The Impact of Health Warnings in e-Cigarette Content on Instagram on Adults' e-Cigarette Cognitions: Online Between-Subjects Experiment Study.

Background: e-Cigarette use is a growing public health concern, with e-cigarettes being marketed by social media influencers on Instagram. Influencers promote e-cigarettes using misleading relative harm claims, portraying them as safer than regular cigarettes while overstating benefits and selectively omitting information on the harms. To counter this, the US Federal Drug Administration requires influencers to include a nicotine warning label in their sponsored posts, similar to the ones used on e-cigarette packages. However, research on their effectiveness remains limited, leaving questions about when, how, and for whom these warnings work.

Objective: This study examined how (1) relative harm claims and (2) health warnings in influencers' sponsored e-cigarette content influence health outcome expectations and intentions to use e-cigarettes. In addition, we investigated whether user status (ie, smoking cigarettes or vaping e-cigarettes vs nonuse) moderates these effects.

Methods: Participants (n=597 age: mean 40.84, SD 11.93 years) were recruited through a survey company using a quote-based sample of German adults aged between 18 and 60 years, stratified by age, gender, and education. We conducted a preregistered 2 (relative harm claim: absent or present) × 2 (health warning: absent or present) between-subjects experiment. Participants viewed Instagram profiles of 2 influencers and separate posts including sponsored e-cigarette content. Relative harm claims in sponsored e-cigarette posts were manipulated by adding captions stating that e-cigarettes are healthier than cigarettes, with misleading information about why this could be the case. Neutral captions described product features in the relative harm claim absent condition. Health warnings appeared as a black text on a white background containing a nicotine warning statement. Participants then reported measures on attitudes, outcome expectations, intentions, and personal e-cigarette and cigarette use. Multivariate analysis of covariance and moderated mediation analyses were used to test the direct and interaction effects of misleading relative harm claims and health warnings.

Results: Misleading relative harm claims significantly influenced health outcome expectations (F=5.88, P=.02, η=0.011), with participants exposed to harm claims about e-cigarettes reporting lower negative outcomes (mean 5.25, SD 0.09) compared to those who did not (mean 5.58, SD 0.10). Health warnings had no statistical significant effect on attitudes, health outcome expectations, or intentions. No interaction effect between health warnings and relative harm claims was observed. Overall user status (ie, cigarette or e-cigarette use vs nonuse) did not moderate these effects.

Conclusions: Health warnings as mandated by the Federal Drug Administration were ineffective in reducing the persuasive impact of influencers' appealing e-cigarette content, regardless of an individual's own experiences with cigarettes or e-cigarettes. Policy makers should consider tailoring warnings that address audience-specific consequences to make them more effective. In addition, media literacy interventions are essential to counter misleading relative harm claims and appealing influencers' e-cigarette content.