Toward a transdiagnostic modifier for clinically significant loneliness in psychiatry: a conceptual mini review

Loneliness, the feeling that arises from the subjective perception of inadequate social connection, is increasingly recognized as a significant and modifiable determinant of health with effects spanning mental, cognitive, and physical domains. Despite a robust evidence base linking loneliness to adverse mental and physical health outcomes, it remains insufficiently integrated into psychiatric assessment and diagnostic frameworks, limiting its visibility in a patient's clinical picture and treatment planning. This paper proposes reconceptualizing clinically significant loneliness as a transdiagnostic diagnostic modifier within psychiatric practice. Loneliness is positioned as a multisystem exposure operating across diagnostic categories through shared neurobiological and psychosocial pathways. From a translational science perspective, this reconceptualization offers a pragmatic strategy to bridge the gap between evidence and practice by embedding a clinically actionable construct into routine care. Importantly, assessing loneliness alongside psychiatric diagnoses enhances understanding of patients' lived experiences, providing critical contextual insight into how symptoms are experienced, maintained, and treated. Incorporating loneliness as a modifier supports improved risk stratification, treatment planning, and care coordination while preserving the contextual nature of the experience. Integrating loneliness into psychiatric assessment represents a feasible and scalable step toward more comprehensive, person-centered care.