One concern about giving smokers e-cigarettes as a smoking cessation aid is that doing so instantly converts them into dual users (smoking both cigarettes and e-cigarettes), which adds the risks of e-cigarette use to cigarette use. Peter Hajek’s group just published Patterns of e-Cigarette Use and Smoking Cessation Outcomes: Secondary Analysis of a Large Randomised Controlled Trial to Inform Clinical Advice to reassure clinicians and smokers that this is not a problem.
The new paper presents additional analysis of the data reported in his group’s 2019 randomized trial of e-cigarettes versus nicotine-replacement therapy for cessation to conclude, “Dual use was associated with a reduction in smoking and quitting smoking later on.”
Whether this is an accurate summary of what their results show is not clear because they did not do statistical testing of the one year results due to small numbers.
The more important thing they ignore, however, is that providing e-cigarettes as a cessation aid produced 3.7 dual users for everyone who stopped smoking cigarettes. From the data in Table 2 of their new paper, among smokers who were provided e-cigarettes as a cessation aid, 17 of 107 dual users at 1 week had stopped smoking at 1 year. That means that 180 were dual users at 1 year. That number compares with 49 smokers who had stopped smoking (from Table 2 of their earlier paper). That gives 180/49=3.7 dual users for every smoker who stopped cigarettes.
In addition to not presenting this fact, they minimize the importance of continued dual use, “reassuring those worried about dual use that such use is associated with reduced smoking.” While they did find lower cigarette consumption among ongoing dual users, they ignored a meta-analysis of 19 studies conducted by FDA scientists that “did not find any significant difference in all-cause mortality, all-cancer risks, and smoking-/tobacco-related cancer risk among those who reduced.”
The Hajek group did not compare their findings to the relevant literature
An important element of any scientific paper is to summarize the relevant literature and relate your findings to that literature. The Hajek group ignored a 2024 systematic review of 16 longitudinal studies, 8 of which could be pooled in a meta-analysis (identified in February 2023) that found “Current evidence suggests that DU is not a first step towards smoking cessation, with most DU [dual use] continuing cigarette consumption either through persistent DU or exclusive CC [conventional cigarette] smoking. Relatively fewer DU transitioned into complete nicotine abstinence compared to exclusive CC and exclusive EC users.” Indeed, the complete analysis of the new paper reveals that it is consistent with this review.
They also ignored two systematic reviews of the health effects of dual use, one of 49 studies as of April 2021 that concluded “Existing studies indicate that dual use is at least as, or probably even more, harmful than [just smoking]” and another of 93 estimates from 81 papers as of October 2023 that concluded, “Pooled odds ratios for dual use versus cigarettes were increased for all [analyzed disease] outcomes (range, 1.20 to 1.41).”
Thus, because dual use is more dangerous than smoking and providing e-cigarettes for smoking cessation creates many more dual users than quitters, providing smokers e-cigarettes actually increases risk. Rather than being “reassuring,” a complete analysis of Hajek’s data is evidence against using e-cigarettes as a cessation aid.
A failure of peer review?
I’m not terribly surprised that the Hajek group ignored these papers; e-cigarette advocates have a habit of ignoring inconvenient evidence. It is disappointing, however, that the reviewers and editors an Nicotine and Tobacco Research, which published the new paper did not catch these problems in peer review and at least require the authors to remedy these problems and modify their conclusions accordingly.
Here is the abstract:
Introduction: Limited data exist on how to use e-cigarettes (EC) to optimize smoking cessation.
Methods: We examined associations between patterns of EC use and outcomes at 1 year in a large trial (N = 886) comparing nicotine replacement therapy (NRT) and EC.
Results: Use of tobacco flavor was limited and associated with a lower smoking cessation rate compared to other flavors (relative risk; RR = 0.56, 95% CI = 0.35 to 0.89). EC users reduced nicotine strength over time. Abstainers using EC reported lower urges to smoke than abstainers using NRT at both weeks 1 (b = -0.25, 95% CI = -0.45 to -0.04) and 4 (b = -0.37, 95% CI = -0.58 to -0.16). Participants using both cigarettes and EC (dual users) at week 1 were more likely to stop smoking at week 4 than exclusive smokers (RR = 4.45, 95% CI = 1.96 to 10.10). Dual users at 4 weeks and 6 months were also more likely to achieve validated 50% reduction in smoke intake at 1 year (RR = 2.37, 95% CI = 1.36 to 4.11 and RR = 4.56, 95% CI = 2.71 to 7.66, respectively).
Conclusions: Non-tobacco flavors were preferred and may be also more effective. Urges to smoke were lower in EC users than in users of NRT. Dual use was associated with a reduction in smoking and quitting smoking later on.
Implications: Clinicians advising smokers wanting to use EC as a quitting aid can consider recommending non-tobacco flavors; explaining that EC reduce urges to smoke more than combination NRT; and reassuring those worried about dual use that such use is associated with reduced smoking and a higher chance of stopping smoking altogether later on.
The full citation is: Pesola F, Myers Smith K, Przulj D, Ladmore D, Phillips-Waller A, McRobbie H, Hajek P. Patterns of e-Cigarette Use and Smoking Cessation Outcomes: Secondary Analysis of a Large Randomised Controlled Trial to Inform Clinical Advice. Nicotine Tob Res. 2025 Dec 10:ntaf240. doi: 10.1093/ntr/ntaf240. Epub ahead of print. PMID: 41368708. It is available here.
Stanton Glantz blog 
The new editor in chief is a fanatical advocate of “harm reduction”.
Reiner
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