Parents will receive the alcohol and social media PBI and adolescents will receive a brief alcohol and social media PFI based on our previous work. The PFI will use data from the adolescent baseline survey to create personalized alcohol and social media intervention feedback including normative comparisons to peers and summaries of risk behaviors. Adolescents will be encouraged to complete the PFI in one sitting but can revisit as many times as they like.

The alcohol and social media PBI will be based on our pilot work (R34AA026332) and updated/tailored based on Aim 1 FGs. The PBI will be delivered via a web-based format such that parents will be sent an email and a text message containing a URL to the alcohol and social media PBI website along with guidelines for working through the modules (see below for overview of modules). The website will allow parents to navigate through the modules at their own pace/sequence. Each module will have interactive elements including animations, infographics, and videos to highlight key content. Parents will be sent one text message per week encouraging them to use the website.

Parents will be emailed a link to the Power of Parents Handbook, which is a 52- page static PBI handbook (Turrisi et al., 2001, 2009, 2013) housed on the MADD website offered in English and Spanish. The alcohol PBI instructs parents to use an empathic communication style while providing information about alcohol use.

Parents will receive the alcohol and social media PBI and adolescents will receive a brief alcohol and social media PFI based on our previous work (PI: Litt, R21AA024163; Litt et al., 2023; Lewis et al., 2019; Larimer et al., 2021, 2023). The PFI will use data from the adolescent baseline survey to create personalized alcohol and social media intervention feedback including normative comparisons to peers and summaries of risk behaviors. Adolescents will be encouraged to complete the PFI in one sitting but can revisit as many times as they like.

The Drinking Refusal Self-Efficacy Questionnaire will assess beliefs in one's ability to resist alcohol (Young et al., 2007; α = .96). Responses range from 1 (I am very sure I would drink) to 6 (I am sure I would not drink) with higher scores indicating greater drinking refusal self-efficacy.

Alcohol-related social media communication between parents and adolescents will be assessed using the "Alcohol-related Social Media Communication Scale, which is adapted from Turrisi et al., 2000; α = .96). Participants will indicate whether they spoke about a range of topics (yes/no) in the past month with higher scores indicating greater alcohol-related social media communication.

The willingness measure will assess adolescent willingness to drink in certain scenarios (α = .85; Gerrard et al., 2008) using a response rage of 0 (not at all willing) to 4 (extremely willing). Higher scores indicate greater willingness to use alcohol.

Alcohol initiation for those who abstain at baseline will be calculated as time-to-event from baseline date to participants' reported date of first use using timeline follow-back methods (Sobell & Sobell, 1992) and reporting the approximate date they first used alcohol, an approach used in our current work (R01AA025611).