A 28-year-old patient complains of profuse, painful and prolonged menstruation. Before and after the menstrual period there is spotting lasting for 4-6 days. Vaginal examination reveals that the uterus is enlarged corresponding to 5-6 weeks of pregnancy, has limited mobility, is painful. Appendages are not palpable. On the 15th day of the menstrual cycle, the uterus was of normal size, painless. On account of stated problems and objective examination the patient has been diagnosed with internal endometriosis. Which drug should be used for the efective treatment of this patient?