Effectiveness and safety of light therapy for treating primary dysmenorrhea: A systematic review and meta-analysis of randomized controlled trials

Objective

Primary dysmenorrhea, defined as painful menstrual cramps without identifiable pelvic pathology, is a prevalent gynecological condition that significantly impacts quality of life. Emerging evidence suggests that light-based therapies, including low-level light therapy (LLLT) and high-intensity light therapy (HILT), may offer a non-pharmacological approach to managing menstrual pain. This systematic review aimed to assess the effectiveness and safety of light therapy in individuals with primary dysmenorrhea.

Methods

For this systematic review and meta-analysis, we searched twelve electronic databases, including PubMed, Cochrane Library, Embase, Allied and Complementary Medicine Database (AMED), APA PsycINFO, CINAHL Complete, Web of Science, China National Knowledge Infrastructure (CNKI), Chinese Scientific Journals Database (VIP), WanFang Data, Research Information Sharing Service (RISS), and Oriental Medicine Advanced Searching Integrated System (OASIS) to identify randomized controlled trials (RCTs) evaluating the effectiveness of light therapy for primary dysmenorrhea. The search was conducted up to February 4, 2025. Two reviewers independently assessed articles for eligibility and extracted data. Disagreements were resolved through discussion. Critical outcomes were pain scales such as the Visual Analog Scale (VAS) or Numeric Rating Scale (NRS). Risk of bias was assessed using the Cochrane Risk of Bias Tool (RoB 2), and meta-analyses were conducted using RevMan software. The study protocol was registered in PROSPERO (CRD420250655437). Available from https://www.crd.york.ac.uk/PROSPERO/view/CRD420250655437.

Setting

Twelve studies involving 645 participants met the inclusion criteria, highlighting the potential therapeutic role of light therapy.

Results

Interventions primarily involved LLLT (n = 6), with some using HILT (n = 2) or polarized light (n = 1). Meta-analysis of three RCTs showed a statistically significant reduction in pain after 12 weeks of LLLT compared to sham treatment (n = 150, mean difference (MD) = -4.02, 95 % confidence interval (CI): −7.21 to −0.82; p = 0.01). Similarly, LLLT also demonstrated greater pain reduction compared to oral contraceptives after 12 weeks (n = 156, MD = 0.91, 95 % CI: 0.49–1.33, p < 0.0001). Most studies were assessed as having some concerns regarding risk of bias. Reported adverse effects were minor and transient, with no serious adverse events noted.

Conclusion

Light therapy, particularly LLLT, may represent a safe and effective non-pharmacological intervention for the management of primary dysmenorrhea. Despite promising results, variations in treatment protocols contributed to heterogeneity and hindered identification of optimal parameters. Limited trial numbers and regional concentration also reduce generalizability. Further high-quality, large-scale RCTs with standardized treatment protocols are needed to confirm clinical efficacy and define optimal therapeutic parameters.