Randomized controlled trials of major oral traditional Chinese medicine preparations for postherpetic neuralgia: an evidence map

Objective To identify and synthesize randomized controlled trials (RCTs) of oral traditional Chinese medicine (TCM) for postherpetic neuralgia (PHN), map the volume, methodological quality, and evidence distribution, identify evidence gaps, and inform future research. Methods We systematically searched PubMed, Embase, the Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang Data, VIP Database, the Chinese Clinical Trial Registry (ChiCTR), and China Biomedical Literature Database (CBM). RCTs published from database inception to 1 August 2025 were included. The evidence was summarized using evidence maps and narrative synthesis. Risk of bias in the included RCTs was assessed using the Cochrane Risk of Bias tool (RoB 1.0). Results A total of 357 RCTs were included, most were small studies with sample sizes ranging from 50 to 100 participants. Most studies reported diagnostic criteria and inclusion/exclusion criteria, however, limited attention was paid to TCM syndrome differentiation and its standardization. The main outcomes were pain degree, clinical effective rate, adverse reactions, sleep quality, negative emotions, and quality of life, however, outcomes such as recurrence and TCM syndrome scores were infrequently reported. Overall methodological quality was low, as assessed using the RoB 1.0. Conclusion Although many included studies reported favourable findings, the formulas and preparations differed substantially in composition, and high-quality evidence remains limited. Future trials should better incorporate key features of TCM (e.g., syndrome differentiation), use standardized and clinically meaningful outcome measures, and strengthen trial design and reporting to reduce risk of bias and improve the credibility of evidence. Systematic Review Registration URL: https://www.crd.york.ac.uk/PROSPERO/view/CRD420251110786 , identifier CRD420251110786.