The care responders study: a realist synthesis of police–clinician joint and co-response models for youth mental health crises

Mental health crises among children and young people are increasingly recognised as a public health priority. In response, co- and joint-response models, where professionals from across the emergency services work together with mental health practitioners, have emerged internationally as alternatives to traditional police-led or solely health-led interventions, recognising the complex and multifaceted nature of mental health crises, the need for fast responses, and often complex situations requiring multidisciplinary expertise. These models aim to reduce harm, improve access to non-restrictive care, and foster trauma-responsive, developmentally appropriate responses. However, their effectiveness varies across contexts, and concerns persist regarding equity, sustainability, and the quality of research to underpin the emerging evidence base of these models. This realist review explored how, why, for whom, and in what contexts co-response models can support young people experiencing mental health crises. Following RAMESES guidelines, systematic searches were conducted across six databases and grey literature sources. Inclusion criteria focused on emergency responses for individuals aged 0–25, incorporating diverse study designs and stakeholder perspectives. Data were extracted and synthesised using context–mechanism–outcome configurations (CMOCs), refined based on 32 semi-structured interviews with professionals and people with lived experience. Of 6, 174 records identified, 45 articles met inclusion criteria. Fourteen CMOCs were developed and grouped into three thematic domains: (1) youth and caregiver experience and outcomes, (2) workforce experiences and collaboration, and (3) organisational impacts and implementation factors. Effective co-response models were characterised by calm, participatory communication, cross-agency collaboration, and system-level enablers such as stable funding and interoperable information systems. These contributed to reduced trauma, fewer emergency department presentations, and improved decision-making for patient care. Conversely, police-only responses without clinical support heightened distress and increased restrictive interventions. Overarching factors, including stigma, ethical concerns, and legal frameworks, shaped implementation and outcomes. Co-response models can offer safer, trauma-responsive and equitable crisis care for young people when embedded within well-resourced, clearly governed systems. This paper highlights the need for sustained investment and coordinated strategies to strengthen co- and joint-response crisis response systems for young people. Key priorities include integrating mental health expertise, fostering police–clinician collaboration, adopting trauma-responsive and culturally responsive practices, and ensuring robust governance and data systems to support long-term impact.