Efficacy and Safety Study of Elagolix Versus Placebo or Leuprorelin Acetate in Endometriosis

Inclusion Criteria * Female, aged 18 to 45 years, inclusive * Have moderate to severe pelvic pain due to endometriosis * Have been surgically (laparoscopy) diagnosed with endometriosis within the last 5 years and have recurrent or persistent endometriosis symptoms * Have regular menstrual cycle (23-33 day) * Agree to use two forms of non-hormonal contraception during the study Exclusion Criteria: * Received a Gonadotropin-releasing hormone (GnRH) agonist, GnRH antagonist, danazol, or have received any of these agents within 6 months of the start of screening. * Received subcutaneous medroxyprogesterone acetate (DMPA-SC) or intramuscular (i.m.) medroxyprogesterone acetate (DMPA-IM), or have received either of these agents within 3 months of the start of screening. * Are currently using hormonal contraception or other forms of hormonal therapy or received such treatment within the last month * Have had surgery for endometriosis within the last month * Are using systemic steroids on a chronic or regular basis within 3 months * Have uterine fibroids or other pelvic lesions ≥ 3 cm in diameter * Have had a hysterectomy or oophorectomy * Have pelvic pain that is not caused by endometriosis * Have unstable medical condition or chronic disease * Have been pregnant within the last 6 months and is currently breast feeding