Smoking kills. That such a damaging and irrational behaviour persists in many countries where the health risks of smoking are well understood and most smokers want to quit, is testimony to the power of nicotine addiction. Quitting is difficult, particularly without medication and behavioural support, but persuading smokers to accept help can also be difficult: most choose to quit unaided, and usually fail.  Regular smokers therefore tend to remain smokers for decades, and in due course half are killed by their smoking. The numbers involved are huge: the UK alone has 7 million smokers and hence up to 3.5 million preventable early deaths among today’s smoking population, while the global total of 1 billion smokers,  indicates that one in fourteen people on the planet today may die from tobacco. This persistence of smoking after decades of awareness that smoking is a mass killer is prime facie evidence of a systematic failure of public health.
The effects of nicotine on the human body are broadly similar to those of caffeine, indicating that long term use probably represents a health risk similar to that of coffee consumption. Since the harms of smoking arise not from nicotine, but from the many other toxins in tobacco smoke, it follows that providing smokers with nicotine in a smoke free formulation should enable smokers to quit smoking more easily, by removing the need to overcome addiction to nicotine. Unlike conventional nicotine replacement therapies, electronic cigarettes achieve exactly this by delivering nicotine in a vapour that, while not harmless, is substantially less toxic than smoke, [3-5] while also replicating the pulmonary delivery of nicotine and several other social and behavioural characteristics of smoking.
The popularity of electronic cigarettes with smokers has disrupted the markets of both the tobacco and pharmaceutical industries, demonstrating potential to transform the way that nicotine is used in society and, as a result, prevent millions of deaths. Their emergence has also wrong footed medical authorities such as the World Health Organisation which, with others, has chosen to cite the precautionary principle as a reason to restrict or prohibit their use on the basis of uncertainty over short and long term health harms, risk of gateway progression to smoking in young people, perpetuation of smoking through dual use, and exploitation by the tobacco industry to undermine tobacco control policies. [6-8] A recent cluster of cases of serious lung disease in the USA, including several deaths,  seemingly linked to the use of electronic cigarettes to consume cannabinoids,  has led the American Medical Association to recommend against all electronic cigarette use.  Are these precautionary responses justified?
The UK has taken a global lead in seeking to capitalise on the potential benefits of electronic cigarettes, with public health and medical authorities encouraging their use by smokers, [3,5] while protecting children by prohibiting most forms of advertising, outlawing sale to minors, introducing (as in all EU countries) mandatory reporting of electronic cigarette emissions, and setting upper limits on the concentration of nicotine in vaping solutions. Australia, in contrast, has prohibited electronic cigarette sale, personal possession or use, while the USA (with the recent exception of the City of San Francisco ) has taken a mixed approach by permitting advertising and the sale of high-strength nicotine products, but generally stopping short of medical endorsement as a tobacco harm reduction strategy. Recent trends in smoking among adults and children in these countries show instructive differences.
In the five years to 2017 in the UK, use of electronic cigarettes among smokers trebled,  and the prevalence of daily or occasional smoking fell rapidly, by 0.9% percentage points per year, to 15.1%.  Multiple surveys of young people across the UK demonstrate growing experimentation with electronic cigarettes but predominantly among those already using tobacco, with no evidence that this is slowing the historic sustained decline in smoking prevalence in young people. 
In the USA in the three years to 2017 the proportion of people smoking tobacco daily or on most days fell by only 0.57 percentage points per year, to 16.7%. [16,17] Data for 2019 included in a recent press release by the US Food and Drug Administration demonstrate that smoking among young people in the USA is also declining, but demonstrate rapidly growing use of electronic cigarettes,  previously linked to the emergence of Juul, a novel e-cigarette using high concentration nicotine that is reported to have been heavily promoted to young people. 
In Australia, smoking among teenagers has also continued a sustained fall,  but over the three years to 2018 the prevalence of daily and occasional smoking among adults declined by only 0.27 percentage points per year, to 15.2%. [21,22] Whilst it would be premature to attribute these differences in smoking trends solely to differences in electronic cigarette policy, the figures do suggest that the UK approach of medical endorsement with marketing controls and product regulation has to date succeeded in harnessing the potential of electronic cigarettes to significantly accelerate the decline in adult smoking prevalence while avoiding appreciable adverse effects on children.
Inhaling any foreign material is inherently likely to be harmful, and the recent US experience speaks strongly in favour of regulating electronic cigarette contents and emissions to protect users,  and regulating both the advertising and sale of electronic cigarettes to minimise use by young people and all non-smokers. However the UK experience also demonstrates that electronic cigarettes have a valuable part to play in reducing tobacco smoking and death and disability that smoking causes. Those who cite the precautionary principle as justification to discourage or prohibit electronic cigarettes ignore the fact that for the great majority of users, the counterfactual is premature death from tobacco smoking. Smoking kills. So does denying smokers opportunities to quit.
John Britton is the Director of the UK Centre for Tobacco and Alcohol Studies, University of Nottingham
Competing interests: None declared
- Tobacco Advisory Group of the Royal College of Physicians. Hiding in plain sight: Treating tobacco dependency in the NHS. Royal College of Physicians, 2018. Available from https://www.rcplondon.ac.uk/file/10116/download?token=K05kvT-7 (Accessed 31/07/2018).
- World Health Organisation. Tobacco. 2019. Available from https://www.who.int/news-room/fact-sheets/detail/tobacco (Accessed 27/06/2019).
- McNeill, A., Brose, L., Calder, R., Hitchman, S.C., McRobbie, H., and Hajek, P. E-cigarettes: an evidence update. A report commissioned by Public Health England. Public Health England, 2015. Available from https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/454516/Ecigarettes_an_evidence_update_A_report_commissioned_by_Public_Health_England.pdf (Accessed 21/03/2016).
- National Academies of Sciences Engineering and Medicine. Public Health Consequences of E-Cigarettes. 2018. Available from https://www.nap.edu/login.php?record_id=24952&page=https%3A%2F%2Fwww.nap.edu%2Fdownload%2F24952 (Accessed 03/07/2019).
- Tobacco Advisory Group of the Royal College of Physicians. Nicotine without smoke – tobacco harm reduction. Royal College of Physicians, 2016. Available from https://www.rcplondon.ac.uk/file/3563/download?token=Mu0K_ZR0 (Accessed 27/06/2017).
- World Health Organisation. Electronic Nicotine Delivery Systems and Electronic Non-Nicotine Delivery Systems (ENDS/ENNDS). WHO Framework Convention on Tobacco Control, 2016. Available from http://www.who.int/fctc/cop/cop7/FCTC_COP_7_11_EN.pdf?ua=1 (Accessed 27/06/2019).
- European Respiratory Society. ERS Position Paper onTobacco Harm Reduction. 2019. Available from https://ers.app.box.com/v/ERSTCC-Harm-Reduction-Position (Accessed 28/06/2019).
- White Paper on Electronic Nicotine Delivery System. Indian J Med Res, 2019. 10.4103/ijmr.IJMR_957_19.
- Layden, J.E., Ghinai, I., Pray, I., et al. Pulmonary Illness Related to E-Cigarette Use in Illinois and Wisconsin — Preliminary Report. New England Journal of Medicine, 2019. 10.1056/NEJMoa1911614.
- Centers for Disease Control and Prevention. Severe Pulmonary Disease Associated with Using E-Cigarette Products. 2019. Available from https://emergency.cdc.gov/han/han00421.asp (Accessed 13/09/2019).
- American Medical Association. AMA urges public to avoid e-cigarette use amid lung illness outbreak. 2019. Available from https://www.ama-assn.org/press-center/ama-statements/ama-urges-public-avoid-e-cigarette-use-amid-lung-illness-outbreak (Accessed 13/09/2019).
- BBC News. San Francisco becomes first US city to ban e-cigarettes. 2019. Available from https://www.bbc.co.uk/news/business-48752929 (Accessed 27/06/2019).
- Action on Smoking and Health. Use of e-cigarettes (vapourisers) among adults in Great Britain. 2018. Available from http://ash.org.uk/download/ash-use-of-e-cigarettes-by-adults-in-great-britain-2018-pdf/ (Accessed 14/08/2018).
- Office for National Statistics. Adult Smoking Habits in Great Britain 2017. Office for National Statistics, 2018. Available from https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/healthandlifeexpectancies/bulletins/adultsmokinghabitsingreatbritain/2017/pdf (Accessed 07/02/2018).
- Bauld, L., MacKintosh, A.M., Eastwood, B., Ford, A., Moore, G., Dockrell, M., Arnott, D., Cheeseman, H., and McNeill, A. Young People’s Use of E-Cigarettes across the United Kingdom: Findings from Five Surveys 2015-2017. Int J Environ Res Public Health, 2017; 14.
- Wang, T.W., Asman, K., Gentzke, A.S., Cullen, K.A., Holder-Hayes, E., Reyes-Guzman, C., Jamal, A., Neff, L., and King, B.A. Tobacco product use among adults—United States, 2017. 2018. Available from https://www.cdc.gov/mmwr/volumes/67/wr/mm6744a2.htm?s_cid=mm6744a2_w#F1_down (Accessed 27/06/2019).
- Hu, S.S. Tobacco product use among adults—United States, 2013–2014. 2016. Available from https://www.cdc.gov/mmwr/volumes/65/wr/mm6527a1.htm (Accessed 27/06/2019).
- US Food and Drug Administration. Trump Administration Combating Epidemic of Youth E-Cigarette Use with Plan to Clear Market of Unauthorized, Non-Tobacco-Flavored E-Cigarette Products. 2019. Available from https://www.fda.gov/news-events/press-announcements/trump-administration-combating-epidemic-youth-e-cigarette-use-plan-clear-market-unauthorized-non (Accessed 13/09/2019).
- Kamerow, D. Popular e-cigarette Juul comes under attack. BMJ, 2019; 365: l4249.
- Guerin, N. and White, V. ASSAD 2017 Statistics & Trends: Australian Secondary Students’ Use of Tobacco, Alcohol, Over-the-counter Drugs, and Illicit Substances. . Cancer Council Victoria, 2018. Available from https://beta.health.gov.au/sites/default/files/secondary-school-students-use-of-tobacco-alcohol-and-other-drugs-in-2017_0.pdf (Accessed 03/07/2019).
- Australian Bureau of Statistics. National Health Survey First Results. Australia 2014-15 2015. Available from https://www.ausstats.abs.gov.au/ausstats/subscriber.nsf/0/CDA852A349B4CEE6CA257F150009FC53/$File/national%20health%20survey%20first%20results,%202014-15.pdf (Accessed 27/06/2019).
- Australian Bureau of Statistics. National Health Survey First Results. Australia 2017-18. 2019. Available from https://www.ausstats.abs.gov.au/ausstats/subscriber.nsf/0/4B3976684C09F43FCA258399001CE630/$File/4364.0.55.001%20-%20national%20health%20survey,%20first%20results,%202017-18.pdf (Accessed 27/06/2019).