The SUPrEMe Study: Substance Use and PrEP adherence among Men who have sex with men, will examine the prevalence and pattern of substance use over time (Aim 1) and evaluate the association between substance use and PrEP adherence and persistence (Aim 2) among MSM on PrEP in Manila, Philippines. To advance these aims, I will partner with LYS and the WHO Division of Communicable Diseases in the Western Pacific (see letters of support) to conduct a secondary data analysis of the longitudinal data from Project PrEPPY, the first PrEP implementation project in the Philippines. Project PrEPPY is enrolling 200 HIV-negative MSM at high risk for acquiring HIV and provide them with daily oral PrEP (FTC/TDF) during 12 month followup, with follow up visits occurring at 1, 3, 6 and 12 months after enrollment. During follow-up visits, safety lab evaluations and physical exams, behavioral assessments, HIV risk-reduction counseling, sexually transmitted infections testing, and PrEP dispensing are conducted. Substance use patterns, including classes of substance use (e.g., methamphetamine, cocaine), and frequency of use are measured using standardized questionnaires at baseline and followup visits (Aims 1 and 2) and PrEP adherence is evaluated via pill count and adherence diary review during followup (Aim 2). Participants who decide to voluntarily discontinue PrEP are considered nonpersistent (Aim 2). Findings from this study will determine the significant of substance use as a barrier to PrEP adherence and persistence among MSM in the Philippines and ultimately help inform the development of interventions that jointly address substance use and enhance HIV prevention approaches.