The Impact of E-Cigarette Warnings, Warning Themes and Inclusion of Relative Harm Statements on Young Adults' E-Cigarette Perceptions and Use Intentions.

Although e-cigarettes in the United States are required to carry one nicotine addiction warning, little is known about the impact of other potential e-cigarette warning themes, nor about pairing warnings with messages that communicate e-cigarettes' reduced-harm potential relative to cigarettes. We randomly assigned 876 young adults (ages 18⁻29) to view e-cigarette ads in a 3 × 2 plus control online experiment that varied by warning theme (i.e., nicotine addiction; nicotine's impact on adolescent brain development; presence of harmful chemicals) and warning type-i.e., the presence ("relative harm warning") or absence ("standard warning") of a relative harm (RH) statement in the warning label ("e-cigarettes may cause harm to health but are less harmful than cigarettes"). Warning believability, informativeness, understandability and support were high across conditions and there were no significant differences by warning theme on e-cigarette harm perceptions or use intentions nor on nicotine (mis)perceptions. Perceived warning effectiveness for discouraging youth initiation was higher for the "brain" and "chemicals" warnings compared to the addiction warning. Warnings with the included RH statement were perceived as less believable and credible and were less frequently correctly recalled. Research should continue to investigate the impact of different e-cigarette warning themes and formats with priority audiences.