A Global Phase 3 Study to Evaluate the Safety and Efficacy of Elagolix in Subjects With Moderate to Severe Endometriosis-Associated Pain

Inclusion Criteria:

1. Premenopausal female, between 18 and 49 years of age, inclusive, at the time ofsigning consent.

2. Clinical diagnosis of endometriosis (laparoscopy or laparotomy) performed within 10years of entry into the Washout Period.

3. Agrees to use required birth control methods during the entire length of participationin the study.

4. Subject has a Composite Pelvic Signs and Symptoms Score total score of 6 or greater atScreening with a score of at least 2 for dysmenorrhea AND at least 2 for non-menstrualpelvic pain.

5. Subjects must have at least two regular menstrual cycles with an interval of 24-38days within the Screening Period, prior to Day 1.

Exclusion Criteria:

1. Subject is pregnant or breast feeding or is planning a pregnancy within the next 24months or is less than 6 months postpartum, post-abortion, or post-pregnancy at thetime of entry into the Screening Period.

2. Subject has a history of previous non-response to gonadotropin-releasing hormone (GnRH) agonists, GnRH antagonists, Depot medroxyprogesterone acetate, or aromataseinhibitors as assessed by subject report of no improvement in dysmenorrhea ornon-menstrual pelvic pain.

3. Subject has chronic pelvic pain that is not caused by endometriosis that requireschronic analgesic or other chronic therapy, or that would interfere with theassessment of endometriosis related pain.

4. Clinically significant gynecologic condition identified on Screening transvaginalultrasound or endometrial biopsy.

5. Subject has a history of osteoporosis or other metabolic bone disease.

6. Subject has a current history of undiagnosed abnormal uterine bleeding.