Western medicine, grounded in reductionism as its methodological foundation, has achieved remarkable successes in controlling monogenic infectious diseases, deciphering single‑gene disorders, and advancing surgical techniques. However, as the main battlefield of medicine shifts toward chronic and multimorbid conditions, the deep crisis of this epistemological framework has become fully exposed. This paper applies, for the first time, the eight‑dimensional framework of Prim‑Lex theory to a methodological diagnosis of Western medicine, revealing three nested chains of decoherence: the “physicalist predicament” of reductionist ontology, the “statistical violence” of evidence‑based medicine, and the “domino effect” of multimorbidity. The eight dimensions – Prim‑Unity·Prim‑Fire (reductionist quantification errors in energy metabolism), Two Principles·Yin‑Yang (Yang hyperactivity of antagonistic therapy versus Yin deficiency of systemic repair), Three Realms·GC⁴A (explanatory gaps across molecular, cellular, and organismal scales), Four Phenomena·Four Colors (lack of differentiated attention to the four stages of disease spectrum), Five Elements·Five Models (quintuple coupling disruption from single‑target to polygenic networks, metabolic phenotypes, personalized modeling, and complex system transformation), Six Dimensions·Six Directions (fragmentation of human spatial topology), Seven Luminaires·Seven Rhythms (clinical neglect of circadian rhythms and chronopharmacology), and Eight Trigrams·Eight Information (entropy explosion of clinical and biological data) – collectively demonstrate the collective phase transition of modern medicine from a global coherent state to irreversible decoherence. Network medicine and organicist biology share a deep structural isomorphism with the eight‑dimensional framework at the fundamental logical level, together providing a mathematical countermeasure to the reductionist predicament. This paper demonstrates the scientific validity of the eight‑dimensional coherent‑state criterion as a unified benchmark for evaluating the efficacy and guiding the disciplinary transformation of modern medicine, marking a historic turn from “reductionist hegemony” to “systemic coherence” in clinical medicine.