Authors' objectives: The barriers and facilitators to engagement with Opiate Substitute Treatment and Needle and Syringe Provision need to be better understood to develop interventions to attract people into services. We conducted a multi-method realist evaluation to generate an in-depth theory of the factors that influence the optimal provision of services in terms of access, engagement, retention and successful exit. Illicit drug use is an escalating problem in the UK, which now has one of the highest estimated populations of people who use drugs in Western Europe. Injecting drug use is associated with numerous health-related harms, including a high incidence of blood-borne virus infection, soft-tissue and skin infection, premature mortality from overdose, suicide and other causes of death. Two central elements of global, European and UK’s harm reduction approach in relation to illicit drug use are opiate substitution therapy (OST) and needle and syringe programmes (NSPs). Engagement and retention in OST is a recognised problem globally. To prevent and reduce further harms, it is imperative that different models of service provision are better understood to attract and retain more service users in harm reduction services. The overall aim of the study was to generate a theory of optimal service provision with in-depth knowledge of the contextual factors and the mechanisms that influence access, engagement, retention and exit of OST/NSP services. We conducted a multi-method realist evaluation (RE) over two phases to meet four study objectives. Phase 1 Objective 1: To conduct a meta-synthesis (MS) of qualitative studies using systematic review methods to identify the barriers and facilitators that impact on the use of OST and NSP services. Objective 2: To conduct a UK-wide online survey of service commissioners to map current models of OST prescribing and practices to better understand current service provision/delivery.

Authors' results and conclusions: Findings indicated that optimal provision could be understood with reference to five main contexts [(1) agency and empowerment, (2) self-esteem and respect, (3) knowledge and communication, (4) goals, needs and preferences and (5) resources and demands]. The analysis suggested that optimal provision could be facilitated via specific mechanisms of action, operating at the ‘Systems level’ (policy, legislation and funding) and ‘Service level’ (delivery of services, service pathways, staff roles and responsibilities and organisational culture). Our analysis also identified the potential importance of independent ‘mediating mechanisms’ (e.g. confidence, trust and self-efficacy) which can operate to increase the likelihood of successful service outcomes. A costing analysis estimated the costs associated with a smaller caseload for shared care workers and the implementation of a salary increment scheme at one of the study sites. We have provided a rich understanding of the contexts, mechanisms and actions by which optimal delivery of Opiate Substitute Treatment and Needle and Syringe Provision services may increase the likelihood of successful service provision. A multiagency approach applying various mechanisms within the various contexts of optimal provision may need to be implemented to optimise the provision. Meta-synthesis From 63 included studies (53 OST-related and 10 NSP-related), it was noted that none included the views of commissioners of services; thus their views are absent. Twenty of the included studies (13 OST and 7 NSP) included a total of 449 (15%) staff participants, and 53 studies (45 OST and 8 NSP) included a total of 2518 (85%) service user participants. The views of staff, and to a much greater extent, service users, are therefore well represented in the MS. Studies were conducted across a wide range of countries (mainly North America), with nine being conducted in the UK (six OST/three NSP). The majority (n = 31) were published within the previous 5 years. The barriers and facilitators identified in the MS significantly contribute to our understanding of four important ‘contexts’ within which services are delivered. Within these contexts, the barriers and facilitators that were identified contributed towards hypothesised mechanisms that could lead to optimal provision regarding successful access, engagement, retention and exit. This contributed significantly to the identification of an initial programme theory (IPT) of how services can ensure optimal service provision. We have provided a rich understanding of the contexts, mechanisms and actions by which the optimal delivery of OST and NSP services may be understood in order to increase the likelihood of successful access to, engagement with, retention in and exit from services. Services may wish to consider how well they are currently operating regarding the contexts and mechanisms we have identified and to determine where they may be deficient and then use the descriptions we have provided as a road map to make improvements in those areas.

Authors' methods: Multi-method involving an online survey of United Kingdom drug and alcohol service commissioning leads and a meta-synthesis of qualitative literature (phase 1) to facilitate the development of an initial theory of optimal provision; and, in phase 2, a realist evaluation to test and refine the initial theory, involving in-depth interviews across three United Kingdom sites, with service commissioners, managers, staff and service users. We used routine treatment and staffing data to estimate the additional staff costs of implementing optimal service provision within one context of our refined theory. The survey sample size limited generalisability. There was a limited number of United Kingdom studies within the meta-synthesis. The findings of the realist evaluation highlight that provision was not optimised in the observed sites, limiting examples of best practice. However, the conceptual theory of optimal provision can direct future research to facilitate the development and implementation of optimal policy and practice. Patient and public involvement took place throughout the study. Meta-synthesis methods We conducted a systematic review and MS of qualitative studies. A prior protocol was published: PROSPERO 2020 CRD42020209646; available from: www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020209646. A sensitive search strategy was developed and then run in multiple online research databases in January 2021: MEDLINE; Cumulative Index to Nursing and Allied Health Literature; British Nursing Index and Archive; Applied Social Science Index and Abstracts; Social Sciences Citation Index and PsycInfo® (American Psychological Association, Washington, DC, USA). In addition, the following grey literature sources were searched: OpenGrey and PsycEXTRA. Any primary or secondary qualitative studies conducted anywhere in the world that sought to understand the optimal provision of NSP and OST services from the perspectives of key stakeholders were included. Studies should have been seeking to understand issues regarding: Access, Engagement, Retention and Exits of OST and/or NSP. All included publications were subject to a global assessment of study quality. Drawing on methods proposed by Noblit and Hare, data synthesis was rigorous and multistaged.

Project Status: Completed

URL for project: https://www.journalslibrary.nihr.ac.uk/programmes/hta/NIHR129798

Year Published: 2025

URL for published report: https://www.journalslibrary.nihr.ac.uk/hta/HGDS4449

URL for additional information: English

English language abstract: An English language summary is available

Publication Type: Full HTA

Country: England, United Kingdom

DOI: 10.3310/HGDS4449

Organisation Name: NIHR Health Technology Assessment programme

Contact Address: NIHR Journals Library, National Institute for Health and Care Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK

Contact Name: journals.library@nihr.ac.uk

Contact Email: journals.library@nihr.ac.uk