Nicotine is highly addictive. [12] [13] [14] Users become physically and psychologically dependent. [15] Scientists do not know how harmful e-cigarettes are over the long-term [16] [17] because it is hard to separate the effects of vaping from the effects of smoking when so many people both vape and smoke. [note 4] [18] E-cigarettes have not been used widely enough or for long enough to be sure. [19] [20] [21] Data from two states in the Pregnancy Risk Assessment System (PRAMS) show that in 2015—roughly the mid-point of the study period—10.8% of the sample used e-cigarettes in the three months prior to the pregnancy while 7.0%, 5.8%, and 1.4% used these products at the time of the pregnancy, in the first trimester, and at birth respectively. [106] According to National Health Interview Survey (NHIS) data from 2014 to 2017, 38.9% of pregnant smokers used e-cigarettes compared to only 13.5% of non-pregnant, reproductive age women smokers. [107] A health economic study found that passing an e-cigarette minimum legal sale age law in the United States increased teenage prenatal smoking by 0.6 percentage points and had no effect on birth outcomes. [108] Nevertheless, additional research needs to be done on the health effects of electronic cigarette use during pregnancy. [109] Baenziger, Olivia; Ford, Laura; Yazidjoglou, Amelia; Joshy, Grace; Banks, Emily (2021). "E-cigarette use and combustible tobacco cigarette smoking uptake among non-smokers, including relapse in former smokers: umbrella review, systematic review and meta-analysis". BMJ Open. 11 (3): e045603. doi: 10.1136/bmjopen-2020-045603. ISSN 2044-6055. PMC 8011717. PMID 33785493.

Jimenez Ruiz, CA; Solano Reina, S; de Granda Orive, JI; Signes-Costa Minaya, J; de Higes Martinez, E; Riesco Miranda, JA; Altet Gómez, N; Lorza Blasco, JJ; Barrueco Ferrero, M; de Lucas Ramos, P (August 2014). "The electronic cigarette. Official statement of the Spanish Society of Pneumology and Thoracic Surgery (SEPAR) on the efficacy, safety and regulation of electronic cigarettes". Archivos de Bronconeumologia. 50 (8): 362–7. doi: 10.1016/j.arbres.2014.02.006. PMID 24684764. a b c d e f g Orellana-Barrios, Menfil A.; Payne, Drew; Mulkey, Zachary; Nugent, Kenneth (2015). "Electronic cigarettes-a narrative review for clinicians". The American Journal of Medicine. 128 (7): 674–81. doi: 10.1016/j.amjmed.2015.01.033. ISSN 0002-9343. PMID 25731134. Dautzenberg, B.; Adler, M.; Garelik, D.; Loubrieu, J.F.; Mathern, G.; Peiffer, G.; Perriot, J.; Rouquet, R.M.; Schmitt, A.; Underner, M.; Urban, T. (2017). "Practical guidelines on e-cigarettes for practitioners and others health professionals. A French 2016 expert's statement". Revue des Maladies Respiratoires. 34 (2): 155–164. doi: 10.1016/j.rmr.2017.0In one of the few studies identified, a 2015 survey of 316 pregnant women in a Maryland clinic found that the majority had heard of e-cigarettes, 13% had used them, and 0.6% were current daily users. [85] These findings are of concern because the dose of nicotine delivered by e-cigarettes can be as high or higher than that delivered by traditional cigarettes. [85] Pax Labs has developed vaporizers that heats the leaves of tobacco to deliver nicotine in a vapor. [408] [409] In June 2015, they introduced Juul a type of e-cigarette which delivers 10 times as much nicotine as other e-cigarettes, equivalent to an actual cigarette puff. [385] Juul was spun off from Pax Labs in June 2017 and is now available by the independent company Juul Labs. [410] The eTron 3T from Vapor Tobacco Manufacturing, launched in December 2014, [411] employs a patented, aqueous system whereby the tobacco is extracted into water. [412] The e-liquid contains organic tobacco, organic glycerin, and water. [411]

Linda Bauld; Kathryn Angus; Marisa de Andrade (May 2014). "E-cigarette uptake and marketing" (PDF). Public Health England. UK. pp.1–19. Companies should not be able to claim that e-cigarettes are a cessation aid unless they are approved by the FDA for that purpose...There is not yet enough evidence for clinicians to counsel their patients who are using combustible tobacco products to use e-cigarettes as a primary cessation aid. The association will continue to monitor the evidence concerning e-cigarettes as cessation devices to determine whether they might be integrated into comprehensive cessation strategies. For patients with existing cardiovascular disease and stroke, or at risk of a cardiovascular disease event, intensive cessation counseling should be offered as soon as possible." [27]Marques, Patrice; Piqueras, Laura; Sanz, Maria-Jesus (December 2021). "An updated overview of e-cigarette impact on human health". Respiratory Research. 22 (1): 151. doi: 10.1186/s12931-021-01737-5. PMC 8129966. PMID 34006276. S2CID 234753956. the safety of e-cigarette consumption and its potential as a smoking cessation method remain controversial due to limited evidence...the potential long-term effects of e-cigarette consumption have been scarcely investigated. Consumers have shown passionate support for e-cigarettes that other nicotine replacement products did not receive. [119] They have a mass appeal that could challenge combustible tobacco's market position. [119] a b c d e f g h Bhatnagar, Aruni; Whitsel, Laurie P.; Ribisl, Kurt M.; Bullen, Chris; Chaloupka, Frank; Piano, Mariann R.; Robertson, Rose Marie; McAuley, Timothy; Goff, David; Benowitz, Neal (14 October 2014) [Published online 24 August 2014]. "Electronic Cigarettes: A Policy Statement From the American Heart Association". Circulation. 130 (16): 1418–1436. doi: 10.1161/CIR.0000000000000107. PMC 7643636. PMID 25156991. a b c Cai, Hua; Wang, Chen (2017). "Graphical review: The redox dark side of e-cigarettes; exposure to oxidants and public health concerns". Redox Biology. 13: 402–406. doi: 10.1016/j.redox.2017.05.013. ISSN 2213-2317. PMC 5493817. PMID 28667909.

E-cigarettes create vapor that consists of fine and ultrafine particles of particulate matter, with the majority of particles in the ultrafine range. [83] The vapor have been found to contain propylene glycol, glycerin, nicotine, flavors, small amounts of toxicants, [83] carcinogens, [129] and heavy metals, as well as metal nanoparticles, and other substances. [83] Many carcinogenic compounds have been detected in e-cigarettes, such as N-Nitrosonornicotine (NNN), N-Nitrosoanatabine (NAT), etc., all of which have been proven to be harmful to human health. [186] Exactly what the vapor consists of varies in composition and concentration across and within manufacturers, and depends on the contents of the liquid, the physical and electrical design of the device, and user behavior, among other factors. [2] McNeill, A; Brose, LS; Calder, R; Bauld, L; Robson, D (February 2018). "Evidence review of e-cigarettes and heated tobacco products 2018" (PDF). Public Health England. UK. pp.1–243. Wilder, Natalie; Daley, Claire; Sugarman, Jane; Partridge, James (April 2016). "Nicotine without smoke: Tobacco harm reduction". Royal College of Physicians. UK. pp.1–191. There is low quality evidence that vaping assists smokers to quit smoking in the long-term compared with nicotine-free vaping. [162] Nicotine-containing e-cigarettes were associated with greater effectiveness for quitting smoking than e-cigarettes without nicotine. [163] A 2013 study in smokers who were not trying to quit, found that vaping, with or without nicotine decreased the number of cigarettes consumed. [164] E-cigarettes without nicotine may reduce tobacco cravings because of the smoking-related physical stimuli. [118]Also known as an e-cig, vaporizer, vape pen, hookah pen, e-pipe, or, formally, electronic nicotine delivery system ( ENDS). [1]