Dual use is not an intermediate condition on the way from cigarettes to “switching completely” or quitting

Discussion of potential harm reduction associated with the use of e-cigarettes assumes that smokers will “switch completely” from cigarettes to e-cigarettes or stop both tobacco products. Advocates of this view, including the US FDA, recognize and accept that this process may include a period of dual use in which smokers use both products. Now Josef Hamoud and colleagues have examined trajectories of both product users over time among people who are dual users and found that the assumption that dual use is a transition of e-cigarette only use or tobacco abstinence is wrong.

Specifically, their new paper A Systematic Review Investigating the Impact of Dual Use of E-Cigarettes and Conventional Cigarettes on Smoking Cessation, which quantified use status transitions of the same people over time around 6 (graphic above), 12, 24 and 48 months between dual (DU), exclusive e-cigarette (EC), exclusive cigarette (CC), and non-use (NU). They found that dual use is very common and cannot merely be considered a short-term transitional status. Specifically, they concluded, “Current evidence suggests that DU is not a first step toward smoking cessation, with most DUs continuing cigarette consumption either through persistent DU or exclusive CC smoking. Relatively fewer dual users transitioned into complete nicotine abstinence compared to exclusive CC and exclusive EC users.“

This is an important finding because dual use is riskier than cigarette smoking or e-cigarette use alone. While most randomized controlled trials of e-cigarettes as medical cessation treatments did not report dual use among patients who were “treated” with e-cigarettes did nor report dual use as an outcome, those that did found that more smokers randomized to receive e-cigarettes became dual users that switched completely. Dual use is also common among people using e-cigarettes as consumer products: the 2020 Eurobarometer survey reported that 59% of European e-cigarette users also smoke conventional cigarettes.

The bottom line: “our results suggest that in naturalistic observations dual users are less likely than exclusive CC smokers or exclusive EC users to quit smoking, falling in line with evidence implying that DU use might reinforce nicotine dependence.”

As a result dual use should be considered an adverse outcome in clinical trials and evidence for harm enhancement in population studies.

Here is the abstract:

Background. Dual use (DU) of conventional cigarettes (CC) and e-cigarettes (EC) has emerged as a common pattern among youth and adult populations. This review aims to investigate whether dual use can promote smoking cessation.

Methods. A systematic search was conducted in accordance with PRISMA guidelines, and all longitudinal studies reporting transitions between DU, exclusive e-cigarette use and exclusive conventional cigarette use were included. Two independent reviewers screened and read all records. Use status transitions among dual users were compared to transitions among exclusive e-cigarette users and exclusive CC smokers.

Results. Forty-six records (sixteen original studies) were identified. Of sixteen included studies, eight could be pooled for meta-analysis. The studies showed great heterogeneity, and many presented moderate to high risks of bias. Most dual users who changed state transitioned to cigarette smoking. Baseline dual users were less likely to report a transition into complete abstinence compared to exclusive CC smokers and exclusive EC users. About one-fifth of dual users remained in the same use status after >16–24 months, exposing them to DU for a prolonged time. After >24–48 months, 8% of DU maintained DU.

Conclusion. Current evidence suggests that DU is not a first step toward smoking cessation, with most DUs continuing cigarette consumption either through persistent DU or exclusive CC smoking. Relatively fewer dual users transitioned into complete nicotine abstinence compared to exclusive CC and exclusive EC users. The concerns raised about limitations of current evidence highlight the need for more research focussed on use status transitions among dual users.

The full citation is: Hamoud J, Hanewinkel R, Andreas S, et al. A Systematic Review Investigating the Impact of Dual Use of E-Cigarettes and Conventional Cigarettes on Smoking Cessation. ERJ Open Res 2024; in press (https://doi.org/10.1183/23120541.00902-2024). It is available here.