The emergency department (ED) is on the front lines of the overdose epidemic, treating an increasing number of people with opioid use disorder (OUD). In the year after an ED visit for an opioid overdose, more than one in twenty patients will die. Each visit represents a crucial opportunity to link patients to harm reduction and treatment services, there are significant gaps in service provision across Rhode Island EDs with less than half receiving take home naloxone, less than one in three receiving behavioral counseling, and one in five linked to addiction treatment. To improve provision of lifesaving harm reduction and treatment services in the ED, we launched a multidisciplinary ED community health worker (CHW)-peer recovery specialist program, the Substance Misuse Assistance Response Team (SMART), at a large, academic, urban medical center which cares for the majority of opioid overdose patients in Rhode Island. Drawing from models of existing peer recovery specialist, CHW, and health promotion advocate programs, SMART is a novel ED-based program that provides people with a substance-use related ED visit individualized support, short term case management, navigation to substance use treatment, harm reduction services, and social services both in and out of the ED. In recent years there has been a proliferation of ED peer recovery programs, but little is known about their effectiveness and implementation potential. In this study, we will conduct a hybrid type 1 effectiveness-implementation study to assess the effectiveness of an ED CHW-peer recovery specialist program and identify barriers and facilitators of successful implementation in the acute care setting. In this mixed methods study, we will use hospital and state administrative databases, surveys, and qualitative interviews to evaluate the effectiveness of the ED CHW/peer recovery program on a range of patient and program outcomes, including provision of harm reduction and treatment services and changes in acute care utilization, repeat overdose, and mortality among people receiving SMART. Consistent with best practices in hybrid type 1 trials, we will simultaneously gather data on inner and external factors influencing implementation potential in the acute care setting. This study will provide pilot effectiveness data for a subsequent R01 application for a multilevel, comprehensive implementation study to identify implementation strategies for program enhancement, dissemination, and sustainability.