Background: The transition from adolescence to young adulthood (age 10‐25 years) constitutes a sensitive developmental period marked by rapid biological, psychological, and social change, during which preventive health interventions can shape long-term outcomes. Mobile health tools offer accessible opportunities for tailored support for this population, but often adapt poorly to dynamic contexts, resulting in inconsistent engagement and effects. Just-in-time adaptive interventions (JITAIs), which tailor support in real time using ongoing data, are increasingly explored as precision health strategies. However, how these mechanisms are designed, implemented, and evaluated for adolescents and young adults (AYAs) has not been systematically reviewed. Objective: This review aimed to synthesize the evidence on JITAIs developed for AYAs, examine how their adaptive mechanisms have been designed to support specific health goals and changing AYA contexts, and assess methodological reporting quality to inform future precision health intervention development. Methods: We conducted a systematic review in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and SWiM (Synthesis Without Meta-Analysis) reporting guidelines. Twelve databases were searched for peer-reviewed studies published from 2013 to 2025. Eligible studies focused on participants aged 10 to 25 years and reported real-time adaptive mobile health interventions consistent with JITAI design principles. Two reviewers independently conducted screening, data extraction, and methodological quality appraisal using the Joanna Briggs Institute checklists. AYA coauthors contributed to all phases. Due to substantial heterogeneity in study populations, intervention content, adaptive mechanisms, comparators, and outcome measurements, findings were synthesized narratively, and no meta-analysis was conducted. Results: A total of 61 unique interventions were included. JITAIs for AYAs addressed substance use (n=24, 39.3%), mental health (n=23, 37.7%), and physical health or chronic conditions (n=14, 23%). JITAI tailoring mechanisms relied predominantly on self-reported behavioral data. Decision rules were typically symptom threshold–based, and decision points were commonly daily or event-triggered. Methodological concerns with reporting on intervention administration, participant selection, and outcome measurement reliability were pervasive across all studies, limiting the interpretability of observed effects and cross-study comparisons. Ethical considerations, including researcher positioning and reflexivity, alongside the depth of reporting around participatory AYA engagement in design and implementation, were also inconsistent. Conclusions: This review contributes a novel perspective to AYA digital health by moving beyond intervention outcomes to examine how core adaptive mechanisms are operationalized for AYAs across multiple health domains, while also integrating AYA perspectives into the interpretation of findings and recommendations. Unlike prior reviews focused primarily on adults or specific conditions, it identifies broader contextual, methodological, and ethical considerations relevant to AYA precision health. These findings highlight the need for more transparent, contextually responsive, and youth-centered adaptive interventions, alongside more rigorous designs for evaluating adaptive intervention components in daily life contexts.

Paediatric palliative care (PPC) aims to improve the quality of life of children with life-limiting and life-threatening conditions. PPC addresses the needs of both the child and family and preferably starts immediately after a palliative diagnosis. It includes effective symptom management, psychosocial, spiritual and emotional support. Receiving PPC is often challenging due to the varied and complex nature of conditions and the difficulties in reaching all children who require palliative care. Telehealth offers a promising solution by enabling virtual access to interdisciplinary teams, facilitating real-time consultations, extending care into the home, educating professionals across regions and fostering consistent, collaborative, patient- and family-centred PPC. As this requires a seamless integration into the daily routines of all relevant stakeholders, telehealth may raise complexity in terms of privacy, data protection and regulatory compliance. Nevertheless, studies indicate that parents and children are open to using telehealth applications.Since the COVID-19 pandemic, telehealth development in paediatrics showed a rapid and substantial scale-up. Evaluating the quality of these new technical solutions remains important. One of the main outcome measures used in telehealth evaluation studies is quality of care. Currently, the literature has no consensus on which quality of care metrics can be used to assess the development, implementation and evaluation of telehealth solutions in home-care PPC. In addition, a timely update on the fast-growing field of telehealth solutions in PPC is required. Therefore, this study aims to update and examine quality of care metrics in telehealth solutions for PPC, contributing to the conceptual foundation for the development, implementation and evaluation of home-based PPC telehealth services. Findings from our review will contribute to a deeper understanding of how children and families can receive timely and accessible palliative care regardless of their location, ultimately informing future telehealth models and research projects. METHODS AND ANALYSIS: Our systematic review will evaluate studies that describe telehealth solutions in PPC home-care settings, using the Cochrane handbook, and the reporting will follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We will include peer-reviewed articles without language or geographical restrictions. The search will be conducted by an information specialist and data synthesis will be documented via a data extraction table in MS Excel. Along with a Mixed-Method-Appraisal-Tool (MMAT) quality appraisal, data extraction will be managed by Covidence. Two reviewers will screen and extract data independently, with a third reviewer resolving discrepancies. We will present a narrative synthesis, using clear language, defining key terms and following open-access standards to ensure accessibility for non-expert audiences. ETHICS AND DISSEMINATION: No primary or clinical data will be collected. Therefore, ethical approval is not relevant. Review findings will be shared via peer-reviewed journal publications, conferences, stakeholder meetings and online presentations. PROSPERO REGISTRATION NUMBER: CRD420251035350.

Introduction Health behaviours such as exercise and diet strongly influence well-being and disease risk, providing the opportunity for interventions tailored to diverse individual contexts. Precise behaviour interventions are critical during adolescence and young adulthood (ages 10-25), a formative period shaping lifelong well-being. We will conduct a systematic review of just-in-time adaptive interventions (JITAIs) for health behaviour and well-being in adolescents and young adults (AYAs). A JITAI is an emerging digital health design that provides precise health support by monitoring and adjusting to individual, specific and evolving contexts in real time. Despite demonstrated potential, no published reviews have explored how JITAIs can dynamically adapt to intersectional health factors of diverse AYAs. We will identify the JITAIs' distal and proximal outcomes and their tailoring mechanisms, and report their effectiveness. We will also explore studies' considerations of health equity. This will form a comprehensive assessment of JITAIs and their role in promoting health behaviours of AYAs. We will integrate evidence to guide the development and implementation of precise, effective and equitable digital health interventions for AYAs. Methods and analysis In adherence to Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines, we will conduct a systematic search across multiple databases, including CENTRAL, MEDLINE and WHO Global Index Medicus. We will include peer-reviewed studies on JITAIs targeting health of AYAs in multiple languages. Two independent reviewers will conduct screening and data extraction of study and participant characteristics, JITAI designs, health outcome measures and equity considerations. We will provide a narrative synthesis of findings and, if data allows, conduct a meta-analysis. Ethics and dissemination As we will not collect primary data, we do not require ethical approval. We will disseminate the review findings through peer-reviewed journal publication, conferences and stakeholder meetings to inform participatory research. PROSPERO registration number CRD42023473117.