Reporting Harm Reduction Outcomes in E-cigarette Research: A Systematic Review of Randomized Control Trials

The efficacy of e-cigarettes as a smoking cessation or harm reduction aid is hotly contested in the scientific literature, and the resolution to this question is hampered by insufficient reporting standards and methodological heterogeneity. Typically, smoking cessation aids are used for short periods of time, and the subsequent cessation outcomes of interest are cigarette cessation, reduction, and failure. However, sustained e-cigarette use is common and can result in additional cessation outcomes of replacement (sustained e-cigarette use after cigarette cessation), reduction with dual use, and failure with dual use. This last category results in smokers who increase the harms they are exposed to by adding a new habit with independent risks. The degree to which people become replacers or dual users is not well understood. The aim of this current review is to investigate the role of e-cigarettes in cigarette cessation, with a special focus on the behavioral outcomes of sustained e-cigarette use (i.e., dual users and replacers). In a systematic review of randomized control trials, we found that while behavioral outcomes of cigarette use were well-reported, replacement and the two categories of dual use are rarely reported. Only one study reported all six possible outcomes, and only two additional studies reported dual use at all. Continued cigarette smoking (i.e. reduction or failure) were by far the most likely outcomes. Without tracking continued e-cigarette use, it is impossible to determine whether e-cigarettes decreased or increased harm. These behavioral outcomes are obscured in the data when they are collapsed into cessation categories incongruent with the specifics of e-cigarette use. We provide guidelines for reporting these unique outcomes and present some discussion of the disparate methodology across these nine studies.