Applying a mixed-methods approach to evaluate and tailor electronic cigarette pictorial health warning labels for young adults in the United States

BACKGROUND: The use of electronic nicotine delivery systems (ENDS) has risen significantly among US young adults, mainly driven by marketing, product design, and addictive nicotine. Pictorial warning labels (PWLs) effectively inform consumers about the risks associated with ENDS use, yet young users were rarely involved in their development. A set of 24 PWLs, categorized into three themes, was developed by a panel of international tobacco control experts via a Delphi study: ENDS toxicity, health risks, and specific harm. In this study, we involved young ENDS users through a mixed-methods approach, including a rating survey to identify the most effective warnings and focus group discussions to gather their feedback on the PWLs design, content, and needed improvements. METHODS: We conducted 22 HIPAA-compliant Zoom focus groups with 61 ENDS users (57% females, aged 21-29). Guided by the Message Impact Framework, participants completed an anonymous rating survey of the PWLs to assess attention, reactions, and perceived effectiveness, followed by in-depth discussions of each PWL. Descriptive statistical analysis was conducted for the rating survey. Focus group sessions were audio-recorded, transcribed, and thematically analyzed. RESULTS: Survey results showed toxicity-focused PWLs outperformed those on health effects and specific harm across most outcomes. Focus group results showed warnings depicting human suffering were most impactful. Relevance to participants (e.g., pregnancy, health experiences) emerged as influential factors shaping perceptions of warning effectiveness. Metaphorical images were often perceived as confusing or less believable, thereby diminishing their persuasive potential. Participants recommended applying clear, simple visual and verbal explanations. CONCLUSIONS: This study identified promising PWLs for young adult ENDS users and provides practical guidance to strengthen warning design and regulatory efforts. Warnings featuring clear, literal imagery and human health consequences elicited greater fear, perceived severity, and motivation to reconsider ENDS use, whereas metaphor-based images were often viewed as less credible or confusing. The convergence of quantitative and qualitative findings underscores the importance of targeting emotional and cognitive message responses to enhance warning effectiveness. Since personal relevance varies per individual, using a rotating, diverse portfolio of ENDS warnings targeting different health risks likely improves subgroup resonance and maximizes population impact.