Loneliness in adolescents and youth with bipolar disorder: a scoping review.

Introduction: Bipolar disorder (BD) commonly emerges in adolescence, a period marked by heightened mood lability and shifting social roles that may amplify interpersonal stressors and functional risk. Loneliness and social isolation are transdiagnostic, developmentally salient constructs associated with psychiatric morbidity and physiological dysregulation, yet their relevance to youth BD has not been comprehensively summarized. This review synthesizes evidence on loneliness and social isolation in adolescents and youth with BD. Methods: We systematically searched PubMed, PsycINFO, Embase, and CINAHL from inception to July 2025 using terms related to BD, loneliness/social isolation, and adolescents/youth. Peer-reviewed studies were eligible (no language/date restrictions) if they included participants with a formal diagnosis of BD and measured loneliness and/or social isolation. Of 514 records screened, six studies met inclusion criteria. Methods followed the PCC framework, JBI Reviewer's Manual, and PRISMA-ScR guidelines. Results: Six studies (N = 522) included adolescents and young adults with BD. Across heterogeneous designs, loneliness and/or social isolation were repeatedly associated with BD-relevant outcomes, including diagnostic group differences, altered neural responses to social exclusion, and temporal proximity to mood episodes. Social isolation was generally related to poorer psychosocial functioning. Conclusion: Available evidence suggests that loneliness and social isolation are meaningfully related to clinical and functional correlates in youth BD and may help distinguish BD from comparison groups, although causal and temporal inferences remain limited. Longitudinal and mechanistic studies are needed to clarify directionality and pathways (e.g., mood, cognition, stress biology). Clinically, routine assessment and interventions targeting loneliness/social isolation may be warranted.