PROJECT SUMMARY: P4 P4: Social Media Influences on Engagement and Susceptibility to Non-Combustible Product Use (Co- leaders, Unger/Allem) P4 determines how social media depictions of ONPs and e-cigarettes with varying features are engaged with by the public and influence youth use susceptibility on modern platforms frequented by AYAs (e.g., Tiktok) . To accomplish this, P4 will: a) collect publicly-available social media posts depicting ONPs and e-cigarettes and conduct deep content analysis to examine if posts with certain features (e.g., flavors, post from social media ‘influencer’) receive more likes and shares; b) to test effects of exposure to social media posts depicting e- cigarette and ONPs in varying flavors and designs on youth susceptibility. Aim 1 is to analyze video posts from TikTok, Instagram, Twitter, and emerging social media platforms to examine how ONPs and e-cigarettes are portrayed on modern social media and engaged with by the public. Using a multi-method strategy, we will code social media postings according to the types of products mentioned, flavors, stealth use, and other potentially youth-appealing characteristics. Hypothesis (H)1: Posts that reference concept flavors with ambiguous names (e.g., sunset, lava); concealability and stealth use; health benefits; lack of warning labels; convenience; combustible cigarette cessation; use social media influencers; and/or use young-looking models will receive greater degrees of engagement (e.g., likes, shares, retweets) compared to posts without these characteristics. Aim 2 is to determine whether exposure to social media content from Aim 1 depicting concept-flavored e- cigarettes and ONPs affect youth use susceptibility. We will recruit high school students (n=1,500 per year) into experiments. Using digital tablets, youth view social media posts mentioning e-cigarettes and ONPs that vary on the following characteristics: 1) flavor (ambiguous concept flavor [e.g., sunset] vs. explicit characterizing flavor [e.g., strawberry] vs. posts without flavor mentions); 2) mentions of concealability and stealth use (yes/no). Post- exposure self-reported perceptions and susceptibility to using the product depicted in the posting will be measured. H2a: Susceptibility to using the ONP or e-cigarettes will be higher among youth assigned to view social media posts with concept or characterizing flavors and/or references to stealth use. H2b: The relation of social media post characteristics with susceptibility to use will be mediated by product perceptions. Implications for regulation: If posts with concept flavor descriptors, references to stealth use, or other features increase engagement and susceptibility to using ONPs or e-cigarettes, exposure to newly-marketed products on modern social media platforms could promote AYA use. We will provide the FDA with evidence to inform marketing restrictions on the terminology, models, and overall content that companies can use in promotional social me...