Comparative post-marketing reporting signals of elagolix and myfembree in endometriosis: a FAERS pharmacovigilance study.

BACKGROUND: Elagolix and Myfembree are gonadotropin-releasing hormone (GnRH)-pathway therapies used for endometriosis, but their post-marketing safety reporting patterns remain incompletely characterized. Because spontaneous reporting databases are susceptible to reporting bias and differential market exposure, comparative analyses require cautious interpretation.

METHODS: We analyzed quarterly data from the FDA Adverse Event Reporting System (FAERS) from 2015Q3 to 2026Q1. Deduplicated female reports with endometriosis-related indications were identified and classified as elagolix, Myfembree, or other endometriosis-related reports. The primary analysis consisted of drug-specific case-noncase disproportionality analyses for elagolix and Myfembree separately within the female endometriosis reporting background. A direct elagolix-versus-Myfembree head-to-head analysis was performed as a secondary analysis. Reporting odds ratios (RORs), proportional reporting ratios (PRRs), and information components (ICs) were calculated at the preferred term (PT) level. Sensitivity analyses included serious-report-only, healthcare-professional-only, physician-only, complete-age, reporter-type-stratified, overlapping-market-period, and bootstrap analyses.

RESULTS: A total of 4,428 deduplicated female endometriosis-related reports were included, comprising 1,744 elagolix reports, 280 Myfembree reports, and 2,404 other endometriosis-related reports. Serious reports accounted for 31.2% of elagolix reports and 26.8% of Myfembree reports. In drug-specific case-noncase analyses, elagolix showed robust disproportionality signals for hot flush, night sweats, and suicidal ideation. Myfembree showed distinct reporting signals for reproductive and bleeding-related PTs, including heavy menstrual bleeding and intermenstrual bleeding. In the secondary head-to-head analysis, selected PTs including hot flush, nausea, headache, depression, arthralgia, and suicidal ideation showed higher reporting signals for elagolix, whereas alopecia showed a lower reporting signal for elagolix. Sensitivity analyses using alternative algorithms, reporter-type restrictions, overlapping-market-period restriction, complete-age restriction, and bootstrap validation generally supported the direction of the main selected reporting patterns, although some estimates were limited by small cell counts.

CONCLUSIONS: Elagolix and Myfembree showed distinct post-marketing reporting signal profiles among female endometriosis-related FAERS reports. Elagolix was characterized mainly by vasomotor and selected neuropsychiatric reporting signals, whereas Myfembree was characterized mainly by reproductive and bleeding-related reporting signals. These findings represent hypothesis-generating reporting differences rather than clinical incidence rates or causal risk estimates. Further pharmacoepidemiologic studies with denominator data and adjustment for patient-level confounding are needed to clarify comparative safety profiles.