Two new studies looking at whether electronic cigarettes help smokers to quit their deadly habit have found that while some of them can, it depends on the type and how often it is used.
The research -- welcomed by experts in a field marked by a dearth of good scientific evidence and intense lobbying -- suggests daily use of so-called "tank" e-cigarettes, designed to be refilled with nicotine-containing liquids, is most likely to help smokers quit.
Many experts think e-cigarettes, which heat nicotine-laced liquid into an inhalable vapor, are a lower-risk alternative to smoking, but questions remain about their use and safety.
The charity Action on Smoking and Health says more than 2 million adults in Britain use e-cigarettes. So-called "cigalike" e-cigarettes are disposable or use replaceable cartridges, while "tank" models look quite different and have refillable containers of nicotine "e-liquid".
Researchers who conducted the two new studies, published in the journal Addiction and Nicotine & Tobacco, said they show that smokers wanting to use e-cigarettes to quit should use them daily and try "tanks" rather than "cigalikes".
"Our research indicates that daily use of tank models that can be refilled with liquid may give smokers a better chance of quitting smoking," Ann McNeill, a professor at the Institute of Psychiatry, Psychology & Neuroscience at King's College London who was involved in both studies, told reporters.
The two studies were based on a survey of around 1,500 smokers in Britain in December 2012, followed up one year later.
The first found 65 percent of daily e-cigarette users in December 2012 tried to quit smoking in the next year compared with 44 percent of non-users. Some 14 percent of daily e-cigarette users had cut their consumption of tobacco cigarettes by at least 50 percent over the previous year, compared with only six percent of non-users.
In the second study, researchers found that of 587 people using e-cigarettes at the one year follow-up, 76 percent used "cigalikes" and 24 percent used "tank" models. Almost a third of daily tank users had quit smoking, compared with 13 percent of smokers not using e-cigarettes.
"At this point we don't know why people who use tank type e-cigarettes daily are more likely to have quit," said Sara Hitchman, who led the second study.
"Research suggests that tanks might deliver nicotine more effectively and perhaps be more satisfying ... but there may also be other factors, including price and the ways that tanks allow the user to adapt the product."
(Reporting by Kate Kelland; Editing by Janet Lawrence)