Exploring Historical Trauma, Racial Discrimination, PTSD, and Substance Use Among Black Young Adults - Project Summary Overdose deaths are exponentially rising for Black individuals compared to White, where over 50% of overdose fatalities are associated with polysubstance use. Polysubstance use is a common method of use among Black young adults, placing them at a greater level of risk for mortality. Racism is a social determinant of substance use for Black populations and may in part explain some of the observed disparities. Racism is commonly operationalized and measured as racial discrimination. Racial discrimination measured at its various levels (i.e., institutional (overt), interpersonal (covert), and internalized) have each been positively associated with increased substance use. The impact of racial discrimination has been narrowly defined, only accounting for present-day experiences, and omits the influence of intergenerational, historical influences of racism, or historical trauma. Historical trauma is conceptualized as losses due to racial and ethnic cleansing, oppression, and colonization and has been linked to increased substance use among Indigenous youth. Historical trauma may also serve as an explanation for increased polysubstance use in Black young adults by understanding the increased vulnerability to racist-related events both present and past. Beyond the strong evidence of the co- occurrence of posttraumatic stress disorder (PTSD) and substance use disorder (SUD), there is also evidence that racism-based stressors, like racial discrimination, are also associated with elevated PTSD symptoms among Black young adults, but little is known about the interplay with historical trauma. This cross-sectional, quantitative study is unique and novel, as it aims to measure the impact of racism- related experiences (major discriminatory events (overt), racial microaggressions (covert), internalized racism, and historical trauma) more comprehensively on PTSD symptoms and polysubstance use among Black young adults (N = 300), while also psychometrically testing the properties of the adapted Historical Loss Scale. It is hypothesized that increases in present-day racism-based experiences will be positively related to increased polysubstance use through PTSD symptoms. Second, the association between present-day racial discrimination and PTSD symptoms will be moderated by levels of historical trauma. Ultimately, it is hypothesized that the subjective response to racism-based events may be more pronounced among participants who endorse greater experiences of historical trauma. The psychometric evaluation will be conducted using confirmatory factor analysis and testing the associations between historical trauma and psychological symptoms (complex trauma symptoms, PTSD symptoms, rumination, grief, and anger) to measure construct reliability. This study revolutionizes the conceptualization of racism as a social determinant of substance use by including both present-day and historical influences, while focusing on a specific form of substance use, polysubstance use, that increases risk for fatal overdose. Results from this project can help inform prevention and intervention efforts targeting at reducing polysubstance use from a culturally sensitive lens.