Indiana University-Purdue University Indianapolis (IUPUI) / AIM People with marginalized sexual orientations experience mental health and substance use problems at a higher rate compared to heterosexuals. Experiences of discrimination have been identified as a significant factor in explaining such disparities, and a growing body of literature has developed seeking to explore the contexts in which discrimination occurs. However, one context that is understudied is the online environment. Based on Meyer’s (2003) Minority Stress Model (MSM), it is postulated that specific proximal group-specific processes mediate the relationship between discrimination and health outcomes, with other social factors providing protective effects. However, research is sparse empirically investigating different mechanisms, consequences, and potential modifying factors for sexual minority young adults experiencing online heterosexist discrimination (OHD). Thus, the current study aims to explore experiences of OHD among young adults. METHODS Using the MSM as a guiding framework, the study examined proximal factors of internalized heterosexism, online concealment, and rejection sensitivity as mechanisms underlying the effect of OHD on health outcomes and online social support as a moderating factor. 383 young adults (18-35) with marginalized sexual orientations were recruited from an introductory psychology subject pool, two online crowdsourcing platforms (Prolific, MTurk), and the community. They completed measures of OHD, online social support, online concealment, rejection sensitivity, internalized heterosexism, psychological distress, and substance use. RESULTS Path analyses in Mplus revealed that two proximal stressors (rejection sensitivity, sexual orientation concealment) were positively related to psychological distress as a result of OHD. Sexual orientation concealment was associated with increased risk for cannabis use due to OHD. Online social support from LGBTQ+ peers did not buffer these relationships. CONCLUSION The MSM is a viable guiding framework in exploring OHD. Rejection sensitivity and online sexual orientation concealment are important constructs to consider for future research and may be ideal treatment targets for individuals experiencing psychological distress or engaging in cannabis use due to OHD.