Using e-cigarettes frequently does help smokers break the habit, according to a US study involving more than 24,500 people who currently smoke or have recently quit.
It is the largest sample of smokers studied to date and the researchers say the findings help to unpick some of the mixed messages about whether or not e-cigarettes have benefit in quit attempts.
But the Royal Pharmaceutical Society (RPS) has said it remains concerned about the evidence base for the efficacy and long-term safety of e-cigarettes.
The study, carried out by a team from Georgetown Lombardi Comprehensive Cancer Center in Washington DC, used data from the 2014–2015 Tobacco Use Supplement-Current Population Survey — a survey done every three to four years across the country using phone or in-person interviews — and found that the key to success seemed to be how often smokers were using e-cigarettes when trying to quit.
Analysis showed a linear correlation between quit attempts and quit success and the frequency of e-cigarette use
Attempting to quit in the first place was more likely among smokers using e-cigarettes than non-users, the researchers found.
And among smokers making at least one quit attempt, success was higher among those with at least five days use of e-cigarettes in the last month.
However, the data also showed that among those making at least one quit attempt, success was lower among individuals who had used e-cigarettes at some point in the past.
Alex MacKinnon, director for Scotland at the RPS, said: “The RPS remains concerned about the evidence-base for the efficacy and long-term safety of e-cigarette use. We acknowledge that, once we have MHRA regulated and approved products on the market, there may be a role for e-cigarettes as a potential part of smoking cessation programmes.
“This study’s findings must be considered within the context of other emerging research and evidence. The RPS is currently reviewing its position and policy from 2014, taking into account new evidence to ensure our views are based on available evidence, to support our members who deliver smoking cessation services.”
Study lead, David Levy, professor of oncology at Georgetown Lombardi, said the data showed important nuances in terms of how successful a person might be in stopping smoking.
“Both cigarette quit attempts and quit success were directly related to the number of days of e-cigarette use,” he said.
“The odds of quit success increased by 10% with each additional day of e-cigarette use.”
He added: “Our findings are consistent with randomised trials and those observational studies that measure frequency of e-cigarette use.
“These results support the use of e-cigarettes — especially, consistent use — as an effective smoking cessation aid.
“Since e-cigarettes are generally estimated to have a small proportion of the mortality risks of cigarettes, this represents an important life-saving intervention that doctors can recommend when other forms of treatment fail.”
 Levy D, Yuan Z, Luo Y et al. The relationship of e-cigarette use to cigarette quit attempts and cessation: insights from a large, nationally representative US survey. Nicotine Tob Res 2017;1–9. doi: 10.1093/ntr/ntx166