PROJECT SUMMARY/ABSTRACT Trans and nonbinary (TNB) individuals experience mental and physical health disparities compared to cisgender peers, such as higher rates of depression and anxiety, increased risk for suicide, substance use and poor physical health. These disparities are associated with internalized anti-TNB stigma, discriminatory interpersonal encounters, and systemic and institutional barriers to accessing necessary social, financial, educational, and health resources, and are exacerbated among TNB People of Color (POC) and those with fewer resources. Research across populations indicates that social support has multiple beneficial effects, including mitigating adverse mental health outcomes and promoting well-being. There is a critical need to identify the most effective types of social support for all TNB individuals, particularly those facing the greatest barriers to societal institutions and resources. Using community-engaged and innovative approaches to rigorously over-sample TNB POC, we will identify within-group differences in the specific forms social support that promote health and mitigate risk across TNB communities. Data from a total of 1299 TNB individuals diverse in race and ethnicity will be collected across several studies using multiple methods (e.g., qualitative interviews and focus groups; ecological momentary assessment, longitudinal survey research) to develop and validate a multi-faceted social support measure and test its function within an intersectional minority stress theory-derived longitudinal model. The overall objective of this proposed research is to take the critical step toward this long-term goal by advancing knowledge of social support as a mechanism by which to reduce anxiety, depression, and suicide risk, promote well-being among TNB individuals, and to develop the measurement tools necessary to investigate their impact on mental health and well-being over time and in context. This project includes the following three specific aims: (1) Use community engaged approaches, we will collect data to increase in-depth understanding of how TNB individuals experience and use social support to address adverse mental health concerns, (2) Develop and validate a multifaceted measure of social support for TNB individuals for use in research and clinical settings, and (3) Longitudinally assess the effects of social support in a minority stress model of TNB mental health. Data ( focus groups, individual interviews with community leaders, and daily diary social contacts logs) will be collected to inform essential domains of social support for TNB people [Aim 1]. This information will be integrated into the development of a multifaceted social support measure and cutting-edge network-based psychometric analyses will be used to validate the measure with a sample of 1000 TNB participants [Aim 2]. Longitudinal survey data from 1000 TNB adults at three time points to test the strength of direct and moderating effects of various dimensions of social support on mental health (e.g., depression, anxiety, suicidality) and mitigating mental health risk associated with anti-TNB stigma [Aim 3].

PROJECT NARRATIVE Social support has multiple beneficial effects that mitigate adverse mental health outcomes and promote well- being across all populations. Understanding how to optimize social support for transgender and nonbinary (TNB) populations, specifically those experiencing multiple forms of marginalization, could meaningfully reduce TNB mental health disparities, specifically depression, anxiety, and suicide risk. Using an intersectional framework and a community-engaged approaches, this project will identify the most crucial aspects of social support for TNB populations for reducing adverse mental health outcomes, and to develop the measurement tools necessary to support future prevention and intervention strategies that can build and leverage social support to improve TNB mental health.