The dual use dilemma: Is it better to have tried and failed to quit smoking with e-cigarettes or to have never tried e-cigarettes at all?

E-cigarettes are an effective way to stop smoking but there is disagreement regarding their use as treatment. One concern is that recommending e-cigarettes for adults who smoke (AWS) could result in sustained dual use of both products among those who fail to quit smoking. Given most quit attempts end in failure, it is important to understand the likelihood of developing dual use and its consequences when considering e-cigarettes for AWS. We describe variability in dual use within a behavioral economics framework, including literature which addresses the likelihood that trying to quit smoking with e-cigarettes will lead to established dual use as well as the impact that dual use has on smoking heaviness and smoking cessation. Limited evidence suggests that a meaningful minority of AWS who initiate e-cigarettes with support to quit smoking establish dual use. Compared to exclusive smoking, dual use appears to be associated with an overall reduction in smoking and an increase in the likelihood of cessation. However, outcomes appear to vary based on substitutive versus complementary use patterns, with the potential for dual use to lead to sustained or increased smoking for a small proportion of AWS who initiate e-cigarettes. Compared to exclusive smoking, developing dual use is likely associated with reduced smoking for the majority of AWS, providing further support for including e-cigarettes as a smoking cessation treatment option. Future prospective and controlled research is needed to explore predictors of developing substitutive versus complementary patterns of dual use and subsequent smoking cessation.