ABSTRACT: PROJECT 4 Smoking prevention campaigns are an effective tool for reducing adolescent and young adult cigarette smoking. However, the science of vaping prevention campaigns is just beginning to emerge. Vaping prevention video ads contain a large number of different objective ad features, and we currently know little about which ad features are most impactful for adolescents and young adults. We also know little about whether impactful ad features differ for lesbian, gay, and bisexual (LGB) adolescents and young adults who are more likely to vape than their peers. The primary goal of our project is to characterize the objective features of vaping prevention video ads to determine which ad features best predict perceived message effectiveness and most reduce susceptibility to vaping. Our work also explores whether impactful ads and ad features differ by sexual orientation, as well as an examination of unintended consequences of vaping prevention ads (e.g., encouraging cigarette smoking). For Aim 1, we will characterize the objective features of hundreds of vaping prevention video ads from our Vaping Prevention Resource (VPR) – the largest open access archive of vaping prevention messages in the country – and other sources. For Aim 2, we will identify which features of video ads predict perceived message effectiveness and unintended effects using an online experiment with 3,000 adolescents and young adults (ages 13-20, oversampling LGB participants) who are at-risk of vaping or currently vape. Based on the results, we will select 5 ads with promising features and 5 ads without promising features for the Aim 3 randomized controlled trial (RCT). For Aim 3, we will evaluate the ability of vaping prevention video ads with features found to be most promising in Aim 2 to reduce susceptibility to vaping. We will recruit 1,200 adolescents and young adults (ages 13-20, oversampling LGB participants) who are at-risk of vaping or currently vape to participate in an RCT with 3 online study sessions over 4 weeks. We will conduct a 2-arm trial where participants are randomized to view 1) ads with promising features (intervention) or 2) ads without promising features (control). Our primary outcome is susceptibility to vaping and our secondary outcomes include vaping risk beliefs, attitudes toward vaping, and vaping behavior. We will also explore differences in ad impact by sexual orientation as well as unintended effects on cigarette smoking outcomes. Our proposal fits within the integrative theme of the UNC TCORS of building the science for effective regulation of and communication about tobacco products disproportionately used by priority populations – e-cigarettes – in the U54 proposal “Advancing Tobacco Regulatory Science to Reduce Health Disparities.” Our project is responsive to the FDA Scientific Domains of Communications (Aims 1-3) and Behavior (Aim 3) in RFA-OD-22- 004. This work will provide crucial knowledge about which features of vaping preve...