PURPOSE: Limitated studies have reported the efficacy of GnRH antagonist on 
endometriosis symptoms. The aim of our study was to review all available trials 
to investigate the medical treatment of endometriosis with only GnRH 
antagonists, with special attention to pharmacodynamic activity, safety, and 
efficacy.
METHODS: Pub Med and Sciencedirect database were searched using terms of 
"endometriosis treatment", "GnRH antagonist", and "Elagolix". The search was 
limited to clinical studies published in English. Title and abstract were 
screened to identify relevant articles.
RESULTS: Five studies covering use of GnRH antagonist were found. A phase 1 
study evaluated the safety, pharmacokinetics, and inhibitory effects on 
gonadotropins and estradiol of single dose and 7 day elagolix administration to 
healthy premenopausal women; two phase II studies evaluated efficacy in patient 
with endometriosis. Moreover, there are two Phase III clinical trials just 
completed.
CONCLUSION: GnRH antagonists may have the advantage of oral administration and 
lower incidence of adverse events. Currently, only Phase II studies have been 
published demonstrating promising results in terms of efficacy, safety, and 
tolerability. From the results of the phase III studies, elagolix may become a 
valuable addition to the armamentarium of pharmacological agents to treat 
endometriosis-related pain.