Multimorbidity as System Coupling

Multimorbidity is commonly approached as the coexistence of multiple diagnoses within the same individual. This descriptive framework implicitly treats conditions as independent entities and often leads to additive, disease-specific management strategies. This paper reframes multimorbidity as a system-level phenomenon, in which coexisting conditions interact through coupled regulatory processes rather than simple accumulation. From a systems perspective, multimorbidity arises when regulatory domains—such as metabolic, autonomic, inflammatory, or neuroendocrine systems—become dynamically linked, allowing perturbations in one domain to propagate across others. A clear distinction is drawn between comorbidity and multimorbidity: comorbidity describes coexistence, whereas multimorbidity describes interaction. Clinical instability, treatment intolerance, and unpredictable responses are interpreted as consequences of coupling strength, loss of regulatory separability, and timing sensitivity rather than disease count alone. This work presents a clinical interpretation framework within Dynamic Medicine, shifting focus from managing individual diagnoses to understanding and stabilizing interacting regulatory systems. No new experimental or clinical data are introduced. Conceptual clinical framework; no new experimental or clinical data.