PROJECT SUMMARY/ABSTRACT Gay, bisexual, and other men who have sex with men (GBM) in the U.S. experience striking health disparities related to alcohol use and HIV. Heavy alcohol use is a significant threat to adherence to antiretrovirals (e.g., antiretroviral therapy [ART]) among GBM managing HIV. However, it is unclear if alcohol use impacts adherence to Pre-Exposure Prophylaxis (PrEP) for preventing HIV. PrEP is used by >35% of U.S. GBM and can be taken either daily or taken in sequence around a sexual event (i.e., event-driven PrEP). PrEP is a highly effective oral antiretroviral but studies have demonstrated suboptimal adherence for both PrEP regimens. Heavy alcohol use and specific beliefs related to mixing alcohol and PrEP may contribute to suboptimal adherence. For instance, >60% of GBM interested in taking PrEP falsely believe that mixing alcohol with PrEP results in a toxic combination (i.e., interactive toxicity beliefs). Like other erroneous beliefs (e.g., HIV is manmade), interactive toxicity beliefs may diffuse across the social network and, subsequently, influence adherence. The proposed study will employ an egocentric social network interview and a semi-weekly diary phase over five weeks to (1) examine associations between heavy alcohol use and PrEP adherence, and (2) to test alcohol-interactive toxicity beliefs and social network characteristics as risk factors for PrEP non-adherence. GBM (N=100) who are taking PrEP will be recruited via brick-and-mortar entities (e.g., LGBTQ+ centers and bars), local health clinics, and online advertising in Harris County, TX (i.e., the greater Houston area). At baseline, participants will complete demographics and measures of interactive toxicity beliefs. Participants will also complete an egocentric social network interview designed to obtain information on up to 20 alters (i.e., people in the social network). The interview will capture alter expression of interactive toxicity beliefs, PrEP and alcohol use, closeness, trust, overall connectedness, demographics, and norms. Participants will then complete five weeks of semi-weekly diaries that assess alcohol use, PrEP use, and HIV risk behaviors. This research can inform future PrEP-related counseling techniques and interventions aimed at correcting PrEP misconceptions and increasing adherence. The project supports the 2017-2021 strategic plan of NIAAA by advancing research in two areas. First, the project has the goal of identifying ways in which alcohol can influence the use of HIV-related medications, specifically PrEP (Goal 1C). Second, the project may enhance the public health impact of NIAAA-supported research, by focusing on how alcohol contributes to suboptimal PrEP adherence among a population with alcohol-related disparities (Goal 5). Moreover, the project contributes to research on health disparities of minority populations, which is a cross-cutting NIAAA research theme. Through this project, I will obtain the knowledge, skills, and ...