Smokers who also use e-cigarettes may be half as likely to give up tobacco as smokers who never vape at all, a European study suggests.
Even when smokers only occasionally experimented with vaping, they were about 67 percent less likely to become ex-smokers, the study found. Daily e-cigarette use was associated with 48 percent lower odds of having quit regular cigarettes.
"This is important because e-cigarettes are widely promoted as a smoking cessation tool," said senior author Stanton Glantz, director of the Center for Tobacco Control Research and Education at the University of California, San Francisco.
"And, while there is no question that some smokers do successfully quit with e-cigarettes, they keep many more people smoking," Glantz said by email.
Smokers in the study also used more cigarettes a day when they vaped than when they avoided e-cigarettes altogether, researchers report in the American Journal of Public Health.
People smoked an average of about 14 cigarettes a day when they didn't vape, and around 16 cigarettes a day when they did.
Researchers analyzed data from a 2014 survey of more than 13,000 current or former smokers in the European Union. About 2,500 participants said they had tried vaping at least once.
Overall, they were 50 years old on average, 46 percent of the participants were former smokers and 19 percent currently or previously used e-cigarettes.
Among these people who had all been cigarette smokers at some point, the researchers looked at the likelihood of being an ex-smoker at the time of the survey based on whether a person used e-cigarettes.
Some past research has suggested that using e-cigarettes may help smokers cut down on use of traditional tobacco products, or even transition entirely away from tobacco.
"The findings are concerning because they suggest the idea that e-cigarettes are an even more effective cessation tool than nicotine replacement therapy - an idea aggressively marketed by e-cigarette and tobacco companies - may not be true in practice," said Samir Soneji, a health policy researcher at Dartmouth College in Hanover, New Hampshire, who wasn't involved in the study.
Most adult smokers express a desire to quit, and many try and fail, Soneji said by email. E-cigarettes might seem like an appealing cessation tool because the devices in some ways mimic the smoking, but nicotine gum or patches may be more effective.
"Most of the scientific evidence to date, including this study, finds that e-cigarette use does not lead to higher rates of smoking cessation compared to standard cessation tools," Soneji said by email.
Big U.S. tobacco companies are all developing e-cigarettes. The battery-powered gadgets feature a glowing tip and a heating element that turns liquid nicotine and flavorings into a cloud of vapor that users inhale.
The study wasn't a controlled experiment designed to prove whether or how e-cigarette use might influence the success of any smoking cessation efforts. The survey also did not ask current smokers whether they were trying to quit or cut down on tobacco use, or if they were using e-cigarettes for that purpose.
Another drawback is that researchers lacked data on when ex-smokers had quit, and it's possible some of them stopped before e-cigarettes were widely available.
A bigger question about e-cigarettes - whether they're safe or at least safer than traditional cigarettes - also isn't answered by the current study.
When e-cigarettes contain nicotine, they can be addictive like traditional cigarettes. Even without nicotine, some previous research suggests that flavorings and other ingredients in e-liquids used for vaping could be linked to serious breathing problems.
"Whether they are safer than cigarettes is almost a trick question because tobacco cigarettes are one of the most harmful substances known to medicine," said Thomas Wills, director of the Cancer Prevention in the Pacific Program at the University of Hawaii Cancer Center in Honolulu.
"It would be hard to find anything more harmful to long-term health except maybe arsenic," Wills, who wasn't involved in the study, said by email. "But this does not mean that e-cigarettes are safe."