Safety Profile of Thread-Embedding Acupuncture: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background/Objectives: Thread-embedding acupuncture (TEA) involves the implantation of suture threads into therapeutic points for sustained stimulation; however, its safety evidence remains limited. This systematic review and meta-analysis evaluated adverse events (AEs) associated with TEA to establish its safety profile. Methods: Ten databases were searched up to April 5, 2026 for randomized controlled trials (RCTs) of TEA. Reported AEs were standardized using MedDRA terminology, WHO-UMC causality criteria, and CTCAE version 5.0. Pooled incidence proportions were estimated using generalized linear mixed models, and risk ratios (RRs) were pooled using random-effects models with 95% confidence intervals (CIs). Results: Of the 90 RCTs included, most were conducted in China (81, 90.0%). For TEA monotherapy, pooled AE incidence proportion was 3% (95% CI: 2-7%; I² = 53.7%). Local AEs were most common (111, 5.9%), followed by systemic (5, 0.3%) and other AEs (2, 0.1%). Among 118 participants with AEs, most were classified as Grade 1 (95, 80.5%), with Grade 2 (8, 6.8%) and unassessable cases (15, 12.7%). In comparative analyses, TEA showed no significant increase in AE risk versus sham TEA (RR: 1.15, 95% CI: 0.83-1.60), acupuncture (RR: 0.97, 95% CI: 0.64-1.49), or conventional medicine (RR: 0.28, 95% CI: 0.18-0.45). Only one serious TEA-related AE was reported among 1697 participants (0.06%); the withdrawal rate due to TEA-related AEs was 0.36% (9/2524). Conclusions: TEA demonstrated a favorable safety profile when used alone or as an add-on therapy, with most AEs mild and transient. However, inconsistencies in AE definitions and reporting highlight the need for standardized terminology and more rigorous safety evaluation in future studies.