Heat therapy for primary dysmenorrhea: a systematic review and meta-analysis

Aim: Primary dysmenorrhea is highly prevalent and often suboptimally managed, as non-steroidal anti-inflammatory drugs (NSAIDs) fail to provide analgesia in 18% of women. This review therefore aims to evaluate the efficacy and safety of heat therapy-a widely used self-care method-for both preventing and acutely treating primary dysmenorrhea. Methods: We searched seven databases (CENTRAL, PubMed, Web of Science, EMBASE, CNKI, VIP, Wanfang) from inception to October 28, 2024 and updated to August 03, 2025. Pairs of reviewers independently screened records, extracted data, and assessed risk of bias using a modified Cochrane RoB 1.0 tool. Random-effects meta-analyses were performed for pain intensity (converted to 10-cm VAS) and adverse events. Evidence certainty was graded via GRADE (Grading of Recommendations, Assessment, Development, and Evaluations). Results: We screened 2,733 citations and included 57 RCTs (involving 5,359 female participants). When compared with no treatment, heat therapy may reduce pain intensity to a greater extent after 3 months (25 RCTs, 2,393 females, WMD -1.85 cm, 95% CI -2.29 to -1.41 cm, RD 21%); it may lead to a greater reduction within 24 h of treatment (3 RCTs, 248 females; WMD -3.52 cm, 95% CI -5.01 to -2.02 cm, RD 45%). When compared to NSAIDs, heat therapy may provide comparable or slightly superior pain relief after 3 months of treatment (22 RCTs, 1,938 females, WMD -1.10 cm, 95% CI -1.51 to -0.70 cm, RD 4%), or within 24 h of treatment (2 RCTs, 167 females, WMD -1.50 cm, 95% CI -2.86 to -0.15 cm, RD 16%). For the safety assessment, heat therapy probably reduced the risk of adverse effects compared with NSAIDs (8 RCTs, 728 females, RR 0.30, 95% CI 0.15-0.59). Conclusions: Compared to no treatment, heat therapy is likely to reduce pain intensity both during prophylaxis and acute episodes. When compared to NSAIDs, heat therapy may achieve comparable analgesic efficacy while exhibiting a superior safety profile. Systematic review registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD420251050944, identifier CRD420251050944.