Transcutaneous electrical nerve stimulation in the relief of primary dysmenorrhea: a systematic review and meta-analysis.

OBJECTIVE: To synthesize evidence on TENS efficacy for primary dysmenorrhea, providing quantitative meta-analysis of pain intensity, exploratory subgroup analyses on electrode placement, and systematic RoB 2 assessment, addressing gaps from previous qualitative reviews. METHOD: Systematic search across PubMed, VHL, Web of Science, Embase, LILACS, PEDro, and gray literature, without restrictions. RoB 2 was applied independently by two reviewers. Primary outcome: pain intensity. Meta-analysis used RevMan 5.4.1. RESULTS: Eight studies included from 1,018 records. TENS significantly reduced pain (SMD = -1.85; 95% CI -2.90 to -0.79; p < 0.001), with high heterogeneity (I2 = 94%). Subgroup analyses showed significant effects regardless of application site.  . CONCLUSION: This meta-analysis quantifies TENS analgesic effect for primary dysmenorrhea, suggesting pain reduction irrespective of electrode placement. However, very high heterogeneity, moderate-to-high risk of bias, wide parameter variability, small samples, and imprecise subgroup estimates limit certainty. TENS appears safe (no serious adverse events), but underreporting prevents firm conclusions. Standardized protocols and high-quality, low-bias trials are needed. Certainty is likely low per GRADE considerations. PROTOCOL REGISTRATION: www.crd.york.ac.uk/prospero identifier is CRD42024540314.