18B.6Potential negative impacts

Last updated: May 2020
Suggested citation:
Greenhalgh, EM, & Scollo, MM. InDepth 18B: Electronic cigarettes (e-cigarettes). In Scollo, MM and Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2020. Available from:  http://www.tobaccoinaustralia.org.au/chapter-18-harm-reduction/indepth-18b-e-cigarettes

 

At the heart of the debate over the utility of e-cigarettes is concern about the extent to which the potential benefits of making a likely-less harmful alternative to tobacco widely available to smokers might be outweighed by several potential risks. Risks identified to date include uptake by non-smokers, gateway effects, dangers associated with dual use, discouragement from smoking cessation, renormalising smoking, and allowing the tobacco industry to influence decision-making in public health.1-3

18B.6.1 Uptake among non-smokers

Experimentation with e-cigarettes among non-smoking middle-aged to older adults appears to be relatively rare.4, 5 Among young people however, use is increasing, in some countries quite rapidly (see Section 18B.3). While initial reports indicated that e-cigarette use occurred predominantly among adolescents who had also experimented with tobacco,6 more recent data shows increasing use among never smokers.7 An analysis of trends from 2011 to 2015 in e-cigarette use among US adolescents found that over time, past month e-cigarette users increasingly encompassed those who were not users of other tobacco products.8  During 2017–2018, current e-cigarette use among US high school students increased by 78% (from 11.7% to 20.8%),9 leading the US FDA to label e-cigarette use among youth an ‘epidemic’.10 In 2019, 27.5% of US high school students and 10.5% of middle school students reported current use of e-cigarettes.11 Among adults, one study reported that in 2016 in the US, 1.4% of never smokers reported using e-cigarettes, and of these users, about 60% were aged 18 to 24.12 Another US study found that the prevalence of current e-cigarette use increased significantly among adult never smokers between 2015 and 2018.13 An Australian study found that curiosity and one’s social environment were strongly associated with intentions to use e-cigarettes among young adult non-smokers.14

Use of e-cigarettes by children and non-smokers—either as a step toward smoking (see Section 18B.6.2, below) or exclusively—is a concern to public health specialists and regulators. Research in Europe found that while most university students who smoke report some desire to quit, those who use e-cigarettes do not report the same desire.15 Exposure to nicotine during adolescence may have significant and lasting health consequences,16 including long-term addiction to e-cigarette delivered nicotine.17 One of the most popular e-cigarette brands in the US among adolescents, JUUL, exposes users to high levels of nicotine;18 however several studies have shown that most young people are unaware of JUUL’s high nicotine concentration.19, 20 Further, although many researchers have concluded that the adverse health effects of e-cigarette use are likely less than those of cigarettes, the long-term consequences are still not well understood. Limited evidence suggests that e-cigarette use—particularly when e-liquids include sweet flavourings21, 22—may increase users’ risks of cardiovascular and respiratory disease (see Section 18B.5). Some adolescents are also using e-cigarettes for vaping of cannabis and other substances which pose additional risks (see Section 18B.4).23

As with tobacco cigarettes, exposure to e-cigarette marketing and promotion is associated with greater e-cigarette use among young people.24-27 (see Section 18B.2.3). Along with curiosity, the wide range of fruit, candy, and other sweet flavours is one of the most commonly cited reasons for experimentation among children.28-31 The presence of flavouring and/or nicotine at the first e-cigarette exposure is associated with progression to current and more frequent e-cigarette use among adolescents,32-34 and can also decrease perceptions of harm.35 Non-tobacco flavours may be particularly appealing to never smokers when compared with smokers.36 Although such flavours have largely been banned in conventional cigarettes in Australia37-42 and the US43 mostly due to their appeal to children, and despite the high levels of toxic compounds found in flavoured e-cigarettes,44, 45 it has been estimated that there are over 7500 different flavours of e-liquid available.46

A 2019 investigation into JUUL Labs Inc.’s role in the ‘youth nicotine addiction epidemic’ in the US determined that JUUL Labs Inc. had deliberately targeted children in order to become America’s largest seller of e-cigarettes. Specifically, a Subcommittee found: JUUL deployed a sophisticated program to enter schools and convey its messaging directly to teenage children; JUUL targeted teenagers and children, as young as eight years old, in summer camps and public out-of-school programs; and JUUL recruited thousands of online ‘influencers’ to market to teens.47, 48

Together, these issues have led to calls for strict regulations that would minimise use among young people and non-smokers, including restrictions on advertising and promotion, prohibiting use in smokefree areas, banning flavours that could appeal to youth, raising taxes, implementing health warnings, and prohibiting sales to minors.49, 50 In 2018, the FDA launched a public education campaign to educate teenagers about the risks of e-cigarettes, and proposed having flavoured e-cigarettes (other than tobacco, mint and menthol flavours) only sold in age-restricted, in-person locations and, if sold online, under heightened practices for age verification.10, 51 The FDA has also conducted large-scale undercover checks of retailers, resulting a significant number of warning letters for violations related to the for illegal sales of JUUL products to youth.52 Programs and policies have also been developed and implemented in some US high schools, aiming to prevent e-cigarette use among young people.53, 54

18B.6.2 A ‘gateway effect’ to tobacco smoking

Of great concern to public health experts is the growing body of research suggesting a possible relationship between e-cigarette use and the uptake and escalation of smoking among young people.  A 2016 meta-analysis concluded that never-smoking adolescents and young adults who use e-cigarettes are more likely to intend to smoke,55 and a systematic review in the same year concluded that e-cigarette use is associated with an increase in smoking, even among adolescents not susceptible to smoking.56 A major review published in 2018 concluded that there is substantial evidence that e-cigarette use increases risk of ever using combustible tobacco cigarettes among youth and young adults,57 and another concluded that the evidence for a strong positive relationship between use of e-cigarettes and later cigarette smoking among youth continues to accumulate.58 A 2019 meta-analysis found that e-cigarette use by adolescents is associated with a 2- to 4-fold increase in cigarette smoking over the next year.59 Compared with older teenagers, onset of e-cigarette use at a younger age appears to be associated with increased odds of smoking.60 Australian researchers found that, among young adults who had never smoked, curiosity, willingness and intentions to smoke tobacco cigarettes were higher among young e-cigarette users than never users.61 Several studies have suggested that the relationship may be bi-directional, such that smoking increases the risk of e-cigarette use, and e-cigarette use increases the risk of smoking.62-64 Use of e-cigarettes among youth and young adults may increase consumption of conventional cigarettes and duration of smoking.57 E-cigarette susceptibility and use may also predict marijuana and alcohol use over time.65-67

Studies such as those described above cannot establish causation (i.e., e-cigarette use could be a marker in young people who would have gone on to use conventional cigarettes regardless; one cannot rule out the possibility that the relationship between e-cigarette use and smoking is explained by another/other variable/s68). However several studies have noted conventional cigarette uptake among e-cigarette users who would be considered least at risk of smoking,56, 69-73 and the best-quality studies and reviews have attempted to control for underlying susceptibility. Several possible mechanisms of how e-cigarette use may act as a ‘gateway’ to smoking have been proposed. E-cigarette use could normalise nicotine use and smoking behaviours more generally, leading to the renormalisation of smoking, or it could cause users to develop nicotine addiction.55, 69 The use of e-cigarettes with higher concentrations of nicotine has a stronger association to later cigarette use.58, 74

Alternatively, some have suggested that, rather than acting as a ‘gateway’, e-cigarettes may be acting as a ‘diversion’ among young people. That is, e-cigarette use partially or wholly replaces cigarette smoking, and may therefore accelerate the decline in youth cigarette smoking.75 They note that increases in use of non-cigarette tobacco/nicotine products has increased substantially in the US75 and UK,76 alongside a decline in cigarette smoking. One study examining US survey data concluded that a long-term decline in smoking prevalence among US youth and young adults accelerated after 2013 when e-cigarette use became more widespread, which the authors argue demonstrates that e-cigarettes have had a negligible effect on youth smoking at the population level and may support the diversion theory.77 However, critics of this theory argue that continued declines in smoking might alternatively be attributed to the continuing and long-term effects of current and historical comprehensive tobacco control programs.78, 79

18B.6.3 Prolonged dual use

Dual use refers to the concurrent use of conventional tobacco products and e-cigarettes.  Dual use is actively promoted by some e-cigarette manufacturers, especially those that also manufacture tobacco products, as a way for smokers to by-pass smokefree regulations,46 and this is a commonly cited reason for e-cigarette use among smokers.80, 81 Other smokers use both products as a means of cutting down the number of cigarettes they smoke each day, and/or as an intended pathway to complete smoking cessation.82, 83 However, many smokers are unsuccessful in transitioning fully from smoking to vaping, despite initial intentions to quit smoking.80 One study in England found that long-term use of e-cigarettes was similarly prevalent among current and recent ex-smokers, indicating continued dual use was a common pattern, although this was not associated with reduced motivation to quit.84 Research in the US similarly found continued high prevalence of dual use among adults between 2015 and 2018.13 Another English study found that dual users of e-cigarettes had lower quit attempt rates than dual users of NRT.85

While a reduction in risk seems likely for smokers who completely substitute tobacco cigarettes,86, 87 the benefits for those who continue to use some tobacco cigarettes are much less certain. Among those who exclusively smoke tobacco cigarettes, cutting down the number of cigarettes consumed may not reduce toxic exposure if smokers compensate by drawing more deeply on the cigarettes they do smoke. There is some evidence that supplementing reduced cigarette consumption with an alternative source of nicotine might reduce toxicant exposure and hence mortality among smokers who continue to smoke at a reduced rate—see section 18B.7.388-90  However, there is no available evidence whether or not long-term e-cigarette use among smokers changes morbidity or mortality compared with those who only smoke tobacco cigarettes.57 Use of e-cigarettes has the potential to introduce independent or additive health risks.58, 91

18B.6.4 Discouragement from cessation

Smokers taking up e-cigarettes while still smoking tobacco cigarettes, who might otherwise have quit altogether had they not commenced e-cigarette use, might represent missed opportunities for complete cessation. So far, although many current and former smokers state a preference for e-cigarettes as a cessation aid, evidence for the effectiveness of e-cigarettes for prompting or supporting cessation is limited (see Section 18B.7 for a detailed discussion of the effectiveness of e-cigarettes as a cessation aid).58  Evidence to date suggests that smokers who use e-cigarette intensively may be more likely to quit conventional cigarettes,92-96 however intermittent users—who comprise the majority of users—may be less likely to quit.92, 95 Quitting may also not be sustained over the longer term, with longitudinal research showing that dual users were more likely than smokers to quit smoking in the short term; however, this difference was lost by the 12- and 18-month marks.97 In the US, use of e-cigarettes by young adults is associated with more rather than less frequent and intensive cigarette smoking.98 E-cigarette use may also be associated with relapse among ex-smokers,99, 100 with one study finding intermittent users may be more likely to relapse to smoking than those who vape daily.101

Smoking poses a very significant risk to health both in the immediate and the longer term, but the most serious diseases emerge only with long-term use. While two of every three long term smokers in Australia will die from smoking, quitting prior to age 45 reduces mortality risk close to that of never smokers.102 Given that complete cessation of use of any nicotine product is the option associated with least harm, it follows that the optimal approach for younger smokers at least in the first instance would be to attempt to quit without continuing use of nicotine.

18B.6.5 The renormalisation of smoking

Decades of successful public health campaigning have profoundly denormalised smoking. As evidence has accumulated about the hazards of tobacco to smokers and non-smokers alike, stronger public health measures—including restrictions on smoking—have been widely adopted.103 Those advocating caution about e-cigarettes have characterised these new products as having the potential to weaken these tobacco control efforts and help to renormalise smoking.103, 104 E-cigarette use among young people is especially worrying if e-cigarettes promote the normalisation of nicotine use and smoking behaviour, and subsequently lead to long-term use among those who would otherwise never have vaped or smoked.57 Research in Hong Kong found that school-level e-cigarette use was associated with e-cigarette use susceptibility in never e-cigarette users, and with cigarette smoking susceptibility in never cigarette smokers,105 and a systematic review similarly found that social interactions and social norms could increase e-cigarette use, among both smokers and non-smokers.106

It has also been argued that e-cigarettes could revive the behaviour of smoking in public, undermining increasingly stringent restrictions on smoking in both indoor and outdoor areas.1 Dual users of e-cigarettes and cigarettes commonly report using the products to circumvent no-smoking policies,80, 81 and in the face of increasing restrictions on e-cigarette use in smokefree environments, many users report using e-cigarettes discreetly in places where such use is prohibited.107 However, it is unclear whether the growing acceptance and use of e-cigarettes affects acceptance of cigarette smoking, or regulations to discourage smoking.58 Research in the US found that one in five high school students who had never used tobacco products reported exposure to secondhand e-cigarette aerosol in public, which was associated with overestimation of peer use for both e-cigarettes and conventional cigarettes, as well as increased curiosity and susceptibility to e-cigarettes and cigarettes.108 On the other hand, some have argued that e-cigarettes are easily distinguishable in appearance and smell from tobacco cigarettes, and that widespread use of e-cigarettes is more likely to normalise alternative nicotine devices than smoking, and may benefit and support smokefree environments.6 Researchers in Great Britain found that positive perceptions of smoking attitudes among young people declined at a faster rate following the proliferation of e-cigarettes.76

Norms among adult smokers and vapers towards e-cigarettes appear to reflect country regulations, such that people in countries with less restrictive policies (England, Canada and the US) are exposed to more e-cigarette use in public and are more likely to report that society and people important to them approve of e-cigarette use compared with people in countries with more restrictive policies (Australia).109 Patterns are less clear among teenagers. Research in 2017 found that while young people in Canada, England, and the US had more pro-vaping than pro-smoking norms overall, English young people reported the most pro-smoking but least pro-vaping norms compared with Canadian and US teens.110

18B.6.6 Potential to reinvolve the tobacco industry in public health policy

Although e-cigarettes were originally developed and marketed independently from the tobacco industry, some of the world’s largest tobacco companies have heavily invested in the market—see Section 18B.1.3. Given its history of unethically promoting and defending tobacco cigarettes, the tobacco industry’s involvement in e-cigarettes is of great concern to public health experts. The tobacco industry is said to be pursuing five goals: promoting widespread dual use; hindering smoking cessation; renormalising public smoking; conveying to young people that nicotine is a benign drug; and welcoming back lapsed smokers.1 One paper concluded that there is little evidence to support claims that tobacco companies are moving away from the combustible cigarette market, and instead may be using investment in e-cigarettes to strategically position themselves as legitimate stakeholders in research and policy debates.111

Concerns have also been raised regarding the quality of research on e-cigarettes, with one systematic review finding many serious methodological shortcomings. In 34% of the papers reviewed, the authors had a conflict of interest. Most studies were funded or otherwise supported/influenced by manufacturers of e-cigarettes (including the tobacco industry), which appeared to influence the conclusions of the papers.112 Another analysis found that while almost all papers published on e-cigarettes and health without a conflict of interest found potentially harmful effects, less than eight per cent of tobacco industry-related studies reported potential harm. Tobacco industry papers were cited more often than papers written by independent researchers.113 A systematic review published in 2019 found that research funded by the e-cigarette, tobacco, or pharmaceutical industry was significantly associated with a supportive stance on tobacco harm reduction compared with non-industry funded articles.114

As well as enjoying commercial gains from investing in e-cigarettes, it has been argued that tobacco companies are likely to be keen to exploit opportunities for advertising and promotion that will promote tobacco and/or e-cigarette use.6 Many e-cigarette advertisements resemble traditional tobacco advertising.115 By becoming involved in alternative nicotine delivery products, companies may be able to evade current restrictions on engagement in policy imposed by Article 5.3 of the Framework Convention on Tobacco Control (FCTC).6 In response to concerns regarding the possibility of e-cigarettes interfering with existing tobacco control efforts, the WHO has invited FCTC Parties to “protect tobacco-control activities from all commercial and other vested interests related to [electronic nicotine delivery systems], including interests of the tobacco industry”.116

Relevant news and research

For recent news items and research on this topic, click  here. ( Last updated March 2020)

 

References 

1. Chapman S. Should electronic cigarettes be as freely available as tobacco cigarettes? No. British Medical Journal, 2013; 346:f3840. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23771038

2. Etter JF. Should electronic cigarettes be as freely available as tobacco? Yes. British Medical Journal, 2013; 346:f3845. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23771039

3. Kalkhoran S and Glantz SA. Modeling the health effects of expanding e-cigarette sales in the United States and United Kingdom: A Monte Carlo analysis. JAMA Internal Medicine, 2015; 175(10):1671-80. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26322924

4. Hajek P, Etter JF, Benowitz N, Eissenberg T, and McRobbie H. Electronic cigarettes: Review of use, content, safety, effects on smokers and potential for harm and benefit. Addiction, 2014; 109(11):1801-10. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25078252

5. Australian Institute of Health and Welfare. National Drug Strategy Household Survey detailed report: 2013. Cat. no. PHE 183 Canberra: AIHW, 2014. Available from: http://www.aihw.gov.au/publication-detail/?id=60129549469&tab=3.

6. Britton J and Bogdanovica I. Electronic cigarettes: A report commissioned by Public Health England.  2014. Available from: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/311887/Ecigarettes_report.pdf.

7. Barrington-Trimis JL, Urman R, Leventhal AM, Gauderman WJ, Cruz TB, et al. E-cigarettes, cigarettes, and the prevalence of adolescent tobacco use. Pediatrics, 2016; 138(2). Available from: https://www.ncbi.nlm.nih.gov/pubmed/27401102

8. Chaffee BW, Couch ET, and Gansky SA. Trends in characteristics and multi-product use among adolescents who use electronic cigarettes, United States 2011-2015. PLoS One, 2017; 12(5):e0177073. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28475634

9. Cullen KA, Ambrose BK, Gentzke AS, Apelberg BJ, Jamal A, et al. Notes from the field: Use of electronic cigarettes and any tobacco product among middle and high school students - United States, 2011-2018. Morbidity and Mortality Weekly Report, 2018; 67(45):1276-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30439875

10.   US Food & Drug Administration. Statement from FDA commissioner on launch of ‘the real cost’ youth e-cigarette prevention campaign amid evidence of sharply rising use among kids.  2018. Available from: https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm620791.htm

11.   Wang TW, Gentzke AS, Creamer MR, Cullen KA, Holder-Hayes E, et al. Tobacco product use and associated factors among middle and high school students - United States, 2019. MMWR Surveill Summ, 2019; 68(12):1-22. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31805035

12.   Mirbolouk M, Charkhchi P, Orimoloye OA, Uddin SMI, Kianoush S, et al. E-cigarette use without a history of combustible cigarette smoking among US adults: Behavioral risk factor surveillance system, 2016. Annals of Internal Medicine, 2019; 170(1):76-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30304466

13.   Owusu D, Huang J, Weaver SR, Pechacek TF, Ashley DL, et al. Patterns and trends of dual use of e-cigarettes and cigarettes among US adults, 2015-2018. Preventive Medicine Reports, 2019; 16:101009. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31763161

14.   Jongenelis MI, Brennan E, Slevin T, Kameron C, Jardine E, et al. Factors associated with intentions to use e-cigarettes among Australian young adult non-smokers. Drug Alcohol Rev, 2019; 38(5):579-87. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31317596

15.   Jankowski M, Lawson JA, Shpakou A, Poznanski M, Zielonka TM, et al. Smoking cessation and vaping cessation attempts among cigarette smokers and e-cigarette users in central and eastern Europe. International Journal of Environmental Research and Public Health, 2019; 17(1). Available from: https://www.ncbi.nlm.nih.gov/pubmed/31861455

16.   England LJ, Bunnell RE, Pechacek TF, Tong VT, and McAfee TA. Nicotine and the developing human: A neglected element in the electronic cigarette debate. American Journal of Preventive Medicine, 2015; 49(2):286-93. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25794473

17.   Klein JD. Electronic cigarettes are another route to nicotine addiction for youth. JAMA Pediatrics, 2015; 169(11):993-4. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26349006

18.   Goniewicz ML, Boykan R, Messina CR, Eliscu A, and Tolentino J. High exposure to nicotine among adolescents who use Juul and other vape pod systems ('pods'). Tobacco Control, 2019; 28(6):676-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30194085

19.   Willett JG, Bennett M, Hair EC, Xiao H, Greenberg MS, et al. Recognition, use and perceptions of JUUL among youth and young adults. Tobacco Control, 2019; 28(1):115-6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29669749

20.   Morean ME, Bold KW, Kong G, Gueorguieva R, Camenga DR, et al. Adolescents' awareness of the nicotine strength and e-cigarette status of JUUL e-cigarettes. Drug and Alcohol Dependence, 2019; 204:107512. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31487572

21.   Leigh NJ, Lawton RI, Hershberger PA, and Goniewicz ML. Flavourings significantly affect inhalation toxicity of aerosol generated from electronic nicotine delivery systems (ends). Tobacco Control, 2016; 25(Suppl 2):ii81-ii7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27633767

22.   Tierney PA, Karpinski CD, Brown JE, Luo W, and Pankow JF. Flavour chemicals in electronic cigarette fluids. Tobacco Control, 2016; 25(e1):e10-5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25877377

23.   Moore G, Hewitt G, Evans J, Littlecott HJ, Holliday J, et al. Electronic-cigarette use among young people in Wales: Evidence from two cross-sectional surveys. BMJ Open, 2015; 5(4):e007072. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25877272

24.   Singh T, Agaku IT, Arrazola RA, Marynak KL, Neff LJ, et al. Exposure to advertisements and electronic cigarette use among US middle and high school students. Pediatrics, 2016; 137(5). Available from: https://www.ncbi.nlm.nih.gov/pubmed/27244815

25.   Mantey DS, Cooper MR, Clendennen SL, Pasch KE, and Perry CL. E-cigarette marketing exposure is associated with e-cigarette use among US youth. The Journal of Adolescent Health, 2016; 58(6):686-90. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27080732

26.   Best C, Haseen F, van der Sluijs W, Ozakinci G, Currie D, et al. Relationship between e-cigarette point of sale recall and e-cigarette use in secondary school children: A cross-sectional study. BMC Public Health, 2016; 16(1):310. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27075888

27.   Pu J and Zhang X. Exposure to advertising and perception, interest, and use of e-cigarettes among adolescents: Findings from the US national youth tobacco survey. Perspect Public Health, 2017; 137(6):322-5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28379069

28.   Measham F, O’Brien K, and Turnbull G. “Skittles & red bull is my favourite flavour”: E-cigarettes, smoking, vaping and the changing landscape of nicotine consumption amongst British teenagers – implications for the normalisation debate. Drugs: Education, Prevention and Policy, 2016; 23(3):224-37. Available from: http://dx.doi.org/10.1080/09687637.2016.1178708

29.   Kong G, Morean ME, Cavallo DA, Camenga DR, and Krishnan-Sarin S. Reasons for electronic cigarette experimentation and discontinuation among adolescents and young adults. Nicotine & Tobacco Research, 2015; 17(7):847-54. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25481917

30.   Harrell MB, Weaver SR, Loukas A, Creamer M, Marti CN, et al. Flavored e-cigarette use: Characterizing youth, young adult, and adult users. Preventive Medicine Reports, 2017; 5:33-40. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27896041

31.   Pepper JK, Ribisl KM, and Brewer NT. Adolescents' interest in trying flavoured e-cigarettes. Tobacco Control, 2016; 25(Suppl 2):ii62-ii6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27633762

32.   Audrain-McGovern J, Rodriguez D, Pianin S, and Alexander E. Initial e-cigarette flavoring and nicotine exposure and e-cigarette uptake among adolescents. Drug and Alcohol Dependence, 2019; 202:149-55. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31351341

33.   Leventhal AM, Goldenson NI, Cho J, Kirkpatrick MG, McConnell RS, et al. Flavored e-cigarette use and progression of vaping in adolescents. Pediatrics, 2019; 144(5). Available from: https://www.ncbi.nlm.nih.gov/pubmed/31659004

34.   Morean ME, Butler ER, Bold KW, Kong G, Camenga DR, et al. Preferring more e-cigarette flavors is associated with e-cigarette use frequency among adolescents but not adults. PLoS One, 2018; 13(1):e0189015. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29300749

35.   Meernik C, Baker HM, Kowitt SD, Ranney LM, and Goldstein AO. Impact of non-menthol flavours in e-cigarettes on perceptions and use: An updated systematic review. BMJ Open, 2019; 9(10):e031598. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31619431

36.   Leventhal AM, Goldenson NI, Barrington-Trimis JL, Pang RD, and Kirkpatrick MG. Effects of non-tobacco flavors and nicotine on e-cigarette product appeal among young adult never, former, and current smokers. Drug and Alcohol Dependence, 2019; 203:99-106. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31434028

37.   Public Health (Tobacco) Act 2008 (NSW). s 29. See notice contained in New South Wales Government Gazette dated 15 January 2010, at 136.

38.   Public Health Act 1997 (TAS). s 68A(c)-(e).

39.   Tobacco and Other Smoking Products Act 1927 (ACT). s 21. See notice contained in Tobacco (Prohibited Smoking Products) Declaration 2011 (No 1) (Notifiable instrument NI2011-584).

40.   Tobacco and other Smoking Products Act 1998 (QLD). S 26zt.

41.   Tobacco Products Regulation Act 1997 (SA). s 34A. See notice contained in South Australian Government Gazette dated 10 August 2006, at 2640.

42.   Victorian Government Gazette No S 350. Order under section 15N of the Tobacco Act 1987: Banning the sale of certain products. 21 October 2011. Available from: http://www.gazette.vic.gov.au/gazette/Gazettes2011/GG2011S350.pdf

43.   US Food and Drug Administration (FDA). General questions and answers on the ban of cigarettes that contain certain characterizing flavors (edition 2). 2009. Available from: https://www.fda.gov/media/116681/download

44.   Farsalinos KE, Kistler KA, Gillman G, and Voudris V. Evaluation of electronic cigarette liquids and aerosol for the presence of selected inhalation toxins. Nicotine & Tobacco Research, 2015; 17(2):168-74. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25180080

45.   Allen JG, Flanigan SS, LeBlanc M, Vallarino J, MacNaughton P, et al. Flavoring chemicals in e-cigarettes: Diacetyl, 2,3-pentanedione, and acetoin in a sample of 51 products, including fruit-, candy-, and cocktail-flavored e-cigarettes. Environmental Health Perspectives, 2016; 124(6):733-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26642857

46.   Zhu SH, Sun JY, Bonnevie E, Cummins SE, Gamst A, et al. Four hundred and sixty brands of e-cigarettes and counting: Implications for product regulation. Tobacco Control, 2014; 23 Suppl 3:iii3-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24935895

47.   House Committee on Oversight and Reform. Examining juul’s role in the youth nicotine epidemic: Part i.  2019. Available from: https://oversight.house.gov/legislation/hearings/examining-juul-s-role-in-the-youth-nicotine-epidemic-part-i

48.   House Committee on Oversight and Reform. Examining juul’s role in the youth nicotine epidemic: Part ii.  2019. Available from: https://oversight.house.gov/legislation/hearings/examining-juul-s-role-in-the-youth-nicotine-epidemic-part-ii

49.  Lindblom EN. Effectively regulating e-cigarettes and their advertising—and the first amendment. Food & Drug Law Journal, 2015; 70:57–94. Available from: https://pubmed.ncbi.nlm.nih.gov/26292472/

50.   Krawitz M. We didn't start this fireless vapour: E-cigarette legislation in Australia. J Law Med, 2014; 22(2):462-81. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25715544

51.   US Food & Drug Administration. Statement from FDA commissioner on proposed new steps to protect youth by preventing access to flavored tobacco products and banning menthol in cigarettes. 2018. Available from: https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm625884.htm

52.   Gottlieb S. Statement from FDA commissioner on new enforcement actions and a youth tobacco prevention plan to stop youth use of, and access to, JUUL and other e-cigarettes. US Food & Drug Administration,  2018. Available from: https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm605432.htm

53.   Kelder SH, Mantey DS, Van Dusen D, Case K, Haas A, et al. A middle school program to prevent e-cigarette use: A pilot study of "catch my breath". Public Health Rep, 2020; 135(2):220-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31968177

54.   Schillo BA, Cuccia AF, Patel M, Simard B, Donovan EM, et al. JUUL in school: Teacher and administrator awareness and policies of e-cigarettes and JUUL in US middle and high schools. Health Promotion Practice, 2020; 21(1):20-4. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31530185

55.   Zhong J, Cao S, Gong W, Fei F, and Wang M. Electronic cigarettes use and intention to cigarette smoking among never-smoking adolescents and young adults: A meta-analysis. International Journal of Environmental Research and Public Health, 2016; 13(5). Available from: https://www.ncbi.nlm.nih.gov/pubmed/27153077

56.   Chatterjee K, Alzghoul B, Innabi A, and Meena N. Is vaping a gateway to smoking: A review of the longitudinal studies. International Journal of Adolescent Medicine and Health, 2016; 30(3). Available from: https://www.ncbi.nlm.nih.gov/pubmed/27505084

57.   National Academies of Sciences Engineering and Medicine. Public health consequences of e-cigarettes. The National Academies Press, Washington, DC 2018. Available from: http://nationalacademies.org/hmd/Reports/2018/public-health-consequences-of-e-cigarettes.aspx.

58.  Byrne S, Brindal E, Williams G, Anastasiou K, Tonkin A, et al. E-cigarettes, smoking and health. A literature review update. CSIRO, Australia,  2018. Available from: https://www.csiro.au/en/Research/BF/Areas/Nutrition-and-health/Public-health-and-wellbeing/Case-studies/E-cigarettes-report

59.   Asher T, Belden JL, Kelsberg G, and Safranek S. Does using e-cigarettes increase cigarette smoking in adolescents? J Fam Pract, 2019; 68(10):E12-E3. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31860706

60.   McCabe SE, West BT, and McCabe VV. Associations between early onset of e-cigarette use and cigarette smoking and other substance use among US adolescents: A national study. Nicotine & Tobacco Research, 2018; 20(8):923-30. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29986103

61.   Jongenelis MI, Jardine E, Kameron C, Rudaizky D, and Pettigrew S. E-cigarette use is associated with susceptibility to tobacco use among Australian young adults. Int J Drug Policy, 2019; 74:266-73. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31257041

62.   East K, Hitchman SC, Bakolis I, Williams S, Cheeseman H, et al. The association between smoking and electronic cigarette use in a cohort of young people. The Journal of Adolescent Health, 2018; 62(5):539-47. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29499983

63.   Aleyan S, Gohari MR, Cole AG, and Leatherdale ST. Exploring the bi-directional association between tobacco and e-cigarette use among youth in Canada. International Journal of Environmental Research and Public Health, 2019; 16(21). Available from: https://www.ncbi.nlm.nih.gov/pubmed/31683972

64.   Chaffee BW and Cheng J. Tobacco product initiation is correlated with cross-product changes in tobacco harm perception and susceptibility: Longitudinal analysis of the population assessment of tobacco and health youth cohort. Preventive Medicine, 2018; 114:72-8. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29913179

65.   Nicksic NE and Barnes AJ. Is susceptibility to e-cigarettes among youth associated with tobacco and other substance use behaviors one year later? Results from the PATH study. Preventive Medicine, 2019; 121:109-14. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30776386

66.   Park E, Livingston JA, Wang W, Kwon M, Eiden RD, et al. Adolescent e-cigarette use trajectories and subsequent alcohol and marijuana use. Addictive Behaviors, 2020; 103:106213. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31862618

67.   Wong SW, Lohrmann DK, Middlestadt SE, and Lin HC. Is e-cigarette use a gateway to marijuana use? Longitudinal examinations of initiation, reinitiation, and persistence of e-cigarette and marijuana use. Drug and Alcohol Dependence, 2020; 208:107868. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31981994

68.   Kim S and Selya AS. The relationship between electronic cigarette use and conventional cigarette smoking is largely attributable to shared risk factors. Nicotine & Tobacco Research, 2019. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31680169

69.   Liu G, Wasserman E, Kong L, and Foulds J. A comparison of nicotine dependence among exclusive e-cigarette and cigarette users in the PATH study. Preventive Medicine, 2017; 104:86-91. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28389330

70.   Barrington-Trimis JL, Urman R, Berhane K, Unger JB, Cruz TB, et al. E-cigarettes and future cigarette use. Pediatrics, 2016; 138(1). Available from: https://www.ncbi.nlm.nih.gov/pubmed/27296866

71.   Berry KM, Fetterman JL, Benjamin EJ, Bhatnagar A, Barrington-Trimis JL, et al. Association of electronic cigarette use with subsequent initiation of tobacco cigarettes in US youths. JAMA Netw Open, 2019; 2(2):e187794. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30707232

72.   Chien YN, Gao W, Sanna M, Chen PL, Chen YH, et al. Electronic cigarette use and smoking initiation in Taiwan: Evidence from the first prospective study in Asia. International Journal of Environmental Research and Public Health, 2019; 16(7). Available from: https://www.ncbi.nlm.nih.gov/pubmed/30935027

73.   Conner M, Grogan S, Simms-Ellis R, Flett K, Sykes-Muskett B, et al. Evidence that an intervention weakens the relationship between adolescent electronic cigarette use and tobacco smoking: A 24-month prospective study. Tobacco Control, 2019. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31253718

74.   Kinnunen JM, Ollila H, Minkkinen J, Lindfors PL, Timberlake DS, et al. Nicotine matters in predicting subsequent smoking after e-cigarette experimentation: A longitudinal study among Finnish adolescents. Drug and Alcohol Dependence, 2019; 201:182-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31238240

75.   Ip M and Middlekauff HR. Noncigarette tobacco products: Gateway or diversion? JAMA Pediatrics, 2018; 172(8):784. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29868766

76.   Hallingberg B, Maynard OM, Bauld L, Brown R, Gray L, et al. Have e-cigarettes renormalised or displaced youth smoking? Results of a segmented regression analysis of repeated cross sectional survey data in England, Scotland and Wales. Tobacco Control, 2020; 29(2):207-16. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30936390

77.   Levy DT, Warner KE, Cummings KM, Hammond D, Kuo C, et al. Examining the relationship of vaping to smoking initiation among US youth and young adults: A reality check. Tobacco Control, 2019; 28(6):629-35. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30459182

78.   Watkins SL, Glantz SA, and Chaffee BW. Noncigarette tobacco products-gateway or diversion?-reply. JAMA Pediatrics, 2018; 172(8):784-5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29868756

79.   Kristjansson AL, Allegrante JP, Sigfusson J, and Sigfusdottir ID. Do population trends in adolescent electronic cigarette use coincide with changes in prevalence of cigarette smoking? Preventive Medicine Reports, 2019; 15:100913. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31211028

80.   Robertson L, Hoek J, Blank ML, Richards R, Ling P, et al. Dual use of electronic nicotine delivery systems (ends) and smoked tobacco: A qualitative analysis. Tobacco Control, 2019; 28(1):13-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29419488

81.   Glasser AM, Collins L, Pearson JL, Abudayyeh H, Niaura RS, et al. Overview of electronic nicotine delivery systems: A systematic review. American Journal of Preventive Medicine, 2017; 52(2):e33-e66. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27914771

82.   Rahman MA, Hann N, Wilson A, and Worrall-Carter L. Electronic cigarettes: Patterns of use, health effects, use in smoking cessation and regulatory issues. Tobacco Induced Diseases, 2014; 12(1):21. Available from: http://www.biomedcentral.com/content/pdf/1617-9625-12-21.pdf

83.   Simonavicius E, McNeill A, Arnott D, and Brose LS. What factors are associated with current smokers using or stopping e-cigarette use? Drug and Alcohol Dependence, 2017; 173:139-43. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28246049

84.   Jackson SE, Hill E, Shahab L, Beard E, Michie S, et al. Prevalence and correlates of long-term e-cigarette and nicotine replacement therapy use: A prospective study in England. BMJ Open, 2019; 9(10):e029252. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31604784

85.   Jackson SE, Shahab L, West R, and Brown J. Associations between dual use of e-cigarettes and smoking cessation: A prospective study of smokers in England. Addictive Behaviors, 2020; 103:106230. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31841827

86.   Farsalinos KE and Polosa R. Safety evaluation and risk assessment of electronic cigarettes as tobacco cigarette substitutes: A systematic review. Ther Adv Drug Saf, 2014; 5(2):67-86. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25083263

87.   Oh AY and Kacker A. Do electronic cigarettes impart a lower potential disease burden than conventional tobacco cigarettes? Review on e-cigarette vapor versus tobacco smoke. Laryngoscope, 2014; 124(12):2702-6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25302452

88.   Chapman S. E-cigarettes: The best and the worst case scenarios for public health-an essay by simon chapman. British Medical Journal, 2014; 349:g5512. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25204397

89.   Hart C, Gruer L, and Bauld L. Does smoking reduction in midlife reduce mortality risk? Results of 2 long-term prospective cohort studies of men and women in Scotland. American Journal of Epidemiology, 2013; 178(5):770-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23825165

90.   Tverdal A and Bjartveit K. Health consequences of reduced daily cigarette consumption. Tobacco Control, 2006; 15(6):472-80. Available from: https://www.ncbi.nlm.nih.gov/pubmed/17130377

91.   Wang JB, Olgin JE, Nah G, Vittinghoff E, Cataldo JK, et al. Cigarette and e-cigarette dual use and risk of cardiopulmonary symptoms in the health eheart study. PLoS One, 2018; 13(7):e0198681. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30044773

92.   Biener L and Hargraves JL. A longitudinal study of electronic cigarette use among a population-based sample of adult smokers: Association with smoking cessation and motivation to quit. Nicotine & Tobacco Research, 2015; 17(2):127-33. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25301815

93.   Delnevo CD, Giovenco DP, Steinberg MB, Villanti AC, Pearson JL, et al. Patterns of electronic cigarette use among adults in the United States. Nicotine & Tobacco Research, 2016; 18(5):715-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26525063

94.   Hitchman SC, Brose LS, Brown J, Robson D, and McNeill A. Associations between e-cigarette type, frequency of use, and quitting smoking: Findings from a longitudinal online panel survey in Great Britain. Nicotine & Tobacco Research, 2015; 17(10):1187-94. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25896067

95.   Giovenco DP and Delnevo CD. Prevalence of population smoking cessation by electronic cigarette use status in a national sample of recent smokers. Addictive Behaviors, 2018; 76:129–34. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28802179

96.   Miller CR, Smith DM, and Goniewicz ML. Changes in nicotine product use among dual users of tobacco and electronic cigarettes: Findings from the population assessment of tobacco and health (PATH) study, 2013-2015. Substance Use and Misuse, 2020; 55(6):909-13. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31951489

97.   Sweet L, Brasky TM, Cooper S, Doogan N, Hinton A, et al. Quitting behaviors among dual cigarette and e-cigarette users and cigarette smokers enrolled in the tobacco user adult cohort. Nicotine & Tobacco Research, 2019; 21(3):278-84. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30346585

98.   Olfson M, Wall MM, Liu SM, Sultan RS, and Blanco C. E-cigarette use among young adults in the US. American Journal of Preventive Medicine, 2019; 56(5):655-63. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30885517

99.   Dai H and Leventhal AM. Association of electronic cigarette vaping and subsequent smoking relapse among former smokers. Drug and Alcohol Dependence, 2019; 199:10-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30978519

100. McMillen R, Klein JD, Wilson K, Winickoff JP, and Tanski S. E-cigarette use and future cigarette initiation among never smokers and relapse among former smokers in the PATH study. Public Health Rep, 2019; 134(5):528-36. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31419184

101. Brose LS, Bowen J, McNeill A, and Partos TR. Associations between vaping and relapse to smoking: Preliminary findings from a longitudinal survey in the UK. Harm Reduct J, 2019; 16(1):76. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31888637

102. Banks E, Joshy G, Weber MF, Liu B, Grenfell R, et al. Tobacco smoking and all-cause mortality in a large Australian cohort study: Findings from a mature epidemic with current low smoking prevalence. BMC Medicine, 2015; 13:38. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25857449

103. Fairchild AL, Bayer R, and Colgrove J. The renormalization of smoking? E-cigarettes and the tobacco "endgame". New England Journal of Medicine, 2014; 370(4):293-5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24350902

104. World Health Organization (WHO), Electronic nicotine delivery systems. Conference of the parties to the WHO Framework Convention on Tobacco Control Moscow, Russian Federation 2014. Available from: http://apps.who.int/gb/fctc/PDF/cop6/FCTC_COP6_10-en.pdf?ua=1.

105. Chen J, Ho SY, Leung LT, Wang MP, and Lam TH. School-level electronic cigarette use prevalence and student-level tobacco use intention and behaviours. Scientific Reports, 2019; 9(1):1690. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30737443

106. Amin S, Dunn AG, and Laranjo L. Social influence in the uptake and use of electronic cigarettes: A systematic review. American Journal of Preventive Medicine, 2020; 58(1):129-41. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31761515

107. Yingst JM, Lester C, Veldheer S, Allen SI, Du P, et al. E-cigarette users commonly stealth vape in places where e-cigarette use is prohibited. Tobacco Control, 2019; 28(5):493-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30097510

108. Agaku IT, Perks SN, Odani S, and Glover-Kudon R. Associations between public e-cigarette use and tobacco-related social norms among youth. Tobacco Control, 2020; 29(3):332-40. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31110159

109. Aleyan S, East K, McNeill A, Cummings KM, Fong GT, et al. Differences in norms towards the use of nicotine vaping products among adult smokers, former smokers and nicotine vaping product users: Cross-sectional findings from the 2016 ITC four country smoking and vaping survey. Addiction, 2019; 114 Suppl 1:97-106. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31062388

110. East KA, Hitchman SC, McNeill A, Thrasher JF, and Hammond D. Social norms towards smoking and vaping and associations with product use among youth in England, Canada, and the US. Drug and Alcohol Dependence, 2019; 205:107635. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31765990

111. Mathers A, Hawkins B, and Lee K. Transnational tobacco companies and new nicotine delivery systems. American Journal of Public Health, 2019; 109(2):227-35. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30571303

112. Pisinger C and Dossing M. A systematic review of health effects of electronic cigarettes. Preventive Medicine, 2014; 69:248-60. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25456810

113. Pisinger C, Godtfredsen N, and Bender AM. A conflict of interest is strongly associated with tobacco industry-favourable results, indicating no harm of e-cigarettes. Preventive Medicine, 2019; 119:124-31. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30576685

114. Hendlin YH, Vora M, Elias J, and Ling PM. Financial conflicts of interest and stance on tobacco harm reduction: A systematic review. American Journal of Public Health, 2019; 109(7):e1-e8. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31095414

115. Stanford University. Research into the impact of tobacco advertising: Cigs vs. Ecigs. Available from: http://tobacco.stanford.edu/tobacco_main/subtheme-comp.php?token=fm_tn_mt035.php

116. World Health Organization. Conference of the parties to the Framework Convention on Tobacco Control. Second report of Committee A. FCTC/COP/6/A/R/2, 2014. Available from: http://apps.who.int/gb/fctc/PDF/cop6/FCTC_COP6_AR2-en.pdf