The study, published in Addiction and led by researchers at the Nuffield Department of Primary Care Health Sciences, brought together findings from 14 systematic reviews published between 2014 and 2023. In total, the team examined evidence from 109 primary studies and created an Evidence and Gap Map to show where research is strong and where important gaps remain.
Across the higher-quality reviews, the findings were consistent: nicotine e-cigarettes were more effective for smoking cessation than other interventions. These higher-quality reviews are those that followed more rigorous methods - such as using comprehensive search strategies, carefully assessing the risk of bias in included studies, and applying appropriate statistical analyses - making their findings more reliable.
By contrast, lower-quality reviews, which did not meet all of these standards, produced more mixed and less precise results.
Dr Angela Difeng Wu, Senior Researcher and Lecturer at the Nuffield Department of Primary Care Health Sciences, said:
“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.”
The review also found that evidence on serious adverse events remains inconclusive. While some analyses suggested a possible increase in serious adverse events, the estimates were generally imprecise and based on relatively few events. For most other adverse events, the evidence suggested little or no difference between nicotine e-cigarettes and comparison treatments.
The authors identified several important gaps in the evidence. There is currently no high-quality systematic review directly comparing nicotine e-cigarettes with cytisine, bupropion or nicotine pouches. Evidence comparing nicotine e-cigarettes with varenicline is also extremely limited. The researchers say future studies should continue to collect data on serious adverse events and include more evidence from low- and middle-income countries.
The paper, 'Electronic Cigarettes for Smoking Cessation: An Overview of Systematic Reviews and Evidence and Gap Map', is published in Addiction and is open access.