To better understand the processing of e-cigarette prevention messages, we conducted a content analysis of 1,968 participants' open-ended responses to one of four messages, which focused on industry manipulation (Big tobacco), financial and psychological cost of vaping (Can't afford), harmful chemicals in e-cigarettes (Formaldehyde), or uncertainty about the ingredients of e-liquids (Top secret). Health Belief Model (HBM) and perceived message effectiveness (PME) constructs were coded and the frequency of each variable was compared across message conditions. Among the HBM constructs, perceived health threat had the most mentions overall (38.8%). Self-efficacy of staying away from vaping had the fewest mentions across all messages (0.56%). For PME, participants more frequently mentioned message perceptions (15.75% positive message perceptions, 8.38% negative) than effect perceptions (3.46% positive effect perceptions, 1.37% negative). Big tobacco received the highest number of mentions for positive message perceptions and Formaldehyde received the highest number of mentions for positive effect perceptions. Future anti-vaping messages are recommended to address the efficacy element and to combine different themes to communicate harms of e-cigarettes.