Summary: For years the debate over e-cigarettes has been muddied by claims of “mixed evidence.” A new, comprehensive overview of systematic reviews aims to clarify the picture.
By synthesizing findings from 14 systematic reviews published between 2014 and 2023, researchers conclude that nicotine-containing e-cigarettes consistently outperform traditional nicotine replacement therapy (NRT) — such as patches, gum, or lozenges — and behavioural support alone for helping people quit smoking. The overview finds the evidence for cessation is clear and consistent across high-quality reviews, while noting important gaps in long-term safety data and in research from low- and middle-income countries.
Key Facts
- Higher quit rates: High-quality reviews repeatedly show greater long-term smoking abstinence with nicotine e-cigarettes compared with non-nicotine devices, NRT, and counselling-only approaches.
- Evidence and Gap Map (EGM): The study mapped the existing evidence and identified key blind spots — notably a lack of high-quality comparisons between nicotine e-cigarettes and newer cessation aids such as cytisine or nicotine pouches.
- Geographic bias: Most primary studies come from high-income countries. The authors call for urgent trials in low- and middle-income settings to determine whether the findings generalize globally.
- Safety uncertain: Evidence on serious adverse events linked to e-cigarette use is inconclusive; more primary research with robust safety monitoring is needed.
Source: Society for the Study of Addiction
Overview findings
This overview of systematic reviews brings together the best available evidence on e-cigarettes as tools for smoking cessation. It pooled and evaluated fourteen systematic reviews of cessation interventions conducted between 2014 and 2023. The authors assessed review quality and separated higher-quality meta-analyses from lower-quality ones to provide a clearer summary of the evidence.
When the analysis focused on higher-quality reviews, nicotine-containing e-cigarettes consistently showed greater effectiveness in achieving long-term (generally ≥6 months) abstinence from smoking than nicotine replacement therapy, non-nicotine e-cigarettes, and behavioural supports. Lower-quality reviews produced more variable or imprecise estimates, which helps explain why some earlier summaries appeared inconsistent.
To guide future research, the overview produced an Evidence and Gap Map (EGM). The EGM revealed a lack of head-to-head, high-quality evidence comparing nicotine e-cigarettes with treatments such as cytisine, bupropion, and nicotine pouches. Direct comparisons with varenicline are extremely limited, relying on one small trial at high risk of bias.
On safety, 13 reviews meta-analysed serious adverse events (SAEs). Most pooled estimates found little or no difference between groups, but two reviews reported point estimates suggesting increased SAEs with nicotine e-cigarettes. Overall, SAE evidence remains inconclusive and requires continued collection of rigorous safety data in primary studies.
The EGM mapped 90 primary intervention studies. The majority of these studies were conducted in high-income countries, highlighting the need for trials in low- and middle-income regions to ensure broad applicability of the findings.
Lead author Dr Angela Difeng Wu, Senior Researcher and Lecturer at the Nuffield Department of Primary Care Health Sciences, University of Oxford, commented that the overview and EGM should reduce confusion over claims of “mixed” evidence. She emphasised that when higher-quality meta-analyses are examined, results consistently favour nicotine e-cigarettes for smoking abstinence.
Primary funding: This research was funded by Cancer Research UK, Grant Number PRCPJT‐Nov22/100012.
Key Questions Answered:
A: The authors note that claims of mixed results often stem from lower-quality reviews that produce imprecise or inconsistent estimates. When analyses are restricted to high-quality meta-analyses, the effect favouring nicotine e-cigarettes becomes consistent and reliable.
A: The overview confirms nicotine e-cigarettes are effective as cessation aids, but it does not resolve the question of long-term safety. The purpose of using e-cigarettes in this context is to help people stop inhaling combustible tobacco, which carries well-established, severe health risks. More research is needed on serious adverse events associated with e-cigarette use.
A: These are identified as evidence gaps. There are few or no high-quality systematic reviews directly comparing nicotine e-cigarettes with cytisine, bupropion, nicotine pouches, or modern trials versus varenicline. Until such head-to-head trials are completed, nicotine e-cigarettes remain the most consistently supported option among the interventions compared in the current evidence base.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was added by the editorial staff.
About this addiction research news
Author: Jean O’Reilly
Source: Society for the Study of Addiction
Contact: Jean O’Reilly – Society for the Study of Addiction
Image: Image credited to Shamsi Lab, NYU College of Dentistry
Original Research: Open access.
“Electronic Cigarettes for Smoking Cessation: An Overview of Systematic Reviews and Evidence and Gap Map” by Angela Difeng Wu, Monserrat Conde, Ailsa R. Butler, Ethan Knight, Nicola Lindson, Jonathan Livingstone-Banks, Peter Hajek, Hayden McRobbie, Rachna Begh, Annika Theodoulou, Caitlin Notley, Tari Turner, Eliza Zhitnik, Jamie Hartmann-Boyce. Addiction
DOI: 10.1111/add.70388
Abstract
Electronic Cigarettes for Smoking Cessation: An Overview of Systematic Reviews and Evidence and Gap Map
Background and aims
Electronic cigarettes (EC) are used as smoking cessation aids in some countries, including the United Kingdom, but international debate continues over whether their benefits outweigh potential harms. This overview (1) synthesised systematic review evidence on EC effectiveness and safety to address ongoing uncertainties and disagreements, and (2) mapped primary intervention studies to identify research priorities.
Methods
The overview included systematic reviews published from 1 January 2015 that met inclusion criteria similar to those used in the Cochrane review of EC for smoking cessation. Seven databases were searched to April 2024. The study followed Cochrane screening and data extraction methods, adapted Evidence and Gap Map methods from the Campbell Collaboration and 3ie, and assessed review quality using AMSTAR-2.
Results
Fourteen reviews of intervention studies were included (seven rated high quality and seven low quality), with searches spanning 2014–2023. The populations covered adults in the general population, people at elevated lung cancer risk, those with comorbid conditions, and pregnant people. Across reviews, eighteen primary studies appeared repeatedly in multiple analyses, with several meta-analyses combining overlapping trial data.
Across 21 meta-analytic comparisons of nicotine EC versus other interventions, every comparison reported point estimates favouring nicotine EC for smoking cessation. Relative effect sizes typically ranged from approximately 1.17–1.67 versus nicotine replacement therapy and 1.46–2.09 versus non-nicotine EC, with higher-quality reviews providing the most consistent estimates.
Of 13 reviews that meta-analysed serious adverse events, two reported point estimates suggesting increased SAEs with nicotine EC while other analyses included the possibility of no difference. For non-serious adverse events, pooled estimates generally indicated little or no difference between groups.
The Evidence and Gap Map identified 90 primary, complete studies and highlighted absolute gaps in evidence comparing nicotine EC to cytisine, bupropion, and nicotine pouches. Most primary studies were conducted in high-income countries.
Conclusion
Meta-analyses of e-cigarettes for smoking cessation report point estimates that favour higher ≥6-month quit rates with nicotine e-cigarettes compared with nicotine replacement therapy, non-nicotine e-cigarettes/placebo, behavioural support, or no support. Evidence on serious adverse events remains inconclusive. Crucial evidence gaps exist in SAE reporting and in trials conducted in low- and middle-income countries, which should be priorities for future research.