Optimal provision of opioid agonist therapy (OAT) and needle and syringe programmes (NSP): a realist evaluation

Peter McCulloch; Hannah Family; April Shaw; Gabriele Vojt; Gail Gilchrist; Catriona Matheson; Margaret Maxwell; Joanne Neale; Gareth Myring; Hugh McLeod; Matthew Hickman; Peter Vickerman; Alison Munro; Steve MacGillivray

doi:10.1016/j.drugpo.2026.105174

Optimal provision of opioid agonist therapy (OAT) and needle and syringe programmes (NSP): a realist evaluation

Peter McCulloch^*
, Hannah Family
, April Shaw
, Gabriele Vojt
, Gail Gilchrist
, Catriona Matheson
, Margaret Maxwell
, Joanne Neale
, Gareth Myring
, Hugh McLeod
, Matthew Hickman
, Peter Vickerman
, Alison Munro
, Steve MacGillivray

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

Abstract

Background
Understanding the factors that hinder or support engagement with Opioid Agonist Therapy (OAT) and Needle and Syringe Provision (NSP) is essential for increasing retention and reducing drug-related harm. This study comprised a multimethod realist evaluation to develop a theory of the factors influencing service provision, focusing on access, engagement, retention, and successful exit (clients outcome met) from services.

Design
Phase 1 involved an online survey of UK drug and alcohol service commissioners, focus groups with interest holders, and a qualitative systematic review to build an initial programme theory of optimal service provision. Phase 2 tested and refined this theory through 86 in-depth interviews across three UK sites with commissioners, managers, staff, and people who use services (both regular attendees and those with limited contact).

Results
The Realist Evaluation identified five interrelated contexts (Agency and Empowerment; Self-esteem and Respect; Knowledge and Communication; Goals, Needs and Preferences; and Resources and Demands), within which mechanisms can shape optimal service provision. Person-centred approaches, low-threshold access, and timely provider contact foster agency. Confidentiality, non-stigmatising care, and strengths-based support build self-esteem, while skilled staff, training, and peer networks enhance knowledge and communication. Flexible appointments, integrated services, and shared stakeholder responsibility align care with individual goals and needs. Adequate staffing, training, supervision, and sustainable funding enable responsive, resilient services.

Conclusions
These findings show how interacting relational and structural mechanisms generate optimal outcomes, guiding policy and service design. Implementing a multi-agency approach, integrating different mechanisms across the identified contexts, may be necessary to achieve optimal service delivery.

Original language	English
Article number	105174
Number of pages	13
Journal	International Journal of Drug Policy
Volume	150
Early online date	20 Feb 2026
DOIs	https://doi.org/10.1016/j.drugpo.2026.105174
Publication status	E-pub ahead of print - 20 Feb 2026
Externally published	Yes

Keywords

opioid agonist therapy (OAT)
needle and syringe provision (NSP)
harm reduction
realist evaluation
person-centred care
whole-systems approach
agency and empowerment
self-esteeem and respect
knowledge and communication
goals, needs and preferences
resources and demands

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10.1016/j.drugpo.2026.105174Licence: CC BY-NC

2026 01 22 McCulloch et al OAT finalFinal published version, 4.19 MBLicence: CC BY-NC

Cite this

McCulloch, P., Family, H., Shaw, A., Vojt, G., Gilchrist, G., Matheson, C., Maxwell, M., Neale, J., Myring, G., McLeod, H., Hickman, M., Vickerman, P., Munro, A., & MacGillivray, S. (2026). Optimal provision of opioid agonist therapy (OAT) and needle and syringe programmes (NSP): a realist evaluation. International Journal of Drug Policy, 150, Article 105174. Advance online publication. https://doi.org/10.1016/j.drugpo.2026.105174

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abstract = "Background Understanding the factors that hinder or support engagement with Opioid Agonist Therapy (OAT) and Needle and Syringe Provision (NSP) is essential for increasing retention and reducing drug-related harm. This study comprised a multimethod realist evaluation to develop a theory of the factors influencing service provision, focusing on access, engagement, retention, and successful exit (clients outcome met) from services. Design Phase 1 involved an online survey of UK drug and alcohol service commissioners, focus groups with interest holders, and a qualitative systematic review to build an initial programme theory of optimal service provision. Phase 2 tested and refined this theory through 86 in-depth interviews across three UK sites with commissioners, managers, staff, and people who use services (both regular attendees and those with limited contact). Results The Realist Evaluation identified five interrelated contexts (Agency and Empowerment; Self-esteem and Respect; Knowledge and Communication; Goals, Needs and Preferences; and Resources and Demands), within which mechanisms can shape optimal service provision. Person-centred approaches, low-threshold access, and timely provider contact foster agency. Confidentiality, non-stigmatising care, and strengths-based support build self-esteem, while skilled staff, training, and peer networks enhance knowledge and communication. Flexible appointments, integrated services, and shared stakeholder responsibility align care with individual goals and needs. Adequate staffing, training, supervision, and sustainable funding enable responsive, resilient services. Conclusions These findings show how interacting relational and structural mechanisms generate optimal outcomes, guiding policy and service design. Implementing a multi-agency approach, integrating different mechanisms across the identified contexts, may be necessary to achieve optimal service delivery.",

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author = "Peter McCulloch and Hannah Family and April Shaw and Gabriele Vojt and Gail Gilchrist and Catriona Matheson and Margaret Maxwell and Joanne Neale and Gareth Myring and Hugh McLeod and Matthew Hickman and Peter Vickerman and Alison Munro and Steve MacGillivray",

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doi = "10.1016/j.drugpo.2026.105174",

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McCulloch, P, Family, H, Shaw, A, Vojt, G, Gilchrist, G, Matheson, C, Maxwell, M, Neale, J, Myring, G, McLeod, H, Hickman, M, Vickerman, P, Munro, A & MacGillivray, S 2026, 'Optimal provision of opioid agonist therapy (OAT) and needle and syringe programmes (NSP): a realist evaluation', International Journal of Drug Policy, vol. 150, 105174. https://doi.org/10.1016/j.drugpo.2026.105174

TY - JOUR

T1 - Optimal provision of opioid agonist therapy (OAT) and needle and syringe programmes (NSP)

T2 - a realist evaluation

AU - McCulloch, Peter

AU - Family, Hannah

AU - Shaw, April

AU - Vojt, Gabriele

AU - Gilchrist, Gail

AU - Matheson, Catriona

AU - Maxwell, Margaret

AU - Neale, Joanne

AU - Myring, Gareth

AU - McLeod, Hugh

AU - Hickman, Matthew

AU - Vickerman, Peter

AU - Munro, Alison

AU - MacGillivray, Steve

PY - 2026/2/20

Y1 - 2026/2/20

N2 - Background Understanding the factors that hinder or support engagement with Opioid Agonist Therapy (OAT) and Needle and Syringe Provision (NSP) is essential for increasing retention and reducing drug-related harm. This study comprised a multimethod realist evaluation to develop a theory of the factors influencing service provision, focusing on access, engagement, retention, and successful exit (clients outcome met) from services. Design Phase 1 involved an online survey of UK drug and alcohol service commissioners, focus groups with interest holders, and a qualitative systematic review to build an initial programme theory of optimal service provision. Phase 2 tested and refined this theory through 86 in-depth interviews across three UK sites with commissioners, managers, staff, and people who use services (both regular attendees and those with limited contact). Results The Realist Evaluation identified five interrelated contexts (Agency and Empowerment; Self-esteem and Respect; Knowledge and Communication; Goals, Needs and Preferences; and Resources and Demands), within which mechanisms can shape optimal service provision. Person-centred approaches, low-threshold access, and timely provider contact foster agency. Confidentiality, non-stigmatising care, and strengths-based support build self-esteem, while skilled staff, training, and peer networks enhance knowledge and communication. Flexible appointments, integrated services, and shared stakeholder responsibility align care with individual goals and needs. Adequate staffing, training, supervision, and sustainable funding enable responsive, resilient services. Conclusions These findings show how interacting relational and structural mechanisms generate optimal outcomes, guiding policy and service design. Implementing a multi-agency approach, integrating different mechanisms across the identified contexts, may be necessary to achieve optimal service delivery.

AB - Background Understanding the factors that hinder or support engagement with Opioid Agonist Therapy (OAT) and Needle and Syringe Provision (NSP) is essential for increasing retention and reducing drug-related harm. This study comprised a multimethod realist evaluation to develop a theory of the factors influencing service provision, focusing on access, engagement, retention, and successful exit (clients outcome met) from services. Design Phase 1 involved an online survey of UK drug and alcohol service commissioners, focus groups with interest holders, and a qualitative systematic review to build an initial programme theory of optimal service provision. Phase 2 tested and refined this theory through 86 in-depth interviews across three UK sites with commissioners, managers, staff, and people who use services (both regular attendees and those with limited contact). Results The Realist Evaluation identified five interrelated contexts (Agency and Empowerment; Self-esteem and Respect; Knowledge and Communication; Goals, Needs and Preferences; and Resources and Demands), within which mechanisms can shape optimal service provision. Person-centred approaches, low-threshold access, and timely provider contact foster agency. Confidentiality, non-stigmatising care, and strengths-based support build self-esteem, while skilled staff, training, and peer networks enhance knowledge and communication. Flexible appointments, integrated services, and shared stakeholder responsibility align care with individual goals and needs. Adequate staffing, training, supervision, and sustainable funding enable responsive, resilient services. Conclusions These findings show how interacting relational and structural mechanisms generate optimal outcomes, guiding policy and service design. Implementing a multi-agency approach, integrating different mechanisms across the identified contexts, may be necessary to achieve optimal service delivery.

KW - opioid agonist therapy (OAT)

KW - needle and syringe provision (NSP)

KW - harm reduction

KW - realist evaluation

KW - person-centred care

KW - whole-systems approach

KW - agency and empowerment

KW - self-esteeem and respect

KW - knowledge and communication

KW - goals, needs and preferences

KW - resources and demands

U2 - 10.1016/j.drugpo.2026.105174

DO - 10.1016/j.drugpo.2026.105174

M3 - Article

SN - 0955-3959

VL - 150

JO - International Journal of Drug Policy

JF - International Journal of Drug Policy

M1 - 105174

ER -

Optimal provision of opioid agonist therapy (OAT) and needle and syringe programmes (NSP): a realist evaluation

Abstract

Keywords

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