Worldwide, the division between Child and Adolescent Mental Health Services (CAMHS) and Adult Mental Health Services (AMHS) has frequently resulted in fragmented care with an unprepared, non-gradual transition. To improve continuity of care and other service transition experiences, service user input is essential. However, such previous qualitative studies are from a decade ago or focused on one mental disorder or country. The aim of the present study was to learn from service users’ transition experiences and suggested improvements.

Semi-structured interviews were held with young people aged 18–24 and/or parents/caregivers in the United Kingdom, Ireland, the Netherlands and Croatia. Inclusion was based on the experience of specialist mental health care before and after turning 18. Thematic analysis of transcribed and translated interview transcripts was performed using ATLAS.ti 9.

Main themes of service user experiences included abrupt changes in responsibilities, various barriers and a lack of preparation, communication and ongoing care. Young people expressed a great need for continuity of care. Their suggestions to improve transitional care included early and adequate preparation, joint working, improved communication from and between services, overlapping services, staying at CAMHS for longer and designated youth mental health teams.

Young people who experienced care before and after turning 18 suggested either altering the age limits of services or ensuring early preparation and communication regarding the transition and finding AHMS. This communication should include general changes when turning 18. Further considerations include increasing collaboration and overlap between CAMHS and AMHS.

The boundary between services for children and adolescents and adults has been identified as problematic for young people with mental health problems.

To examine the use and cost of healthcare for young people engaged in mental healthcare before and after the child/adolescent and adult service boundary.

Data from 772 young people in seven European countries participating in the MILESTONE trial were analysed. We analysed and costed healthcare resources used in the 6-month period before and after the service boundary.

The proportion of young people engaging with healthcare services fell substantially after crossing the service boundary (associated costs €7761 pre-boundary v. €3376 post-boundary). Pre-boundary, the main cost driver was in-patient care (approximately 50%), whereas post-boundary costs were more evenly spread between services; cost reductions were correlated with pre-boundary in-patient care. Severity was associated with substantially higher costs pre- and post-boundary, and those who were engaged specifically with mental health services after the service boundary accrued the greatest healthcare costs post-service boundary.

Costs of healthcare are large in this population, but fall considerably after transition, particularly for those who were most severely ill. In part, this is likely to reflect improvement in the mental health of young people. However, qualitative evidence from the MILESTONE study suggests that lack of capacity in adult services and young people's disengagement with formal mental health services post-transition are contributing factors. Long-term data are needed to assess the adverse long-term effects on costs and health of this unmet need and disengagement.