Summary: For years, the debate over e-cigarettes has been clouded by claims of “mixed evidence.” However, a comprehensive new overview has moved to settle the score.
By pooling data from 14 systematic reviews conducted between 2014 and 2023, researchers found that nicotine-containing e-cigarettes are consistently more effective at helping people quit smoking than traditional nicotine replacement therapy (NRT) like patches, gum, or lozenges, as well as behavioral support alone. The study argues that while the evidence for quitting is now “clear and consistent,” significant gaps remain regarding long-term safety and data from low-income countries.
Key Facts
- Superior Success Rates: When looking at high-quality evidence, nicotine e-cigarettes repeatedly beat out non-nicotine versions, patches, and behavioral counseling for long-term smoking abstinence.
- The “Evidence Gap Map” (EGM): Researchers identified critical blind spots. We currently lack high-quality data comparing e-cigarettes to newer cessation aids like cytisine or nicotine pouches.
- Global Bias: Most current data comes from high-income countries. Researchers are calling for urgent studies in low- and middle-income nations to ensure these findings apply globally.
- Safety Inconclusive: While effective for quitting, the evidence regarding “serious adverse events” associated with long-term e-cigarette use remains inconclusive and requires continued primary research.
Source: Society for the Study of Addiction
A new overview of the best available evidence worldwide for smoking cessation has found that nicotine‑containing e‑cigarettes appear to be more effective for smoking cessation than other interventions such as nicotine replacement therapy (nicotine patches, gum, lozenges, etc.) e-cigarettes with no nicotine, and behavioural support.
This ‘overview’ of systematic reviews summarises existing evidence from several systematic reviews and makes the findings more accessible. The overview pooled the evidence from fourteen systematic reviews of smoking cessation interventions from 2014 to 2023.
Findings from higher-quality reviews consistently showed greater smoking cessation with nicotine-containing e‑cigarettes than other interventions. Lower-quality reviews produced more variable and imprecise estimates. When restricted to higher-quality evidence, results consistently favoured nicotine e‑cigarettes over nicotine replacement therapy, non-nicotine e-cigarettes, and other comparators.
The overview also created an ‘Evidence and Gap Map’ (EGM) to identify gaps in the current evidence that urgently need to be filled. There are currently no high-quality systematic reviews directly comparing nicotine e-cigarettes with cytisine, bupropion, or nicotine pouches. Also, direct evidence comparing nicotine e-cigarettes with varenicline is extremely limited, with only a single small trial at high risk of bias.
The EGM also showed that current evidence of serious adverse events associated with e-cigarettes is inconclusive, and that most of the studies collected data from high-income countries. Future primary research on e-cigarettes for smoking cessation should continue to collect data on serious adverse events and expand its data collection to include low-and middle-income countries.
Lead author DrAngela Difeng Wu, Senior Researcher and Lecturer at the Nuffield Department of Primary Care Health Sciences, University of Oxford, says “We hope this overview and Evidence and Gap Map can lay to rest some claims that evidence is ‘mixed’ regarding the impacts of nicotine e-cigarettes on smoking abstinence. In fact, the evidence is clear and consistent across all of the meta-analyses we consulted: e-cigarettes are effective at helping people stop smoking.”
Primary funding: This research work was funded by Cancer Research UK, Grant Number PRCPJT‐Nov22/100012.
Key Questions Answered:
A: Lead author Dr. Angela Difeng Wu notes that “mixed” claims often come from looking at lower-quality reviews with imprecise estimates. When you filter for high-quality, rigorous meta-analyses, the results are remarkably consistent: e-cigarettes help more people quit than traditional methods.
A: While this study confirms they are better for quitting cigarettes, it also highlights that evidence on “serious adverse events” is still inconclusive. The goal of using an e-cigarette in this context is as a cessation tool to stop inhaling combustible tobacco, which is known to be deadly.
A: That is one of the “gaps” identified. We don’t have enough head-to-head trials comparing e-cigarettes to these newer options yet. If you are looking for the “best available” evidence today, nicotine e-cigarettes are the current heavyweight champion.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our 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: The image is 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 considered a smoking cessation tool in some countries, such as the United Kingdom, but uncertainty remains internationally over whether their benefits outweigh potential harms when used for this purpose. This overview (1) synthesised existing evidence from systematic reviews (SR) on the effectiveness and safety of ECs to explore and address these uncertainties and disagreements and (2) mapped primary intervention studies to identify priorities for further research.
Methods
Overview of SRs published from 1 January 2015 and meeting the inclusion criteria of the Cochrane review of EC for smoking cessation. We searched seven databases to April 2024. We followed Cochrane screening and data extraction methods. We adapted Campbell Collaboration and 3ie methods for the Evidence and Gap Map (EGM). We assessed review quality using AMSTAR-2.
Results
We included 14 reviews of intervention studies (7 high quality; 7 low quality), with search dates from 2014 to 2023, in adult populations including the general population, people at risk of lung cancer, with comorbid health conditions and pregnant people. Eighteen studies were included across multiple reviews, some of which included multiple meta-analyses.
Across 21 meta-analytic comparisons of nicotine EC versus other interventions, all reported point estimates favouring nicotine EC for smoking cessation, with relative risks/odds ratios typically in the range 1.17–1.67 versus nicotine replacement therapy and 1.46–2.09 versus non-nicotine EC, with higher-quality reviews giving more consistent estimates.
Of 13 reviews that meta-analysed serious adverse events (SAEs), two reported point estimates suggesting increased SAEs with nicotine EC; other estimates included the possibility of no difference. For adverse events, pooled estimates generally indicated little or no difference between groups.
Our EGM mapped 90 primary, complete studies and identified absolute gaps in evidence comparing the effects of nicotine EC to cytisine, bupropion and nicotine pouches. Most studies used collected data from high-income countries.
Conclusion
Meta-analyses of electronic cigarettes (EC) for smoking cessation report point estimates favouring higher ≥6-month smoking cessation rates with nicotine EC compared with nicotine replacement therapy, non-nicotine EC/placebo, behavioural or no support and mixed support. Evidence on serious adverse events (SAEs) remains inconclusive. Evidence gaps were identified in SAE data and in studies from low- and middle-income countries.
