The working alliance (WA), a collaborative relationship between client and therapist, is crucial in adult psychotherapy for anxiety and depression. However, its role in low-intensity therapies for young people remains under-researched. This study addresses this gap by exploring the impact of WA on anxiety and depression outcomes in youth aged 14–24 years using a scoping review and stakeholder consultations. The study aims to understand how WA influences treatment outcomes and identify factors affecting this relationship. The importance stems from the high prevalence of mental health problems in youth, highlighting the urgent need to improve the effectiveness of interventions. Understanding the mechanisms through which treatments work, such as the role of WA, is crucial for optimizing treatment and prevention strategies. The Active Ingredients commission, funded by the Welcome Trust, prompted this research, aiming to identify essential elements for the effective management of anxiety and depression in young people. This initiative goes beyond previous reviews by incorporating the perspectives of young people with lived experience, providing valuable insights into their experience of the therapeutic process and what contributes to forming a successful working alliance.

Systematic reviews predominantly focused on adults have shown a strong positive correlation between a functional WA and positive treatment outcomes across various psychotherapies. A functional WA is characterized by three core elements: the bond between client and therapist, agreement on therapy goals, and agreement on the tasks needed to achieve those goals. Studies consistently demonstrate that a strong WA is associated with improved treatment adherence, higher engagement levels, and better symptom reduction. Conversely, a weak or ruptured WA often leads to reduced treatment effectiveness. However, research specifically focusing on young people is limited, with existing studies offering inconclusive evidence on the mechanisms behind this relationship. While some studies have examined the role of WA in cognitive behavioral therapy (CBT) and family-involved therapies for youth, further research is needed to fully understand its significance in individual and low-intensity therapies. This lack of clarity on the mechanisms of WA and its specific impact on youth mental health highlights the importance of this study.

This mixed-methods study employed a scoping review complemented by stakeholder consultations. **Scoping Review:** A comprehensive search of databases (PubMed, CINAHL, Scopus, PsychINFO, Africa-Wide Information) yielded 274 records. After removing duplicates and applying eligibility criteria (quantitative studies, participants aged 14–24 years, English language), 27 studies were included in the qualitative synthesis. Data extraction focused on author, year, age group, outcomes, and findings. The PRISMA-SCR checklist guided the review process. **Eligibility Criteria:** The inclusion criteria for studies involved in the scoping review were quantitative study designs, focus on young people aged 14-24 with anxiety and/or depression, and publication in the English language. Studies that did not meet these criteria were excluded. **Search Strategy:** Databases were searched using relevant keywords, combined with Boolean operators, to identify studies focusing on working alliances, anxiety, depression, and young people. **Stakeholder Consultations:** Semi-structured interviews were conducted with 32 stakeholders, including young people with lived experience (n=20), lay health counselors, psychologists, occupational therapists, and psychiatrists. The interviews explored WA elements considered important by both youth and therapists, as well as factors influencing the WA-outcome relationship. Thematic analysis was used to analyze qualitative data. **Data Synthesis and Validation Workshops:** Two workshops were conducted to synthesize findings from the scoping review and stakeholder consultations. Young people with lived experience played a crucial role in reviewing and validating the findings.

The scoping review revealed that most included studies (26/27) were from high-income countries, primarily the US. CBT was the most common intervention. The Working Alliance Inventory (WAI) was the most frequently used measurement tool. Most studies showed a positive association between WA and clinical outcomes (24/27), indicating that a stronger working alliance generally leads to better treatment outcomes for young people with anxiety and depression. **Scoping Review Findings:** * The majority of studies (26/27) were conducted in high-income countries, mainly the US. * CBT was the most frequently used treatment modality. * The Working Alliance Inventory was the most common outcome measure. * Most studies (24/27) demonstrated a positive association between WA and clinical outcomes. **Stakeholder Consultations Findings:** * **Young People:** Highlighted the importance of a conducive environment, regular sessions, confidentiality, and collaborative goal setting in building a strong WA. They also emphasized the importance of a trusting and empathetic therapist. * **Clinicians:** Emphasized the importance of setting boundaries, maintaining confidentiality, using excellent communication skills, being non-judgmental and empathetic in facilitating a functional WA. They also considered goal setting and client motivation as crucial factors. **Synthesis of Findings:** A functional WA, built upon a strong bond, shared goals, and agreed-upon tasks, was seen as a key active ingredient in improving outcomes for youth with anxiety and depression. This leads to increased treatment adherence, self-esteem, satisfaction, improved relationships, and coping skills, ultimately leading to better mental health.

This study confirms the importance of WA as an active ingredient in youth psychotherapy for anxiety and depression, aligning with research on adults. Improved WA is associated with improvements in various psychosocial factors, potentially creating a positive feedback loop that enhances mental health and further strengthens the WA. While the precise mechanism remains unclear, improvements in bond and task completion seem particularly important. Pre-treatment client characteristics such as motivation, hope, and treatment expectancy influence WA formation. Conversely, relationship problems or certain personality disorders might hinder the positive impact of WA. Therapist characteristics, including empathy and experience, also significantly influence the development and maintenance of a positive WA. Treatment modalities, delivery modes (in-person vs. online), and settings (inpatient vs. outpatient) also influence the WA-outcome association, although evidence is still emerging. Specifically, there is not conclusive evidence whether experience levels play a substantial role, and further research needs to be done regarding the optimal timing of WA assessment and long-term effects.

This scoping review and stakeholder consultations strongly suggest that a functional working alliance is a crucial active ingredient in improving outcomes for young people experiencing anxiety and depression. Routine evaluation of WA is recommended. Future research should focus on longitudinal studies, utilizing robust methodologies and advanced statistical techniques to clarify the mechanisms by which WA works and address the limitations of this study. This includes investigating the influence of cultural contexts and further exploring the role of WA in different therapeutic settings and modalities.

The study's generalizability might be limited due to the overrepresentation of studies from high-income countries and the lack of formal bias assessment. Few studies exclusively focused on the 14-24 age group. Heterogeneity in WA measurement tools also poses a challenge. While stakeholder consultations provided valuable insights, the lack of quantitative data from low-income countries limits the generalizability of findings.