Background <p>Harm reduction services are inequitably accessible and efficient among people with a history of injection drug use (PWHID), particularly among those belonging to vulnerable communities. This systematic review identifies barriers and facilitators to accessing and adhering to harm reduction services among PWHID in priority populations to gain a deeper understanding of the intersectional barriers to these services.</p> Methods <p>A systematic search was conducted using four databases (PubMed/MEDLINE, Scopus, CINAHL, and Web of Science) to locate articles examining barriers and/or facilitators associated with substance use harm reduction services among marginalized populations (e.g., racial/ethnic minorities, sexual/gender minorities, people living with HIV, veterans, etc.) in the United States. Study characteristics and key findings were extracted from studies and thematically analyzed.</p> Results <p>This review identified 25 articles that examined factors associated with initiation and adherence to harm reduction services for PWHID. The harm reduction services most identified were medications for opioid use disorders (e.g., naloxone, buprenorphine) and syringe service programs. Factors were individual-level factors (e.g., motivation, stigma, previous negative experiences), as well as service-level barriers (e.g., accessibility, distance, setting). Many studies identified participant sociodemographic characteristics (e.g., race, age, sexuality) as a facilitator or barrier, although these factors are proxies for systemic and/or structural barriers and should not necessarily be considered as intervention targets.</p> Conclusion <p>Incorporating harm reduction services as part of integrated, wraparound services in other healthcare settings may reduce barriers such as convenience, inaccessibility due to geography or transportation, stigma, and encourage service utilization as a result.</p>