Abstract
Health warnings for e-cigarettes are a promising and novel tobacco control intervention for reducing e-cigarette use. We developed a new protocol for evaluating e-cigarette warnings by placing them on users' own devices to reflect real-world exposure. Study 1 participants were a national convenience sample of 606 U.S. adult e-cigarette users surveyed online in March 2017. Most Study 1 participants were willing to have their e-cigarette devices (87%) and refills (83%) labeled. Study 2 participants were a convenience sample of 22 adult e-cigarette users recruited in California, United States in April 2017. We applied the U.S. Food and Drug Administration's proposed e-cigarette warning to users' own devices and refills. Most Study 2 participants (81%) reported using e-cigarette devices with our warning labels at least 90% of the time during the study. Nearly all (95%) said they would participate in the study again, and 100% would recommend the study to a friend. Conversations about e-cigarette harms, conversations about quitting e-cigarettes, and intentions to quit using e-cigarettes increased during the study (all p < 0.05). These studies show that our naturalistic labeling protocol was feasible, acceptable to participants, and had high retention over three weeks. Using the protocol can yield important evidence on the impact of e-cigarette warnings to inform tobacco warning policies.