Electronic cigarette use, related health outcomes and policy interventions in the USA: a call for research to fill evidence gaps

The population-level health consequences of electronic cigarette (e-cigarette) use are heavily debated. This special communication provides updated evidence and identifies knowledge gaps across domains including: (1) health-related outcomes associated with e-cigarette use; (2) initiation and use of e-cigarettes among youth and young adults; (3) concurrent use of electronic and combustible cigarettes; (4) transitions from combustible cigarette use to exclusive e-cigarette use among adults who currently smoke cigarettes and (5) existing e-cigarette-related policy interventions. Literature was searched through PubMed and Medline for systematic reviews, scoping reviews, meta-analyses and primary research articles including emerging topics not covered in reviews published between 1 January 2017 and 1 January 2024. E-cigarette use is associated with several adverse acute health outcomes; there is currently insufficient longitudinal evidence to predict chronic health outcomes. Prevalence of e-cigarette use among youth is considerable and may be associated with subsequent combustible cigarette smoking. Evidence for the health and behavioural impact of dual use of e-cigarettes and combustible cigarettes is limited by imprecise measurement of exposure. Evidence on adults completely substituting combustible cigarettes for e-cigarettes is strong in clinical trials; observational studies do not show complete substitution. Finally, the effects of e-cigarette-related policy interventions to restrict e-cigarette consumption are currently limited in scope and too short-lived to draw causal inferences. Substantial evidence gaps related to the use, associated health impacts and regulation of e-cigarettes in the USA are identified, and we suggest key areas for future research to address that are crucial for informing the public health approach to e-cigarettes.