US adolescents' response to nicotine warning labels in influencer e-cigarette marketing social media posts: a survey-based randomised between-subject experiment.

Background: E-cigarette promotional posts with misleading nicotine warning labels on social media may lower adolescents' risk perceptions of e-cigarettes. A between-subject experiment assessed effects of influencers' e-cigarette promotional posts with different nicotine warning labels on adolescents' e-cigarette harm perceptions, susceptibility to e-cigarette use and perceptions of influencer credibility.

Methods: In 2022, adolescents (N=1864, M_age=17 (SD=0.6)) were randomised to view six images and videos featuring influencers promoting e-cigarettes in one of five experimental conditions: two conditions with a 'tobacco-free nicotine' warning label (placed on an e-cigarette in the post or at the top of the post), two conditions with the US Food and Drug Administration (FDA) nicotine warning label (on an e-cigarette in the post or at the top of the post (control)) and one no-label condition. Participants rated influencers' credibility (eg, honesty). Harm perceptions of, and susceptibility to use, e-cigarettes were then assessed.

Results: Participants who viewed posts with the FDA warning label at the top of the post perceived influencers as more honest, trustworthy and informed than in all the other conditions. E-cigarette never-users who viewed posts with a 'tobacco-free nicotine' warning label pictured on an e-cigarette (compared with the FDA label at the top of a post) were more likely to report susceptibility to e-cigarette use (adjusted OR 1.79, 95% CI 1.17 to 2.73).

Conclusions: Alterations of the required nicotine warning labels can make them less effective in deterring e-cigarette use behaviour. Tobacco control authorities could increase enforcement of the FDA-required nicotine warning labels and harness influencers for antitobacco messaging.