Oral Gonadotropin-Releasing Hormone Antagonists for the Treatment of Endometriosis-Associated Pain: A Systematic Review and Meta-Analysis

STUDY OBJECTIVE: To evaluate the efficacy of oral gonadotropin-releasing hormone (GnRH) antagonists vs placebo for treatment of endometriosis-associated pain and to compare individual antagonists indirectly for dysmenorrhea and non-menstrual pelvic pain. DESIGN: Systematic review and meta-analysis of phase 3 randomized, double-blind, placebo-controlled trials of oral GnRH antagonists in people with moderate-to-severe endometriosis-associated pain, with dual screening, standardized data extraction, and risk of bias assessment using the Cochrane Risk of Bias 2 tool. SETTING: Multicenter phase 3 clinical trials conducted in outpatient gynecology and reproductive health settings across North America, Europe, and other international sites, identified through electronic databases and trial registries from inception through October 2025. PATIENTS: A total of 2060 participants with surgically or imaging-diagnosed endometriosis and moderate-to-severe baseline pain, with mean ages of 31 to 35 years, enrolled in five phase 3 trials (ELARIS, SPIRIT 1 and 2, and EDELWEISS-3). INTERVENTIONS: The included trials evaluated three oral GnRH antagonist regimens: elagolix 200 mg twice daily without add‑back, relugolix 40 mg once daily combination therapy, and linzagolix 200 mg once daily with add-back. Add-back and combination therapy were defined as co‑administration of estradiol 1 mg and norethindrone acetate 0.5 mg once daily. Each regimen was compared with a matching placebo for treatment durations up to 24 weeks. MEASUREMENTS AND MAIN RESULTS: Primary outcomes were binary responder rates for dysmenorrhea and non-menstrual pelvic pain, defined by prespecified reductions in daily pain scores with stable or reduced analgesic use. Fixed-effects meta-analysis with inverse-variance weighting yielded a pooled risk ratio of 3.06 (95% CI, 2.76-3.39; p <.001) and a number needed to treat (NNT) of 2 (95% CI, 2-3) for dysmenorrhea responders, and a pooled risk ratio of 1.53 (95% CI, 1.40-1.67; p <.001) and NNT of 5 (95% CI, 4-7) for non-menstrual pelvic pain responders, with no statistical heterogeneity (I² = 0%) for either outcome. Drug-level pooled risk ratios for dysmenorrhea were 3.49 (95% CI, 2.93-4.16) for elagolix 200 mg twice daily, 3.11 (95% CI, 2.32-4.17) for linzagolix 200 mg with add-back, and 2.61 (95% CI, 2.22-3.07) for relugolix combination therapy; corresponding pooled risk ratios for non-menstrual pelvic pain were 1.54 (95% CI, 1.31-1.80), 1.52 (95% CI, 1.15-2.01), and 1.52 (95% CI, 1.32-1.74), respectively. Bucher-adjusted indirect comparisons did not show robust differences in efficacy between agents for either pain domain, although elagolix was associated with a statistically significant higher dysmenorrhea response than relugolix combination therapy (risk ratio, 1.34; 95% CI, 1.05-1.70; p = .017). CONCLUSION: Oral GnRH antagonists provide consistent, significant, and clinically meaningful reductions in dysmenorrhea and non-menstrual pelvic pain compared with placebo, with low heterogeneity across trials and similar efficacy among elagolix, relugolix combination therapy, and linzagolix with add-back, supporting their use as effective second-line therapy for endometriosis-associated pain.