Electronic cigarettes are often marketed as a method to assist smokers to quit, or as a ‘safe alternative’ to conventional tobacco cigarettes. There is currently insufficient evidence to support these claims. This statement explains the current evidence, to assist consumers and policy-makers.
Table of contents
- E-cigarettes may expose users to fewer toxic chemicals than conventional tobacco cigarettes; however the extent to which this reduces harm to the user has not been determined.
- E-cigarettes may expose users to chemicals and toxins such as formaldehyde, heavy metals, particulate matter and flavouring chemicals, at levels that have the potential to cause adverse health effects.
- There is currently insufficient evidence to conclude whether e-cigarettes can assist smokers to quit. Smokers wishing to quit should consult the Quitline or their general practitioner.
- There is some evidence from longitudinal studies to suggest that e-cigarette use in non-smokers is associated with future uptake of tobacco cigarette smoking.
- Health authorities and policy-makers should act to minimise harm to users and bystanders, and to protect vulnerable groups such as young people, until evidence of safety, quality and efficacy can be produced.
- NHMRC is currently funding a number of studies into the safety and efficacy of e-cigarettes.
- Consumers should seek further information about e-cigarettes from reliable sources, such as the relevant State or Territory Health Department or quit smoking services.
E-cigarettes are battery operated devices that heat a liquid (called ‘e-liquid’) to produce a vapour that users inhale. Although the composition of this liquid varies, it typically contains a range of chemicals, including solvents and flavouring agents, and may or may not contain nicotine. E-cigarettes have evolved as a product group since first entering the market, with products now ranging from early ‘first generation’ devices that resemble cigarettes, to second and third generation devices that enable users to modify characteristics of the device, such as adjusting the voltage.1
This wide variation in products, and the ability of users to customise their vaping experience, makes it difficult to assess the safety and efficacy of e-cigarettes as a group, because the results from research involving one particular product may not be applicable to all e-cigarettes or all users. However, by examining the evidence to identify common findings across a range of different products, or results that are replicated in a number of studies, it is possible to gain some insight into the efficacy of e-cigarettes, their potential harms, and areas where further research is required.
NHMRC recognises the need for high-quality research in this area and is currently funding a number of studies investigating the effects of e-cigarettes.
The following information is provided to assist consumers and policy-makers in understanding the current evidence about the safety and efficacy of e-cigarettes. This information is current at the time of writing but is subject to change as more research becomes available.
Health and safety
Potential health risks
It is widely believed that e-cigarettes are likely to be less harmful than tobacco cigarettes, because they expose users to fewer toxic chemicals.2, 3, 4 However, there is insufficient evidence to quantify the reduction in risk when e-cigarettes are used instead of tobacco cigarettes.1, 5 Although a 2014 study reported that e-cigarettes are 95% less harmful than tobacco cigarettes,6 this finding was based on opinion rather than empirical evidence, and concerns have been raised about potential conflicts of interest.7, 8 The World Health Organisation has stated that “no specific figure about how much ‘safer’ the use of these products is compared to smoking can be given any scientific credibility at this time.”1
E-cigarettes are not likely to be risk free, and may expose users to chemicals and toxins at levels that have the potential to cause health effects. These include solvents such as propylene glycol, glycerol or ethylene glycol, which may form toxic or cancer-causing compounds when vaporised.9, 10, 11, 12, 13, 14, 15, 16, 17 Although these chemicals are typically found in lower concentrations than in tobacco cigarettes,3, 4, 10, 15 in some studies e-cigarettes and tobacco cigarettes were found to produce similar levels of formaldehyde,11, 14 which is classified as a cancer-causing agent.18 E-cigarette liquids or vapour may also contain potentially harmful chemicals which are not present in smoke from tobacco cigarettes.1, 11, 19
While some of the chemicals in e-liquid are also used in food production and are generally considered safe when eaten, this does not mean that these chemicals are safe when inhaled as a vapour directly into the lungs. A number of studies have reported harmful effects when certain flavourings that are approved for use in food production, including cherry, cinnamon and popcorn flavours, are inhaled.20, 21, 22, 23 There is growing evidence to suggest that the long-term inhalation of flavourings used in most e-liquids is likely to pose a risk to health.1 Studies also show that e-cigarettes expose both users and bystanders to particulate matter (very small particles)16, 24, 25, 26, 27 that may worsen existing illnesses or increase the risk of developing diseases such as cardiovascular or respiratory disease.28 The World Health Organisation has warned that exposure to any level of particulate matter may be harmful and that levels of exposure should be minimised.29 E-cigarettes may also expose users to metals such as aluminium, arsenic, chromium, copper, lead, nickel and tin,3, 15, 30, 31, 32 with these elements having been detected in e-liquid and in the vapour produced during use. In some cases these metals have been detected at levels greater than, or similar to, those found in tobacco cigarettes.1, 30 Adverse events
Studies that have tested e-cigarettes for use as a smoking cessation tool found that users of e-cigarettes typically experience a low rate of adverse events in the short term,33, 34 with mouth and throat irritation the most commonly reported symptoms. However, more serious adverse events have also been reported, with over 200 incidents of e-cigarettes overheating, catching fire or exploding reported to date in the US and UK alone.35 In some cases, these events have resulted in life‑threatening injury, permanent disfigurement or disability, and major property damage. The rising popularity of e-cigarette use internationally has also corresponded with an increasing number of reported nicotine poisonings due to exposure to or ingestion of e-liquids.36, 37, 38, 39, 40, 41, 42 The effects of exposure range from relatively mild, including irritation of the eyes and skin, nausea and vomiting,36, 37, 40 to severe life-threatening illness,39 and in some cases, death.36, 38, 42 Passive exposure
A recent systematic review of 16 studies concluded that e-cigarette vapour has the potential to pose a health risk to bystanders, although the risk is likely to be lower than that posed by conventional cigarette smoke.43 However, exposure to certain metals such as nickel and silver may be greater for e-cigarettes than tobacco cigarettes.43 A 2016 study found that the most common symptoms reported by those passively exposed to e-cigarettes included respiratory difficulties, eye irritation, headache, nausea and sore throat or throat irritation.44
Experts disagree about whether e-cigarettes may help smokers to quit, or whether they will become ‘dual users’ of both e-cigarettes and tobacco cigarettes. There is currently insufficient evidence to demonstrate that e-cigarettes are effective in assisting people to quit smoking1 and no brand of e-cigarette has been approved by the Therapeutic Goods Administration (TGA) for this purpose.
Although a 2016 systematic review conducted by the Cochrane Collaboration33 found some evidence that e-cigarettes with nicotine may assist smokers to quit, the review authors had a low level of confidence in this finding, due to the small volume of evidence.
The review also reported results from one study comparing e-cigarettes with nicotine replacement therapy, which found that both methods resulted in similar rates of smoking cessation at 6 months follow-up. However, the reviewers noted that more research is required to enable confidence in these estimates and that further research is likely to change the estimate of effect.33
Smokers wishing to quit are advised to consult their general practitioner. First-line treatments include a range of TGA-approved nicotine replacement therapies and prescription medications that have been tested for safety and efficacy. Support and information are also available from the Quitline (13 78 48) or via the Quit Now website (www.quitnow.gov.au).
E-cigarettes and tobacco control policies
Concerns have been raised that the potential benefits of e-cigarettes in reducing harm to smokers may be outweighed by the risks that they may undermine tobacco control efforts. This includes the potential for e-cigarettes to provide a gateway to nicotine addiction or tobacco product use, or that they may renormalise smoking.
The appeal of flavoured e-cigarettes to children and adolescents is also of concern, with studies reporting rapid uptake of e-cigarettes among adolescents in many countries, where trend data are available.45, 46, 47, 48, 49 This provides some cause for concern given uncertainties about the long-term safety of e-cigarettes. There is some evidence that e-cigarettes could act as a gateway into nicotine addiction or tobacco cigarette smoking. A number of longitudinal studies have reported an association between e-cigarette use in non-smokers and the uptake of tobacco cigarette smoking in the future.50, 51, 52, 53 This association remained even when the studies controlled for other risk factors that might make people more likely to take up smoking. In some studies, the effect of e-cigarettes on future smoking behaviour was greatest among those who were otherwise at low risk of taking up smoking.51, 54
A number of studies have also reported an association between e-cigarette use in non‑users and future use of marijuana52 or tobacco products such as hookahs, cigars or pipes.51, 55, 56 In view of the above concerns, the World Health Organisation has recommended that policy-makers act to prevent the initiation of e-cigarette use by non-smokers and youth, with special attention given to protecting vulnerable groups.1
The manufacturing quality of e-cigarettes is highly variable, with a number of issues relating to quality control reported in the literature. Labelling of e-cigarettes and e-liquids has been found to be incomplete or inaccurate.57, 58 Products have been found to contain chemicals that were not listed on the label,57, 58, 59 or to state incorrectly that they did not contain potentially toxic chemicals, despite analyses confirming their presence.60, 61 There may also be wide variation between the levels of nicotine declared on packaging and the amount contained in e-liquid.9, 58, 62, 63, 64, 65 One study that compared identical models of e-cigarettes found that nicotine content varied by up to 20% when the products came from different manufacturing batches, with variation of up to 12% reported for products manufactured in the same batch.66 Furthermore, some products that are labelled as nicotine free have been found to contain nicotine.11, 15, 57, 59, 62, 65, 67, 68
When seeking information about e-cigarettes online, it is important to look at websites that provide a reliable source of information, such as government websites or quit smoking services. Information on websites sponsored by retailers or manufacturers may reflect a commercial interest in promoting the sale of certain products. Similarly, when reading published research on e-cigarettes it is important to consider whether the authors of the research held any conflicts of interest that could potentially bias their findings, or whether the research was funded by an organisation with a financial interest in the outcomes, such as e-cigarette manufacturers.69
The following websites may provide further information of use to consumers:
World Health Organisation – Electronic Nicotine Delivery Systems and Electronic Non-Nicotine Delivery Systems (ENDS/ENNDS)
Information, fact sheets and FAQs from government departments
ACT Health – Electronic Cigarettes
New South Wales Department of Health – Electronic Cigarettes
Product Safety Australia – Electronic Cigarette Safety
Therapeutic Goods Administration – Electronic Cigarettes
Western Australia Department of Health – Electronic cigarettes (e-cigarettes)
State and Territory Health Departments – Contact Details
Australian Medical Association – Tobacco Smoking and E-cigarettes (2015) – The AMA Position
Cancer Council Australia and The Heart Foundation – Joint Position Statement on Electronic Cigarettes
Public Health Association of Australia – Statement by the Public Health Associations of Australia on Electronic Cigarettes
1 World Health Organisation, “Electronic Nicotine Delivery Systems and Electronic Non-Nicotine Delivery Systems (ENDS/ENNDS)” WHO Framework Convention on Tobacco Control, Geneva, 2016.
2 World Health Organisation, “Electronic Nicotine Delivery Systems” WHO Framework Convention on Tobacco Control, Geneva, 2014.
3 M. L. Goniewicz , J. Knysak , M. Gawron, L. Kosmider, A. Sobczak and J. Kurek, “Levels of Selected Carcinogens and Roxicants in Vapour from Electronic Cigarettes” Tobacco Control, vol. 23, no. 2, pp. 133-139, 2014.
4 S. S. Hecht, S. G. Carmella, D. Kotandeniya, M. E. Pillsbury, M. Chen, B. W. Ransom, R. Isaksson Vogel, E. Thompson, S. E. Murphy and D. K. Hatsukami, “Evaluation of Toxicant and Carcinogen Metabolites in the Urine of e-Cigarette Users Versus Cigarette Smokers” Nicotine & Tobacco Research, pp. 1-6, 2014.
5 N. Lindson-Hawley, J. Hartmann-Boyce, T. R. Fanshawe, R. Begh, A. Farley and T. Lancaster, “Interventions to Reduce Harm from Continued Tobacco Use” Cochrane Database of Systematic Reviews, no. 10, 2016.
6 D. J. Nutt, L. D. Phillips, D. Balfour, H. V. Curran, M. Dockrell, J. Foulds, K. Fagerstrom, K. Letlape, A. Milton, R. Polosa, J. Ramsey and D. Sweanor, “Estimating the Harms of Nicotine-Containing Products Using the MCDA Approach” European Addiction Research, vol. 20, no. 5, pp. 218-225, 2014.
7 The Lancet, “Public Health England’s Evidence-Based Confusion” The Lancet, vol. 386, p. 829, 2015.
8 M. Mckee and S. Capewell, “Evidence about Electronic Cigarettes: Foundation Built on Rock or Sand?” BMJ, vol. 351, 2015.
9 T. Cheng, “Chemical Evaluation of Electronic Cigarettes” Tobacco Control, vol. 23, no. Suppl 2, pp. ii11-7, 2014.
10 O. Geiss, I. Bianchi and J. Barrero-Moreno, “Correlation of Volatile Carbonyl Yields Emitted by E-cigarettes with the Temperature of the Heating Coil and the Perceived Sensorial Quality of the Generated Vapours” International Journal of Hygiene and Environmental Health, vol. 219, no. 3, pp. 268-277, 2016.
11 C. Hutzler, M. Paschke, S. Kruschinski, F. Henkler, J. Hahn and A. Luch, “Chemical Hazards Present in Liquids and Vapors of Electronic Cigarettes” Archives of Toxicology, vol. 88, pp. 1295-1308, 2014.
12 R. P. Jensen, W. Luo, J. F. Pankow, R. M. Strongin and D. H. Peyton, “Hidden Formaldehyde in E-cigarette Aerosols” The New England Journal of Medicine, vol. 372, no. 4, pp. 392-394, 2015.
13 M. Sleiman, J. M. Logue, V. N. Montesinos, M. L. Russell, M. I. Litter, L. A. Gundel and H. Destaillats, “Emissions from Electronic Cigarettes: Key Parameters Affecting the Release of Harmful Chemicals” Environmental Science & Technology, vol. 50, no. 17, pp. 9644-9651, 2016.
14 L. Kosmider, A. Sobczak, M. Fik, J. Knysak, M. Zaciera, J. Kurek and M. L. Goniewicz, “Carbonyl Compounds in Electronic Cigarette Vapors – Effects of Nicotine Solvent and Battery Output Voltage” Nicotine & Tobacco Research, vol. 16, no. 10, pp. 1319-1326, 2014.
15 W. Visser, L. Geraets, W. Klerx, L. Hernandez, E. Stephens, E. Croes, P. Schwillens, H. Cremers, P. Bos and R. Talhout, “The Health Risks of Using E-cigarettes” National Institute for Public Health and the Environment, Bilthoven, 2015.
16 A. El-Hellani, R. Salman, R. El-Hage, S. Talih, N. Malek, R. Baalbaki, N. Karaoghlanian, R. Nakkash, A. Shihadeh and N. A. Saliba, “Nicotine and Carbonyl Emissions From Popular Electronic Cigarette Products: Correlation to Liquid Composition and Design Characteristics” Nicotine & Tobacco Research, vol. Oct, 2016.
17 A. Khlystov and V. Samburova, “Flavoring Compounds Dominate Toxic Aldehyde Production during E-Cigarette Vaping” Environmental Science & Technology, vol. 50, no. 23, pp. 13080-13085, 2016.
18 International Agency for Research on Cancer (IARC), “IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol 100F (29)” WHO, 2012.
19 S. Uchiyama, K. Ohta, Y. Inaba and N. Kunungita, “Determination of Carbonyl Compounds Generated from the E-cigarette using Coupled Silica Cartridges Impregnated with Hydroquinone and 2,4-Dinitrophenylhydrazine, Followed by High‑Performance Liquid Chromatography” Analytical Sciences, vol. 29, pp. 1219-1222, 2013. 20 K. Kreiss, A. Gomaa, G. Kullman, K. Fedan, E. Simoes and P. Enright, “Clinical Bronchiolitis Obliterans in Workers at a Microwave-Popcorn Plant” New England Journal of Medicine, vol. 347, no. 5, pp. 330-338, 2002.
21 P. Harber, K. Saechao and C. Boomus, “Diacetyl-Induced Lung Disease” Toxicological Reviews, vol. 25, no. 4, pp. 261-272, 2006.
22 R. Behar, B. Davis, Y. Wang, V. Bahl, S. Lin and P. Talbot, “Identification of Toxicants in Cinnamon-Flavored Electronic Cigarette Refill Liquids” Toxicology in Vitro, vol. 28, no. 2, pp. 198-208, 2014.
23 L. Kosmider, A. Sobczak, A. Prokopowicz, J. Kurek, M. Zaciera, J. Knysak, D. Smith and M. L. Goniewicz, “Cherry-flavoured Electronic Cigarettes Expose Users to the Inhalation Irritant, Benzaldehyde” Thorax, vol. 71, no. 4, pp. 376-377, 2016.
24 R. M. Pellegrino, B. Tinghino, G. Mangiaracina, A. Marani, M. Vitali, C. Protano, J. F. Osborn and M. S. Cattaruzza, “Electronic Cigarettes: an Evaluation of Exposure to Chemicals and Fine Particulate Matter (PM)” Annali di Igiene, vol. 24, no. 4, pp. 279-288, 2012.
25 W. Schober, K. Szendrei, W. Matzen, H. Osiander-Fuchs, D. Heitmann, T. Schettgen, R. A. Jorres and H. Fromme, “Use of Electronic Cigarettes (E-cigarettes) Impairs Indoor Air Quality and Increases FeNO Levels of E-cigarette Consumers” International Journal of Hygiene and Environmental Health, vol. 217, pp. 628-637, 2014. 26 T. Schripp, D. Markewitz, E. Uhde and T. Salthammer, “Does E-cigarette Consumption Cause Passive Vaping?” Indoor Air, vol. 23, pp. 25-31, 2013.
27 J. Zhao, G. Pyrgiotakis and P. Demokritou, “Development and Characterization of Electronic-Cigarette Exposure Generation System (Ecig-EGS) for the Physico-Chemical and Toxicological Assessment of Electronic Cigarette Emissions” Inhalation Toxicology, vol. 28, no. 14, pp. 658-669, 2016.
28 Environmental Protection Agency, “Integrated Science Assessment for Particulate Matter (Final Report)” U.S. Environmental Protection Agency, Washington DC, 2009.
29 World Health Organisation, “WHO Air Quality Guidelines for Particulate Matter, Ozone, Nitrogen Dioxide and Sulfur Dioxide: Summary of Risk Assessment” WHO, Geneva, 2006.
30 M. Williams, A. Villarreal, K. Bozhilov, S. Lin and P. Talbot, “Metal and Silicate Particles Including Nanoparticles are Present in Electronic Cigarette Cartomizer Fluid and Aerosol” PLoS One, vol. 8, no. 3, p. e57987, 2013.
31 V. B. Mikheev, M. C. Brinkman, C. A. Granville, S. M. Gordon and P. I. Clark, “Real-Time Measurement of Electronic Cigarette Aerosol Size Distribution and Metals Content Analysis” Nicotine & Tobacco Research, vol. May, 2016.
32 C. A. Hess, P. Olmedo, A. Navas-Acien, W. Goessler, J. E. Cohen and A. M. Rule, “E-cigarettes as a Source of Toxic and Potentially Carcinogenic Metals” Environmental Research, vol. 152, pp. 221-225, 2017.
33 J. Hartmann-Boyce, H. McRobbie, C. Bullen, R. Begh, L. F. Stead and P. Hajek, “Electronic Cigarettes for Smoking Cessation (Review)” Cochrane Database of Systematic Reviews, no. 9, 2016.
34 M. R. Gualano, S. Passi, F. Bert, G. La Torre, G. Scaioli and R. Siliquini, “Electronic Cigarettes: Assessing the Efficacy and the Adverse Effects through a Systematic Review of Published Studies” Journal of Public Health, vol. 37, no. 3, pp. 488-497, 2015.
35 S. F. Rudy and E. L. Durmowicz, “Electronic Nicotine Delivery Systems: Overheating, Fires and Explosions” Tobacco Control, vol. Mar, 2016.
36 K. Chatham-Stephens, R. Law, E. Taylor, S. Kieszak, P. Melstrom, R. Bunnell, B. Wang, H. Day, B. Apelberg, L. Cantrell, H. Foster and J. G. Schier, “Exposure Calls to U. S. Poison Centers Involving Electronic Cigarettes and Conventional Cigarettes‑September 2010-December 2014” Journal of Medical Toxicology, 2016.
37 F. Davanzo, L. Settimi, G. Milanesi, F. Giordano, F. M. Sesana, A. Celentano, E. Urbani, G. Panzavolta, L. Cossa, A. Tomoiaga, A. Travaglia and V. Dimasi, “Surveillance of Hazardous Exposures to Electronic Cigarettes in Italy” Clinical Toxicology, vol. 52, no. Supp, pp. 336-337, 2014.
38 A. Kamboj, H. A. Spiller, M. J. Casavant, T. Chounthirath and G. A. Smith, “Pediatric Exposure to E-Cigarettes, Nicotine, and Tobacco Products in the United States” Pediatrics, vol. 137, no. 6, 2016.
39 S. W. Lindberg, N. Ebbehoej, J. Bang and L. B. Christensen, “Nicotine Poisoning Related to the Use of E-cigarettes” Clinical Toxicology, vol. 53, no. 4, 2015.
40 S. Pajarre-Sorsa, M. Saukkonen and K. Hoppu, “Calls Concerning Electronic Cigarettes to the Finnish Poison Information Centre” Clinical Toxicology, vol. 52, no. Supp, p. 337, 2014.
41 E. Thomas, R. A. Spears, G. Alldridge, C. V. Krishna, J. P. Thompson, M. Eddleston, J. A. Vale and S. H. L. Thomas, “E-cigarette Liquid Refills – a Safe Beverage? Analysis of Enquiries to the UK National Poisons Information Service from 2007 to 2013” Clinical Toxicology, vol. 52, no. Supp, pp. 338-339, 2014.
42 J. P. Vakkalanka, L. S. Hardison and C. P. Holstege, “Epidemiological Trends in Electronic Cigarette Exposures Reported to U.S. Poison Centers” Clinical Toxicology, vol. 52, no. 5, pp. 542-548, 2014.
43 I. M. R. Hess, K. Lachireddy and A. Capon, “A Systematic Review of the Health Risks from Passive Exposure to Electronic Cigarette Vapour” Public Health Research and Practice, vol. 26, no. 2, 2016.
44 E. L. Durmowicz, S. F. Rudy and I. L. Chen, “Electronic Cigarettes: Analysis of FDA Adverse Experience Reports in Non users” Tobacco Control, vol. 25, no. 2, p. 242, 2016.
45 S. Lee, R. Grana and S. Glantz, “Eletronic Cigarette Use Among Korean Adolescents: A Cross-Sectional Study of Market Penetration, Dual Use, and Relationship to Quit Attempts and Former Smoking” J Adolesc Health, vol. 54, pp. 684-690, 2014.
46 B. Eastwood, M. J. Dockrell, D. Arnott, J. Britton, H. Cheeseman, M. J. Jarvis and A. McNeill, “Electronic Cigarette Use in Young People in Great Britain 2013-2014” Public Health, vol. 129, no. 9, pp. 1150-1156, 2015.
47 T. Singh, R. A. Arrazola, C. G. Corey, C. G. Husten, L. J. Neff, D. M. Homa and B. A. King, “Tobacco Use Among Middle and High School Students — United States, 2011-2015” Morbidity and Mortality Weekly Report, vol. 65, no. 14, 2016.
48 J. White, J. Li, R. Newcombe and D. Walton, “Tripling Use of Electronic Cigarettes Among New Zealand Adolescents Between 2012 and 2014” The Journal of Adolescent Health, vol. 56, no. 5, pp. 522-528, 2015.
49 J. M. Kinnunen, H. Ollila, P. L. Lindfors and A. H. Rimpelä, “Changes in Electronic Cigarette Use from 2013 to 2015 and Reasons for Use Among Finnish Adolescents” International Journal of Environmental Research and Public Health, vol. 13, no. 11, 2016.
50 K. Chatterjee, B. Alzghoul, A. Innabi and N. Meena, “Is Vaping a Gateway to Smoking: a Review of the Longitudinal Studies” Int J Adolesc Med Health, 2016.
51 J. L. Barrington-Trimis, R. Urman, K. Berhane, J. B. Unger, T. B. Cruz, M. A. Pentz, J. M. Samet, A. M. Leventhal and R. McConnell, “E-Cigarettes and Future Cigarette Use” Pediatrics, vol. 138, no. 1, 2016.
52 J. B. Unger, D. W. Soto and A. Leventhal, “E-cigarette Use and Subsequent Cigarette and Marijuana Use Among Hispanic Young Adults” Drug and Alcohol Dependence, 2016.
53 T. R. Spindle, M. M. Hiler, M. E. Cooke and T. Eissenberg, “Electronic Cigarette Use and Uptake of Cigarette Smoking: A Longitudinal Examination of U.S. College Students” Addictive Behaviors, vol. 67, pp. 66-72, 2017.
54 T. A. Wills, J. D. Sargent, F. X. Gibbons, I. Pagano and R. Schweitzer, “E-cigarette Use is Differentially Related to Smoking Onset Among Lower Risk Adolescents” Tobacco Control, 2016.
55 J. Huh and A. M. Leventhal, “Progression of Poly-Tobacco Product Use Patterns in Adolescents” American Journal of Preventive Medicine, vol. 51, no. 4, pp. 513-517, 2016.
56 A. M. Leventhal, D. R. Strong, M. G. Kirkpatrick, J. B. Unger, S. Sussman, N. R. Riggs, M. D. Stone, R. Khoddam, J. M. Samet and J. Audrain-McGovern, “Association of Electronic Cigarette Use with Initiation of Combustible Tobacco Product Smoking in Early Adolescence” JAMA, vol. 314, no. 7, pp. 700-707, 2015.
57 J. Hahn, Y. B. Monakhova, J. Hengen, M. Kohl-Himmelseher, J. Schassler, H. Hahn, T. Kuballa and D. W. Lachenmeier, “Electronic Cigarettes: Overview of Chemical Composition and Exposure Estimation” Tobacco Induced Diseases, vol. 12, no. 1, p. 23, 2014.
58 S. Han, H. Chen, X. Zhang, T. Liu and Y. Fu, “Levels of Selected Groups of Compounds in Refill Solutions for Electronic Cigarettes” Nicotine & Tobacco Research, vol. 18, no. 5, pp. 708-714, 2016.
59 M. E. Hadwiger, M. L. Trehy, W. Ye, T. Moore, J. Allgire and B. Westenberger, “Identification of Amino-tadalafil and Rimonabant in Electronic Cigarette Products Using High Pressure Liquid Chromatography with Diode Array and Tandem Mass Spectrometric Detection” Journal of Chromatography, vol. 1217, no. 48, pp. 7547-7555, 2010.
60 J. G. Allen, S. S. Flanigan, M. LeBlanc, J. Vallarino, P. MacNaughton, J. H. Stewart and D. C. Christiani, “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, 2015.
61 Australian Competition and Consumer Commission, “ACCC Takes Action Against E-cigarette Suppliers for Alleged Misleading “No Toxic Chemicals” Claims” 20 June 2016. Online. Available: https://www.accc.gov.au/media-release/accctakes- action-against-e-cigarette-suppliers-for-alleged-misleading-%E2%80%9Cno-toxic-chemicals%E2%80%9D-claims. Accessed 25 November 2016.
62 K. Buettner-Schmidt, D. R. Miller and N. Balasubramanian, “Electronic Cigarette Refill Liquids: Child-Resistant Packaging, Nicotine Content, and Sales to Minors” Journal of Pediatric Nursing, vol. 31, no. 4, pp. 373-379, 2016.
63 B. Davis, M. Dang, J. Kim and P. Talbot, “Nicotine Concentrations in Electronic Cigarette Refill and Do-it-yourself Fluids” Nicotine & Tobacco Research, vol. 17, no. 2, pp. 134-141, 2015.
64 M. Williams, A. Villareal, B. Davis and P. Talbot, “Comparison of the Performance of Cartomizer Style Electronic Cigarettes from Major Tobacco and Independent Manufacturers” PLoS One, vol. 11, no. 2, 2016.
65 M. Famele, J. Palmisani, C. Ferranti, C. Abenavoli, L. Palleschi, R. Mancinelli, R. M. Fidente, G. de Gennaro and R. Draisci, “Liquid Chromatography with Tandem Mass Spectrometry Method for the Determination of Nicotine and Minor Tobacco Alkaloids in Electronic Cigarette Refill Liquids and Second-hand Generated Aerosol” Journal of Separation Science, vol. Dec, 2016.
66 M. L. Goniewicz, P. Hajek and H. McRobbie, “Nicotine Content of Electronic Cigarettes, its Release in Vapour and its Consistency Across Batches: Regulatory Implications” Addiction, vol. 109, no. 3, pp. 500-507, 2014.
67 U.S. Food and Drug Administration, “Evaluation of E-cigarettes” U.S. Food and Drug Administration, St Louis, MO, 2009.
68 J. Regueiro, A. Giri and T. Wenzl, “Optimization of a Differential Ion Mobility Spectrometry-Tandem Mass Spectrometry Method for High-Throughput Analysis of Nicotine and Related Compounds: Application to Electronic Cigarette Refill Liquids” Analytical Chemistry, vol. 88, no. 12, pp. 6500-6508, 2016.
69 C. Pisinger and M. Døssing, “A Systematic Review of Health Effects of Electronic Cigarettes” Preventive Medicine, vol. 69, pp. 248-260, 2014.