. Nevertheless, Hartmann-Boyce does not believe that newer, better cessation treatments are required to achieve higher quit rates.
"We know that it is really hard to quit smoking in the long term. Obviously if there was a great new treatment that sorted out the problem, fantastic, but it doesn't signal the complexity of the problem," she said.
"What we do know is that a lot of people try quitting, don't succeed, try again, don't succeed, and then try again and then might succeed. That is something that people often have to try a few times and a few different methods before they figure out the one that works for them."
Jamie Hartmann-Boyce has disclosed no relevant financial relationships.
Cochrane Database Syst Rev. Published online December 17, 2014. Abstract
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Cite this: e-Cigarettes for Smoking Cessation: Jury Still Out - Medscape - Dec 17, 2014.