Chinese herbal formulas for Hashimoto's thyroiditis based on the thyroid-gut axis: multitarget synergistic mechanisms and boundaries of evidence.

Background: Hashimoto's thyroiditis (HT) is a common autoimmune thyroid disease. Although levothyroxine replacement therapy can correct hypothyroidism, it does not directly reverse the autoimmune process. The thyroid-gut axis provides a mechanistic framework for understanding how intestinal barrier injury, microbial dysbiosis, disrupted immune homeostasis, and endocrine disturbance jointly contribute to HT. Objective: This review systematically summarizes current evidence on Chinese herbal formulas that intervene in HT through the thyroid-gut axis and proposes a target-combination-based mechanistic framework. Methods: Original studies published from 2015 to 2025 were searched in CNKI, PubMed, Embase, and the Cochrane Library. Thirty-three records were initially identified, and eight studies on eligible Chinese herbal formulas were ultimately included. Results: The included formulas covered four pathological nodes: intestinal barrier repair (A), gut microbiota remodeling (B), immune homeostasis reconstruction (C), and endocrine function restoration (D). The observed target combinations included A+C, B+C, B+C+D, and A+B+C+D. On this basis, we propose a four-level linkage model to integrate the available evidence. Conclusion: Chinese herbal formulas may modulate HT pathology through multitarget regulation of the thyroid-gut axis. However, the current evidence is mainly derived from heterogeneous preclinical animal studies and remains largely correlative. Future studies should include randomized controlled clinical trials, causal microbiome experiments, standardized outcome assessment, safety evaluation, and pharmacokinetic investigation.