Effectiveness and cost-effectiveness of a peer-delivered, relational, harm reduction intervention to improve mental health, quality of life, and related outcomes, for people experiencing homelessness and substance use problems: The ‘SHARPS’ cluster randomised controlled trial.
Peer Navigators with lived experience of homelessness and substance use will deliver a 12-month harm reduction programme to 500 people across 20 towns and cities in England and Scotland, in a cluster randomised trial against usual care. People experiencing homelessness and problem substance use often cannot access appropriate healthcare or addiction treatment. Standard services rarely account for the relational trust and practical support needed to engage this group. The SHARPS 2 intervention fills this gap by embedding trained Peer Navigators within third-sector homelessness services, providing emotional and practical support to a caseload of up to 25 people each. If the intervention improves mental health and quality of life at 12 months, and proves cost-effective, it could offer a scalable model for integrating peer-led harm reduction into social care systems. This would directly affect how local commissioners and providers design support for one of the most excluded populations, potentially reducing substance-related harms, emergency service use, and long-term health inequalities. The process evaluation will also clarify how to transfer the model to other settings, ensuring the approach can be adopted beyond the trial sites.
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Research question Is a peer-led harm reduction relational 12-month intervention for problem substance use among people experiencing homelessness, delivered in social care settings, effective in improving mental health, quality of life, and related outcomes, and cost-effective, compared to usual care? Background People experiencing homelessness and problem substance use struggle to access appropriate physical and mental healthcare and problem drug/alcohol treatment. There is growing recognition of the value of people with lived experience of related conditions, in this case substance use and homelessness, called Peer Navigators (PNs), supporting access to wider health and social care, treatment and social supports. Aims/Objectives To evaluate the effectiveness and cost-effectiveness of the SHARPS 2 intervention for people experiencing homelessness and problem substance use. Primary objectives: Conduct a 12-month intervention via a cluster RCT to determine whether it improves mental health and quality of life compared to usual care; compare secondary outcomes of substance use/harms, risk-taking behaviour, social functioning/support, physical health, service utilisation, and therapeutic alliance; and undertake a cost-effectiveness evaluation. Secondary objectives: Conduct a process evaluation to examine implementation, intervention fit, and transferability to wider settings; assess intervention fidelity. Methods Design: 2-arm pragmatic cluster RCT across 20 clusters (cities/towns) in England and Scotland. Health technology: Co-produced intervention delivered by PNs based in third sector homelessness services in 10 towns/cities, who provide emotional and practical support to a caseload of up to 25 people for 12 months. Inclusion criteria: >18 years old; experiencing/at risk of homelessness; (self-report) problem substance use. Exclusion criteria: participation in other substance use studies; inability to give clear informed consent due to ongoing serious mental illness or cognitive impairment; posing a safety risk to staff members/PN; non-English speaking. Primary outcomes: mental health (PHQ-ADS) and quality of life (ICECAP-A) at 12m after baseline measurement. Secondary outcomes: PHQ-ADS and ICECAP-A at 6 and 15m; harmful substance use (MAP, LDQ), risk taking behaviours (MAP), social functioning (MAP), physical health (MAP, EQ-5D-5L), social outcomes (SSQ, ISEL, IPDA), therapeutic alliance/accessibility and service utilisation (MAP, CEST), and relational empathy (CARE measure), all up to 15 months; cost effectiveness (QALYs and costs). Process evaluation: Mixed methods process evaluation; focus on participant, PN and wider staff experiences, to inform future implementation, transferability; measure intervention fidelity. Sample size 500 participants from 20 clusters for 90% power to detect 0.076 difference on ICECAP-A and 5 on PHQ-ADS at 12 months (assuming an ICC of 0.01 and 40% attrition). Timelines for delivery Study set up 1-10m (cluster randomisation, PN recruitment/training, baseline data collection); intervention delivery and process evaluation 7-29m; participant follow-up 21-28m; analysis & dissemination 29-36m. Impact and dissemination Findings will be presented in high-impact journals and conferences; plain English summaries/briefings via blogs and videos through social and other media and via in person stakeholder events in services to inform commissioners/providers, policy makers and lay/citizen/advocacy groups.
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