Integrating HIV-related care with treatment for substance use disorder provides an opportunity to better meet the needs of people living with these conditions. People with substance use disorder are rendered especially vulnerable by prevailing policies, structural inequalities, and stigmatisation. In this Series paper we analyse existing literature and empirical evidence from scoping reviews on integration designs for the treatment of HIV and substance use disorder, to understand barriers to and facilitators of care integration and to map ways forward. We discuss how approaches to integration address two core gaps in current models: a failure to consider human rights when incorporating the perspectives of people living with HIV and people who use drugs, and a failure to reflect critically on structural factors that determine risk, vulnerability, health-care seeking, and health equity. We argue that successful integration requires a person-centred approach, which is grounded in human rights, treats both concerns holistically, and reconnects with underlying social, economic, and political inequalities.