Abstract
BACKGROUND: Overdose prevention centres (OPCs) are spaces where people can consume previously obtained illicit drugs under the supervision of staff who can intervene to prevent and manage overdose. They have been provided in Europe and elsewhere for nearly 40 years, initially in response to the epidemic of HIV/AIDS. We can learn from their operation history to inform future developments in harm reduction services. METHODS: We carried out a realist review of 391 documents, reported according to the RAMESES I guidelines, and carried out realist synthesis of these documents. RESULTS: We present a full realist programme theory of OPCs, with a diagrammatic logic model, of how the contexts and mechanisms of OPCs combine to produce various outcomes for service users and their communities in different settings. Three specific causal pathways were evidenced through which OPCs produce their outcomes for particular groups in specific contexts of housing status, gender identity and ethnicity, and local drug markets, with frequency of use, legal and political contexts, and stigma as overlapping contextual factors. Key OPC interventions include the provision of a safe and hygienic consumption space, safe consumption education, timely overdose response, and protection from drug scene and gender-based violence. These can trigger the underlying mechanisms of safety, trust, social inclusion, engagement, autonomy, and empowerment when supported with health care and other services, including detoxification and opioid agonist treatment. The combinations of these contexts and mechanisms create important outcomes for individual service users, for the communities they live in, and for wider society. We also describe causal pathways that can lead to unintended, adverse outcomes. CONCLUSION: This review provides useful information for policy makers, practitioners, and researchers on how to implement and evaluate OPCs in future to maximise their benefits; an important task in the context of the ongoing public health crises of drug poisoning deaths in North America and the UK, and the possibility of increasing deaths from synthetic opioids in Europe and elsewhere.