Interventions to Reduce Loneliness in Young People (10–25). Exploring the impact of theory application and digital context: Protocol for a Systematic Review and Meta-Analysis

This systematic review and meta-analysis examines the effectiveness of psychosocial interventions aiming to reduce loneliness in young people aged 10–25 years, with a particular focus on how and why these interventions work in contemporary digital contexts. Loneliness in adolescence and emerging adulthood has increased markedly over the past two decades and is associated with significant mental, physical, and socioeconomic harms. While many interventions report modest average benefits, there remains limited clarity regarding the mechanisms of change underpinning successful interventions, especially for younger populations growing up in highly digitalised social environments. The project consists of a systematic review and meta-analysis of controlled intervention studies published between 2000 and 2025. It synthesises quantitative evidence from randomised and quasi-experimental studies that evaluate psychosocial interventions targeting loneliness as a primary or secondary outcome. Beyond estimating overall effectiveness, the study adopts a novel theory-driven framework, coding each intervention according to six foundational theories of loneliness (attachment, social needs, cognitive discrepancy, evolutionary, socio-ecological, and cultural models). This allows for the examination of whether interventions grounded in particular theoretical mechanisms produce stronger and more consistent reductions in loneliness. A key innovation of the project is its explicit consideration of digital context. The review examines whether intervention effectiveness varies by delivery mode (in-person, digital, or hybrid), by national youth social-media prevalence, and by historical period (pre- and post-COVID-19 pandemic). This responds to growing evidence that the experience and structure of loneliness may have shifted alongside widespread smartphone use, social media immersion, and pandemic-related social disruption. Meta-analytic techniques will be used to calculate standardised effect sizes (Hedges’ g) and to conduct multilevel moderator analyses that account for study heterogeneity and statistical dependence. Where quantitative synthesis is not feasible, structured narrative synthesis will be employed. The expected outcomes of this research are threefold. First, it will provide an up-to-date estimate of the effectiveness of loneliness interventions for young people. Second, it will identify which theoretical mechanisms are most strongly associated with positive outcomes, informing the design of more targeted and efficient interventions. Third, it will clarify how digital environments and delivery formats shape intervention efficacy. Collectively, the findings aim to support evidence-informed policy, guide future intervention development, and improve mental health provision for young people in increasingly digital societies.