Health officials in Britain have for the first time endorsed e-cigarettes, saying they are 95 percent safer than tobacco equivalents and even suggesting doctors should be able to prescribe the "game-changing" devices to smokers trying to quit.
E-cigarettes, which allow users to inhale nicotine-laced vapour but contain no tobacco, have surged in popularity in recent years but health bodies have so far been wary of advocating them as a safer alternative.
Governments from California to India have tried to regulate their use more strictly, many fearing they are a gateway to tobacco smoking among teenagers, and the World Health Organization has also called for curbs on the devices.
But in a study published on Wednesday, Public Health England (PHE) an agency of Britain's Department of Health, backed their use.
"E-cigarettes are not completely risk-free but when compared to smoking, evidence shows they carry just a fraction of the harm," said PHE's Professor Kevin Fenton in a statement.
The study said that since most of the chemicals that cause smoking-related diseases are absent in e-cigarettes, with the current best estimate that e-cigarette use is around 95 percent less harmful to health than smoking, governments should offer them to people looking to quit.
While e-cigarettes do contain nicotine, an addictive drug, it is not nicotine that kills smokers but rather chemicals in the tar found in the smoke.
Although British doctors and stop-smoking services cannot currently prescribe e-cigarettes as none of the products on the market is licensed for medicinal purposes, the report's authors hope that hurdle will be removed.
"Given the potential benefits as quitting aids, PHE looks forward to the arrival on the market of a choice of medicinally regulated products that can be made available to smokers by the NHS on prescription," the report said.
Read: Anti-tobacco advocate says electronic cigarettes are potential life-savers
Contradicts with what the WHO says
The publicly funded study goes against a 2014 report by the World Health Organization that called for stiff regulation of e-cigarettes and bans on their indoor use and sale to minors.
It also contradicts the findings of researchers from the University of Southern California who said this week that U.S. teens who tried electronic cigarettes might be more than twice as likely to move on to smoking conventional cigarettes as those who have never tried the devices.
The British study said e-cigarettes, which are already the most popular quitting aids in Britain and the United States, could be a cheap way to reduce smoking in deprived areas, which still have a high proportion of smokers.
"E-cigarettes could be a game-changer in public health in particular by reducing the enormous health inequalities caused by smoking," said Professor Ann McNeil, who helped author the study.
The study criticised media campaigns that have called e-cigarettes equally or even more harmful than smoking that could serve as a gateway to tobacco cigarettes among teenagers.
"There is no evidence that e-cigarettes are undermining England's falling smoking rates," McNeil said.
"Instead the evidence consistently finds that e-cigarettes are another tool for stopping smoking and in my view smokers should try vaping, and vapers should stop smoking entirely," she added.
Almost all of the 2.6 million adults using e-cigarettes in Britain are current or ex-smokers who are using the devices to help them quit and only 2 percent of young people are regular users, the study said.
Read: How South African's quit smoking
The study is welcomed by campaigners
Public health charities welcomed the study's attempt to clear up the facts behind e-cigarettes.
"There are still nearly 8 million smokers in England, many of whom would benefit from switching to electronic cigarettes, but who may have been put off doing so because of unfounded health concerns," the British charity Action on Smoking and Health said in a statement.
"If every smoker switched overnight to electronic cigarettes many hundreds of thousands of premature deaths would be prevented in the years to come,” it said.
The global tobacco industry sells about 5.7 trillion cigarettes a year, but is seeing that number shrink due to increased health consciousness, weak consumer spending and higher taxes, as well as competition from cheap black-market packs and e-cigarettes.
The four international big tobacco firms – Philip Morris International, British American Tobacc, Imperial Tobacco Group and Japan Tobacco - have all invested in e-cigarettes as a way to diversify revenue.
Imperial Tobacco has applied to UK health regulators for its Puritane e-cigarette to be licensed as a medical device, which would allow it to make claims related to health or smoking cessation. BAT's Voke, an inhaler but not an e-cigarette, already has approval.
Calling the study an "incredibly important milestone", a BAT spokesman acknowledged the risk posed by chemicals found in cigarette smoke and said increasing sales of e-cigarettes would greatly benefit their customers' health.
E-cigarette sales, concentrated in markets such as Britain, France and the United States, are growing but exact figures are difficult to track, because many purchases occur online or in independent "vape shops".
Wells Fargo analyst Bonnie Herzog thinks they will outsell cigarettes over the next decade.
Another analyst, Phil Gorham at Morningstar, said he expected the British PHE's endorsement of e-cigarettes to give a further boost to their popularity and that the industry could be close to a tipping point as it turns away from its traditional tobacco market.
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