Project Summary Black college students who attend Predominately White Institutions (PWIs) in the United States (US) are disproportionately exposed to both explicit and subtle racial discrimination, which is associated with substance use, misuse, and substance use-related consequences. However, much of the existing research on racial discrimination and substance use in Black college students has focused on alcohol, using retrospective self- report and cross-sectional surveys. The lack of in vivo prospective data prevents us from understanding how Black college students’ substance use behaviors fluctuate in near real-time subsequent to racial discrimination experienced in near real-time. Examining racial discrimination and substance use at the momentary level is especially important for Black college students at PWIs who report facing unique race-related stressors compounded by stressors generally associated with the college environment (e.g., increased responsibilities, academic pressures) that are also known risk factors for substance use. In addition, US colleges are witnessing national increases in nicotine, marijuana, and other drug use. Therefore, examining racial discrimination as a risk factor for the use of multiple substances warrants greater empirical attention. The proposed study aims to fill these knowledge gaps by leveraging ecological momentary assessment, a repeated collection of real-time data, and advanced statistical analyses (e.g., multilevel modeling) to investigate how racial discrimination “gets under the skin” to increase Black college students’ substance use risk. Aim 1 addresses concurrent and lagged effects at the between-person and within-person levels: (1) Do Black college students who report higher experiences of racial discrimination on average (i.e., across time) report higher levels of substance use (between-person effects)? (2) Do Black college students report substance use more on days when they report more racial discrimination than usual (i.e., higher than their personal mean) (within- person effects)? In response to national priorities that call for empirical investigations of mechanisms linking racism to substance use and misuse in marginalized groups, this study draws on the Psychological Mediation Framework to generate knowledge about the indirect effect of racial discrimination on substance use through affective, social, and cognitive processes (Aim 2). This study represents an unprecedented opportunity to collect repeated real-time data on racial discrimination, substance use (alcohol, nicotine, marijuana, other drugs), and substance use patterns (e.g., types of use, quantity of use, co-use) among a subgroup of Black Americans in a developmental period known to be associated with high-risk substance use. In line with NIDA’s Racial Equity Initiative and 2022-2026 Strategic Plan, findings from this study will help identify specific mechanisms as intervention targets to address substance use disparities relat...