"Trying to get down here when the dealer's closer": Place and participation in clinical trials for substance use disorders.

Place-based substance use research has emphasized how geography, institutions, and relationships shape drug use risks and meanings. Building on this work, we examine how people who use drugs navigate the spatial and institutional landscapes of clinical research by nesting a qualitative study within a multisite pragmatic trial of opioid use disorder treatment in Canada. Drawing on 111 interviews with 72 participants across four Canadian provinces, we investigate how trial engagement unfolded within the meaningful geographies of participants' everyday lives. Participants described how spatial features (e.g., proximity to policed "drugscapes"), institutional norms (e.g., surveillance, pharmacy policies), and interactions with institutional actors (e.g., stigma, support) shaped their research experiences. Sustaining participation often required the work of mobilizing social networks, applying local knowledge, and adapting daily routines. These findings highlight the equity implications of conducting research with structurally marginalized populations and demonstrate how social, spatial, and institutional conditions shape study participation, complicating assumptions of standardization in multisite trials.