Lifestyle and exercise

Study doesn't prove e-cigs make quitting smoking harder

"E-cigs don’t help smokers quit fags – in fact they make it harder to stop," the Daily Mirror reports, apparently turning on its head the common view that using e-cigarettes can help you quit smoking conventional cigarettes.

The Mirror’s report – echoed in the Daily Mail – was based on surveys of American smokers’ habits and intentions to quit. The study found that people who had ever used e-cigarettes were about half as likely to have reduced their smoking or quit one year later compared to those who said they would never use them.

This might look like a significant finding considering the controversy over whether e-cigarettes are a useful aid to quitting. But we don’t know whether the people who used e-cigarettes were actually using them to try and quit, or whether they actually used them between the first and second surveys. There may be many factors including lifestyle and use of other smoking cessation therapies, which were not considered by the researchers.

Ideally, a well-conducted randomised controlled trial would be needed to examine the effect of e-cigarette use on the success of people wanting to quit, comparing success rates between e-cigarette users and those using other smoking cessation methods.

The studies – and debate – into the pros and cons will continue, but this study does not prove that e-cigarettes make it harder to stop.

Where did the story come from?

The study was carried out by researchers from the University of California and San Diego State University. The California Department of Public Health supported data collection for the California Smokers Cohort but no other further sources of financial support are reported.

The study was published in the peer-reviewed medical journal, the American Journal of Public Health.

The media coverage takes these study findings as conclusive and does not consider the important limitations of this study. For one thing, saying that e-cigarettes "make quitting smoking harder" is not demonstrated by this study. That’s because we don’t know whether the people who reported ever using e-cigarettes were using them as a way of trying to quit in the first place. Also, the researchers don’t report whether or how often this group of people used e-cigarettes in the year between surveys.

What kind of research was this?

This was a longitudinal study of Californian smokers who were surveyed twice (12 months apart). The researchers wanted to see if people who had ever used electronic cigarettes were more likely to quit than those who had never used e-cigarettes.

Using e-cigarettes, or "vaping", is a hotly debated area. E-cigarettes and associated products are a relatively new phenomenon and they have not been extensively studied. Currently, it is unclear whether they are of any benefit for quitting smoking, or whether they may even be harmful to society in introducing a new form of nicotine addiction.

This type of study cannot answer the question for us. It can only look at associations between reported e-cigarette use at one point in time and quitting later. It cannot tell us whether e-cigarette use is directly causing the quitting (or lack of quitting) or what other factors may be involved. High-quality randomised controlled trials would be needed for that.

What did the research involve?

This study used the California Smokers Cohort (CSC), a longitudinal survey designed to investigate factors that predict "cigarette cessation behaviour" in current and former smokers in California.

The researchers carried out a baseline telephone survey of Californian residents and identified 1,000 people aged 18-59 years who were current smokers. These people were re-interviewed using the same survey one year later.

Current smokers were defined as those who had smoked at least 100 cigarettes in their lifetime, and were smoking on at least some days at the time of the survey. Frequency of smoking was recorded only as daily or non-daily (on some days). Smokers were questioned about nicotine dependence by deeming those who needed a cigarette within 30 minutes of waking up as a sign of greater addiction.

The smokers were asked about their intention to quit, with options being:

  • never expect to quit
  • might quit in the future but not in the next six months
  • will quit in the next six months
  • will quit in the next month

The first two groups were combined as "no current intention to quit", the last two as "intending to quit in the next six months".

The smokers were also asked if they had heard of e-cigarettes, and if they had they were asked "what describes you best regarding your use of e-cigarettes: you have used e-cigarettes, you might use e-cigarettes, or you will never use e-cigarettes?"

The outcomes the researchers were interested in were:

  • whether smokers had achieved a self-reported 20% reduction in the number of cigarettes smoked each month
  • any self-reported quit attempts in the past year
  • current abstinence from cigarette use (those reporting abstinence of one month or longer)

The researchers took into account potential confounding factors of intention to quit, level of addiction, age, gender, ethnicity and years of education.

What were the basic results?

In the first survey, around a quarter of people had used e-cigarettes, and roughly a third each said they might use them, or would never use them. The remainder had never heard of them.

Sixty per cent of the sample had greater addiction in terms of needing a cigarette within 30 minutes of waking, and just over half of the sample (57%) said they had no intention of quitting smoking in the next six months.

At follow-up, 41% had made a quit attempt in the past year, a third had reduced their consumption, and 9% had achieved abstinence, quitting smoking completely.

People who said they had ever used e-cigarettes were about half as likely to have reduced monthly consumption one year later compared to those who said they would never use them (odds ratio [OR] 0.51, 95% confidence interval [CI] 0.30 to 0.87).

Factors significantly associated with increased likelihood of reduced smoking were younger age (18-44 versus 45-59 years), being a daily smoker (rather than an occasional smoker), and reported intention to quit in the next six months.

People who had ever used e-cigarettes were also less likely to be abstinent at 12 months compared to those who said they would never use them (OR 0.41, 95% CI 0.18 to 0.93).

Intention to quit was associated with a significantly increased likelihood of quitting smoking, and people who were daily smokers were significantly less likely to quit than occasional smokers.

How did the researchers interpret the results?

The researchers conclude that: "Smokers who have used e-cigarettes may be at increased risk for not being able to quit smoking. These findings, which need to be confirmed by longer-term cohort studies, have important policy and regulation implications regarding the use of e-cigarettes among smokers."


This study found that people who have used e-cigarettes may be less likely to quit smoking, but it can’t prove that’s the case. There are limitations to the findings and confirmation is needed from other studies.

The two surveys can only look at factors associated with quitting, but we can’t be certain that the e-cigarette use had any direct influence upon this. There are likely to be many unmeasured factors that could be influencing the results, including lifestyle factors and use of other smoking cessation therapies. We also don’t know whether the smokers actually used e-cigarettes as a quitting aid during the year between the first and second surveys.

The researchers did assess people’s intentions to quit smoking in the first survey, and adjusted for this in their analyses. However, it may be difficult to fully capture people’s intentions, and these may have changed. It may be that the people who used e-cigarettes were not doing so to quit or were less serious about quitting, while those who were, chose to use other smoking cessation therapies.

Ideally, high-quality randomised controlled trials looking particularly at people who want to quit and whether they use e-cigarettes or other smoking cessation methods are needed. These trials would also need to carefully follow people at intervals and take scientifically validated, in-depth assessments of their smoking status, rather than just relying on people’s self-reported smoking status in a telephone survey, which may not give reliable results.

Other limitations to this study include that the sample of Californian residents may be unrepresentative of other populations worldwide.

The use of e-cigarettes, including whether they actually help people to quit, or whether they may have harmful effects, such as introducing a new form of addiction, will continue to be studied and debated.

Read more about treatment and support to quit smoking.  

NHS Attribution