Project Summary/Abstract Long Term Objectives The goal of the proposed project is to identify proximal motivational risk factors for simultaneous alcohol and marijuana (SAM) use in daily life. The applicant’s long-term career objective is to establish a program of research integrating daily-life approaches with complementary methodologies to characterize the factors contributing to daily-life engagement in substance use. Specific Aims The project will utilize alcohol administration and ecological momentary assessment (EMA) methods to characterize various motivational processes that may lead to SAM use by testing 1) whether marijuana craving and expectancies differ as a function of alcohol intoxication in the laboratory, 2) how well marijuana self-reports during laboratory alcohol intoxication map onto marijuana self-reports during daily life drinking episodes, and 3) various premises of the motivational model of substance use, as applied to SAM use in daily life. Method Participants (N = 80) who report frequent SAM use will be recruited for a 14-day EMA study during which they will report 5 times per day on their momentary affect, craving, motives, substance use, and subjective effects of use, with additional event-based and follow-up reports to more densely sample substance use episodes. A subset (N = 40) of participants will also, prior to the EMA phase, complete a laboratory alcohol administration procedure during which they will report on subjective alcohol effects and MJ craving and expectancies at several time-points across the BAC curve. Significance The proposed project integrates laboratory alcohol administration with daily-life assessments to provide a more detailed characterization of the proximal risk factors for SAM use than has been done thus far. Individuals who engage in SAM use experience negative consequences above and beyond those associated with the use of alcohol or marijuana alone. Findings from the proposed project may inform potential targets for intervention.