Placebo-controlled Proof of Concept Study of Epelsiban in Women With Adenomyosis

Inclusion Criteria: * Eighteen to 55 years of age, inclusive * Pre-menopausal with a history of regular menstrual cycles every 21-35 days and without intermenstrual bleeding heavier than spotting and staining. * Females with adenomyosis confirmed on magnetic resonance imaging (MRI), - Females with heavy menstrual bleeding . * Willing and able to collect all menstrual cycle by-products for each cycle from screening to follow up. * Not pregnant as confirmed by a negative serum human chorionic gonadotropin Exclusion Criteria: * A female subject will not be eligible for inclusion in this study if any of the following criteria apply: * Abnormal gynecological examination other than adenomyosis and/or breast examination requiring intervention within six months of study start * Abnormal endometrial biopsy within six months of starting study treatment. * History of an endometrial ablation within 12 months of starting study treatment. * Uterine artery embolization within six months of starting study treatment. * Prior major uterine procedures or any other significant uterine abnormalities on MRI (previous caesarean section, dilation and curettage, and diagnostic hysteroscopy are permitted). * Confirmed rectovaginal endometriosis in women who have undergone a prior laparoscopy. * Active pelvic infection or current use of an intrauterine device within three months of screening. * Women with a history of transfusion for heavy menstrual bleeding within the past 2 years or history of postpartum hemorrhage. * Any uterine dimension \>20 centimeter (cm). * Other major causes of heavy menstrual bleeding - * Use within 3 months or anticipated use of medications that modify reproductive function * Use or anticipated use of the following drugs: anticoagulants aminocaproic acid ,or any other medications that affect menstrual bleeding such as tranexamic acid. * Use of daily opioid pain medications other than with menses. * Hemoglobin \<8 grams (g)/deciliter. * History of bleeding disorder or known presence of acquired or inherited thrombophilia, (sickle cell trait individuals are not excluded).