ABSTRACT. Psychological pain, which refers to feelings of shame, guilt, humiliation, fear, angst, and dread, has emerged as an important clinical construct. The experience of psychological pain is complex; its multifactorial influences and consequences are poorly recognized, inadequately managed, and under- estimated in the general population. Additional challenges are noted in investigating pain experience in adult Black, Indigenous, and Persons of Color (BIPOC), who are more likely to be stigmatized, discriminated against, and often lack support and resources that enable them to treat their pain (i.e., psychiatric or mental health services) compared to their white counterparts. In understanding pain experience among marginalized groups, it is crucial to acknowledge that systemic inequities extend into various aspects of life, including healthcare. BIPOC people often experience sub-par healthcare due to discrimination based on race, gender and/or other sociodemographic factors. Because Emergency Care (EC) settings can be critical entry points for individuals who use substances, BIPOC people are confronted with the additional intersectional stigma that arises due to their dual characteristics as ethnic minorities as well as people who use substances. By addressing this intersectional experience, we aim to improve not only the immediate health and well- being of these marginalized patients, but also to inform broader policy and clinical guidelines surrounding substance use disorder diagnosis and treatment. In Aim 1, we first propose the use of EMA data from the parent project to measure daily experience of pain in order to test whether psychological pain is a mediator between discrimination and polysubstance use (N=270). Second, we propose the use of focus group data from the parent project to qualitatively examine the social and cultural relevance of the experience of psychological pain in the context of discrimination and polysubstance use among BIPOC adults (N~70). In Aim 3, we propose collection of an independent set of data through surveying 100 BIPOC adults being treated within the Emergency Department at Los Angeles General Medical Center (LAGMC) (N=100) to document and explore the relationships between psychological pain, healthcare discrimination, and substance use among BIPOC patients. While the parent study focuses on nicotine, alcohol, and cannabis—the three most commonly used substances in the US, Aim 3 broadens the study scope to include opioids, methamphetamines, cocaine, and benzodiazepines, as these are among the top substances linked to U.S. Emergency Department visits in 2022 and are also among the most stigmatized. Together with the parent study, this will be the first study to provide an in-depth description of the impact of discrimination on substance use behaviors in the context of daily and prolonged psychological pain among BIPOC adults. By conceptualizing pain as the mediator, future studies may develop momentary interven...