Published in 2020 by researchers at the University of California San Diego, this study used data from the Population Assessment of Tobacco and Health (PATH) Study, a large longitudinal study tracking tobacco use and health outcomes across the United States.

The researchers compared quit rates between smokers who used e-cigarettes and carefully matched control smokers who did not use e-cigarettes, following both groups over time. They found no statistically significant difference in quit rates between the two groups, meaning that in the real world (outside of clinical trials), e-cigarette use did not appear to help smokers quit.

The authors concluded that among smokers in the United States, e-cigarette use does not increase smoking cessation in naturalistic settings and may actually be associated with reduced tobacco abstinence. This contrasts with findings from randomized trials, suggesting that how people use e-cigarettes in everyday life differs from the structured support provided in clinical research settings.

Published in The Lancet Respiratory Medicine in 2016, this systematic review and meta-analysis focused on real-world and clinical settings rather than randomized controlled trials alone. The researchers analyzed observational studies examining whether e-cigarette users were more or less likely to quit smoking than non-users.

The meta-analysis found that the odds of quitting cigarettes were 28% lower among smokers who used e-cigarettes compared to those who did not. This finding held across multiple studies and settings, suggesting that in everyday use, e-cigarettes may actually reduce the likelihood of quitting rather than increase it.

The authors argued that e-cigarettes as currently promoted and used should not be recommended as effective smoking cessation aids until evidence emerges showing that real-world use patterns lead to actual quitting. The disconnect between clinical trial results and observational data remains one of the most debated issues in tobacco control.

Published in Nicotine and Tobacco Research, this longitudinal study tracked people who used both cigarettes and e-cigarettes (dual users) over the course of one year to see what happened to their smoking behavior.

At the one-year follow-up, the results showed that dual use rarely leads to full smoking cessation. Of the initial dual users, 43.9% had returned to smoking only (abandoning e-cigarettes), 48.8% continued using both products, only 5.9% had fully switched to vaping only, and just 1.4% had quit both products entirely.

These findings suggest that for most people who start vaping while still smoking, the e-cigarette does not serve as a bridge to quitting. Instead, the most common outcomes are either going back to cigarettes alone or maintaining long-term dual use, which means continued exposure to the harms of combustible tobacco.

The same 2019 New England Journal of Medicine randomized trial frequently cited as evidence for e-cigarette effectiveness also revealed a concerning pattern: among those who successfully quit smoking in the e-cigarette group, 80% were still using e-cigarettes at the one-year follow-up. In contrast, only 9% of successful quitters in the nicotine replacement therapy group were still using their assigned product.

This means the e-cigarette group did not achieve nicotine freedom - they transferred their nicotine dependence from cigarettes to e-cigarettes. While vaping is generally considered less harmful than smoking, the goal of cessation is typically to become nicotine-free, not to maintain addiction through a different delivery device.

Critics argue this high rate of continued e-cigarette use demonstrates that vaping creates its own dependence rather than serving as a true cessation tool. The long-term health effects of indefinite e-cigarette use remain unknown, and users may be exposed to harmful chemicals for decades.

In 2019, the Centers for Disease Control and Prevention identified a nationwide outbreak of e-cigarette or vaping product use-associated lung injury (EVALI) across the United States. By February 2020, 2,807 people had been hospitalized and 68 deaths were confirmed.

Patients presented with severe respiratory symptoms including shortness of breath, cough, chest pain, and in many cases required intensive care and mechanical ventilation. Vitamin E acetate, a chemical added to some THC-containing vaping products, was identified as the primary causative agent, though other chemicals in vaping products may also have contributed.

While the outbreak was most strongly associated with THC-containing products from informal sources rather than commercial nicotine e-cigarettes, it demonstrated that inhaling aerosolized chemicals carries inherent risks. The incident highlighted that e-cigarettes are not harmless devices, and that the long-term effects of inhaling vaporized chemicals daily remain poorly understood.

Published by the American Heart Association in 2023, this scientific statement reviewed the existing literature on the cardiopulmonary effects of e-cigarettes and vaping products. The statement was developed by a panel of cardiovascular and pulmonary researchers.

The panel found moderate-strength evidence that e-cigarette use causes adverse cardiovascular effects including increased blood pressure, arterial stiffness, oxidative stress, endothelial dysfunction (damage to blood vessel linings), and increased platelet aggregation. Nicotine e-cigarette aerosols contain reactive oxygen species that can damage cells and organs, potentially leading to cardiovascular disease over time.

The statement noted that while e-cigarettes generally produce fewer toxicants than combustible cigarettes, they are not harmless. For people who switch from smoking to long-term vaping rather than quitting nicotine entirely, the cumulative cardiovascular effects over decades of use are unknown and potentially significant.

The US Centers for Disease Control and Prevention (CDC) maintains that e-cigarettes have not been approved by the Food and Drug Administration (FDA) as a smoking cessation device. The CDC recommends that smokers who want to quit use FDA-approved cessation medications such as varenicline (Chantix), bupropion (Wellbutrin), or nicotine replacement therapies (patches, gum, lozenges) combined with behavioral counseling.

The CDC notes that while some adult smokers have completely switched from cigarettes to e-cigarettes, the scientific evidence is not yet sufficient for the CDC to recommend e-cigarettes for quitting. The agency emphasizes that most e-cigarette users continue to smoke regular cigarettes (dual use), which provides little to no health benefit.

This position reflects the regulatory reality in the United States, where no e-cigarette manufacturer has received FDA marketing authorization specifically for smoking cessation claims, unlike products such as nicotine patches and gum that have undergone formal clinical trials and received FDA approval for this indication.

Published in the European Respiratory Journal in 2025, this systematic review specifically investigated the impact of dual use (simultaneous use of both cigarettes and e-cigarettes) on smoking cessation outcomes.

The review found that the majority of smokers who take up e-cigarettes do not transition to complete smoking cessation. Instead, they tend to maintain dual use for extended periods, continuing to smoke at reduced but still harmful levels while also vaping. The prolonged dual-use pattern was the most common outcome across multiple studies.

The authors emphasized that from a health perspective, dual use offers minimal benefit compared to quitting both products. Even substantial reductions in cigarette consumption do not eliminate most of the health risks of smoking, as cardiovascular risk in particular does not decline proportionally with reduced cigarette numbers. The review concluded that promoting e-cigarettes as cessation aids may inadvertently encourage prolonged dual use rather than complete cessation.

The 2018 National Academies of Sciences, Engineering, and Medicine report on e-cigarettes reviewed longitudinal studies tracking young people over time. The committee concluded there is "substantial evidence" of a causal relationship between e-cigarette use and the transition from never smoking to trying cigarettes.

Multiple longitudinal studies consistently showed that adolescents and young adults who used e-cigarettes were significantly more likely to later initiate combustible cigarette smoking compared to peers who never vaped. This gateway effect raises concerns that while e-cigarettes might help some adult smokers quit, they simultaneously create new nicotine-addicted users among people who would otherwise never have smoked.

From a population-level perspective, critics argue that any net cessation benefit among adult smokers may be partially or fully offset by the new nicotine users created through youth vaping initiation. If e-cigarettes are marketed and perceived as cessation tools, this legitimization may inadvertently increase their appeal to non-smoking youth.