People who use electronic cigarettes do not report higher rates of quitting than regular cigarette smokers, according to a US study.
The findings were based on survey answers from 949 smokers, reported in a research letter to the Journal of the American Medical Association (JAMA) Internal Medicine.
Just over 13 per cent of the people in the study reported quitting smoking within one year.
E-cigarette use "did not significantly predict quitting one year later," said the letter, written by three researchers at the University of California, San Francisco.
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Among participants who reported using both e-cigarettes and regular cigarettes, e-cigarette use was not associated with a change in cigarette consumption, it added.
The fact that there were so few e-cigarette users in the study - just 88, and nine of whom quit - may have made any trends more difficult to spot, said the letter.
"Nonetheless, our data add to current evidence that e-cigarettes may not increase rates of smoking cessation," it said.
"Regulations should prohibit advertising claiming or suggesting that e-cigarettes are effective smoking cessation devices until claims are supported by scientific evidence."
E-cigarettes deliver nicotine through a vapour, and are currently not regulated by health authorities in the US.