A sweeping analysis of global evidence suggests nicotine e-cigarettes may outperform traditional quit aids, but lingering safety uncertainties and research gaps keep the debate far from settled.
Study: Electronic cigarettes for smoking cessation: An overview of systematic reviews and evidence and gap map. Image credit: StockLab/Shutterstock.com
Electronic cigarettes, or vapes, are often offered to help people quit the smoking habit, but there is ongoing uncertainty, particularly around safety, suggesting benefits for smoking cessation. A recent review published in Addiction pulls together existing studies to assess the safety and effectiveness of vaping for this purpose, identifies remaining gaps, and outlines the design for future primary intervention studies.
How e-cigarettes deliver nicotine without burning tobacco
Vapes are electronic cigarettes that produce an aerosol by heating an e-liquid contained in a pod, a cartridge that can be replaced or refilled. The liquid may contain nicotine and other flavors, or be non-nicotine.
Smoking is currently still the leading preventable cause of cancer, death, and higher disease rates among the underprivileged, globally and in the UK. Vapes pose less risk for these outcomes than tobacco cigarettes, according to health organizations and professional associations.
However, the role played by vaping in helping people quit smoking is still debated internationally, despite growing meta-analytic evidence supporting its effectiveness, and it is important for consumers, healthcare providers, and regulatory authorities.
Overview of 14 systematic reviews and 109 studies
The current study was designed to systematically review existing reviews, synthesize and summarize the evidence, and make it readily accessible. The researchers aimed to extend the evidence presented by the Cochrane living systematic review (LSR) of ECs for smoking cessation.
The researchers included 14 systematic reviews of intervention studies published after 2015. These covered 109 primary studies. The reviews were equally split between higher- and lower-quality reviews, with most available evidence coming from high-income countries.
The population samples included the general population, pregnant women, people with other existing conditions, and people with high lung cancer risk. These reviews often covered the same material, though not entirely.
In addition, they created an Evidence and Gap Map (EGM), a web-based tool that visually depicts where evidence is missing in a given research area, helping frame policy and direct research.
Vaping may outperform NRT
There were 21 meta-analyses comparing vaping with other nicotine replacement therapies (NRT). All showed that nicotine vapes favored smoking cessation compared to the others. For instance, cessation risk was raised by 17–67 % with nicotine vapes, compared to various nicotine replacement therapies like skin patches or gum.
The direction of effect was consistently favorable across all studies. When only high-quality evidence was considered, the evidence points in the same direction.
Despite this, it is important to note that statistical uncertainty exists across multiple reviews, with some confidence intervals suggesting little or no difference. The authors note publication bias, unacceptable methodology, small sample sizes, and other technical flaws in several of the reviews.
Nicotine vape–NRT combinations
A single high-quality review compared nicotine vapes combined with NRT versus NRT alone, as well as nicotine vapes combined with NRT versus non-nicotine vapes combined with NRT. These analyses showed greater efficacy for nicotine vape–NRT combinations compared with NRT alone or non-nicotine combinations. This was contradicted by a lower-quality review that suggested no statistically significant difference.
Vaping versus placebo
Nicotine vaping appeared to be more beneficial than a placebo in smoking cessation, across studies, irrespective of quality. The results indicate that compared to placebo, nicotine vapes increased cessation rates, in some analyses appearing to more than triple them, although some estimates were imprecise with wide confidence intervals.
Vaping versus behavioral or no support
Nicotine vapes were more effective than behavioral support or no support, but non-nicotine vapes did not show this benefit, with estimates often compatible with either benefit or no clear difference.
In addition, only one small, low-quality trial directly compared nicotine vapes with varenicline (a drug used to support smoking cessation). This trial suggested varenicline may be more effective, but was limited by small size and high risk of bias. Indirect evidence did not show a clear difference between the two.
Safety of nicotine vapes
Adverse events were not consistently increased compared to NRT, placebo, non-nicotine vapes, vape–NRT combinations, or heated tobacco, across studies. The review revealed a mixed picture, mainly due to a few reported events and imprecise reporting. Nicotine vapes were possibly associated with a small increase in adverse events compared to behavioral support or no support.
Evidence gaps persist for key cessation drug comparisons
The EGM revealed that evidence is mostly available on comparative efficacy of nicotine vapes to support smoking cessation at six months or more, versus NRT and versus behavioral support or no support. There was little evidence of nicotine vapes versus cytisine, bupropion, and nicotine pouches.
Evidence on physiological outcomes (such as heart rate, blood pressure, and toxicant exposure) was limited and largely derived from a small subset of studies, with uneven reporting across the evidence base.
Strengths and limitations
Despite the rigorous study methods used for this systematic review, in line with Cochrane reviews, some limitations exist, including the grouping of single and combined nicotine replacement therapies for comparison, the omission of studies published after April 2024, and the exclusion of ongoing studies from the Evidence and Gap Map in accordance with standard practice.
Nicotine vapes show consistent advantage for quitting
Overall, the studies showed a clear tendency to benefit smoking cessation for at least six months with the use of nicotine vapes, compared to several common cessation approaches, including NRT, placebo/non-nicotine vapes, and behavioral support.
Our hope is that this overview and EGM can lay to rest some claims that evidence is ‘mixed’ regarding the impacts of ECs on smoking abstinence, given the clear consistency of results across meta-analyses.
Evidence across socioeconomic and geographic variations is limited, with few studies from low- and middle-income countries. Studies identifying serious adverse events yielded inconsistent results.
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