Why do people who use drugs use overdose prevention centres? Safety, trust and inclusion

What is it about?

Overdose prevention centres (OPCs) are facilities where people can use drugs they have obtained elsewhere in the presence of trained staff who can respond to overdoses. Many systematic reviews have established that OPCs reduce overdose deaths and improve health outcomes, but few have explained the mechanisms through which these effects occur. This realist review, conducted to RAMESES standards, systematically searched and thematically analysed 391 documents covering contexts, mechanisms and outcomes at OPCs worldwide. Using retroductive analysis, the review identifies a causal pathway centred on three interacting conditions: the immediate physical safety that an OPC provides, the trust that builds between service users and staff over repeated contact, and the social inclusion that comes from being in a non-judgemental space with others who share similar experiences. The combination of safety, trust and inclusion creates conditions through which further positive outcomes, including engagement with health and social care services, can emerge depending on local context.

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Why is it important?

Realist reviews go beyond asking whether interventions work to explain how and why they work, producing theory that can guide implementation decisions. The causal pathway identified here, anchored in safety, trust and social inclusion, provides commissioners and service designers with a model for what OPCs must deliver to achieve their potential, not simply a description of observed outcomes. The finding that safety is the foundational condition, without which trust and inclusion cannot develop, has direct implications for how OPCs should be staffed, designed and governed. The analysis of 391 documents makes this one of the most comprehensive evidence syntheses of the OPC literature to date, and the realist framework produces findings that are directly transferable to new settings, including the UK, where sanctioned OPCs remain absent despite sustained policy advocacy.