This study is an international phase 3 open-label, single-arm, long-term efficacy and safety extension study that will enroll eligible participants who have completed their participation in one of the phase 3 randomized, double-blind, placebo-controlled parent studies, MVT-601-3101 (SPIRIT 1 - NCT03204318) or MVT-601-3102 (SPIRIT 2 - NCT03204331). All participants will receive relugolix 40 mg orally once daily co-administered with low-dose E2 (1.0 mg) and NETA (0.5 mg) for 80 weeks.~Approximately 800 women with endometriosis-associated pain will be enrolled, after having completed a 24-week treatment period in one of the parent studies. The objectives of the study are to evaluate long-term efficacy and safety through up to 104 weeks of treatment (including treatment during the parent study) of relugolix co-administered with low-dose E2/NETA.~Baseline procedures for this extension study will be performed on the same day as the Week 24 Visit of the parent study. This visit, referred to as the Week 24/Baseline Visit, will be defined as the date of completion of the last Week 24 procedure in the parent study. Participants will have received their last dose of study drug in the parent study on the day prior to the Week 24/Baseline Visit and will receive their first dose of study drug for this extension study in the clinic after the participant is determined to be eligible for this extension study and has provided informed consent to participate. The administration of the first dose of study drug for MVT-601-3103 will define enrollment into this study. Study participants will then take the open-label study treatment orally, once daily for 80 weeks.
The purpose of this study is to evaluate the long-term efficacy and safety of relugolix 40 milligram (mg) once daily co-administered with low-dose estradiol (E2) and norethindrone acetate (NETA) for up to 104 weeks on endometriosis-associated pain in participants who previously completed a 24-week treatment period in one of the parent studies (MVT-601-3101 or MVT-601-3102).