Abstract
BACKGROUND: The emergence of electronic nicotine delivery systems (ENDS, or "e-cigarettes") has resulted in nicotine and tobacco scientists committing increased resources to studying these products. Despite this surge of research on various topics related to e-cigarettes, it is important to characterize the evolving e-cigarette research landscape as a way to identify important future research directions. The purpose of this review was to broadly categorize published scholarly work on e-cigarettes using a structured, multi-level coding scheme. METHODS: A systematic literature search was conducted to collect articles on e-cigarettes that were published in peer-reviewed journals from 2006 through 2014. Studies were classified through 3 coding waves. Articles were first divided into research reports, literature reviews and opinions/editorials. Research reports were further categorized to determine the proportion of these studies using human participants. Finally, human studies were classified based on their methodologies: descriptive, predictive, explanatory, and intervention. RESULTS: Research reports (n=224) and opinions/editorials (n=248) were published at similar rates during this time period. All types of articles showed exponential rates of increase in more recent years. 76.4% of human research studies were descriptive in nature, with very little research employing experimental (6.8%) or intervention-based methodologies (5.4%). CONCLUSIONS: This review reinforces the idea that e-cigarettes are a disruptive technology exerting substantial influence on nicotine and tobacco science. This review also suggests that opinions on e-cigarettes may be outpacing our scientific understanding of these devices. Our findings highlight the need for more e-cigarette research involving experimental, intervention, and longitudinal designs.