A Phase 3 Study to Confirm the Efficacy and Safety of Linzagolix to Treat Endometriosis-associated Pain

Key Inclusion Criteria: The subject must have: * Her most recent surgical and - if available - histological diagnosis of pelvic endometriosis up to 10 years before screening. * Moderate to severe endometriosis-associated pain during the screening period. * Regular menstrual cycles. * BMI ≥ 18 kg/m2 at the screening visit. Key Exclusion Criteria: The subject will be excluded if she: * Is pregnant or breast feeding or is planning a pregnancy within the duration of the treatment period of the study. * Is less than 6 months postpartum or 3 months postabortion/ miscarriage at the time of entry into the screening period. * Has had a surgical history of any major abdominal surgery within 6 months or any interventional surgery for endometriosis performed within a period of 2 months before screening. * Did not respond to prior treatment with GnRH agonists or GnRH antagonists for endometriosis. * Has a history of, or known, osteoporosis or other metabolic bone disease. * Has chronic pelvic pain that is not caused by endometriosis and requires chronic analgesic or other chronic therapy which would interfere with the assessment of endometriosis-associated pain.