Study Of Oral Elagolix Tablets In Combination With Combined Oral Contraceptive Capsules/Tablets To Assess Dysmenorrhea Response In Adult Female Participants With Endometriosis And Associated Moderate To Severe Pain

Inclusion Criteria: * Documented surgical confirmation of endometriosis and associated moderate to severe pain. * Participants must agree to use dual non-hormonal methods of contraception consistently during washout (if applicable), screening, and 3-month double-blind placebo-controlled treatment periods of the study. * Participant, in the investigator's opinion must be an appropriate candidate to receive combined oral contraceptives (COCs). Exclusion Criteria: * Pregnant or breastfeeding or planning a pregnancy until completion of the study. * Surgical history of hysterectomy or bilateral oophorectomy. * Participant has osteoporosis or other metabolic bone disease or clinically significant gynecological findings from Screening. * Participant has any other active chronic pain condition that would interfere with their assessment of endometriosis-related pain.