Regestrone CR 10 mg Tablet belongs to the class of medicines called progestogens used to treat heavy, painful, or irregular periods, premenstrual syndrome (PMS), and endometriosis. Additionally, Regestrone CR 10 mg Tablet may be used in the treatment of breast cancer. Endometriosis is a disorder in which the uterus's tissue lining (endometrium) grows on the ovaries, bowel, or tissues lining the pelvis. The most common symptom is pelvic pain.