Study of the Effectiveness of Dydrogesterone in the Treatment of Endometriosis-related Pain

Inclusion Criteria: * Female, ≥18 and ≤45 years of age. * With normal menstrual cycles (according to the International Federation of Gynecology and Obstetrics \[FIGO\]-2018 classification system) in the preceding 6 months before Cycle 0, defined as menstrual frequency ≥24 to ≤38 days, menstrual duration ≤8 days, shortest to longest cycle variation ≤7-9 days, normal flow volume (patient determined) and no intermenstrual bleeding. * Have clinically or surgically diagnosed endometriosis according to routine clinical practice. * Complaints of ERP. * Prescribed treatment with Duphaston® according to the local approved label for treatment of endometriosis 10 mg BID or TID from the 5th to the 25th day of the menstrual period. * Signed informed consent form (ICF). Exclusion Criteria: * With definite diagnosis of adenomyosis confirmed by clinical diagnosis or histopathology. * Routine consumption of analgesics other than for the pain of endometriosis. * Patients receiving hormonal treatment (e.g., dienogest, levonorgestrel releasing intrauterine system, dydrogesterone, etc.) or hormonal contraceptives (including intrauterine devices, contraceptive patches, contraceptive rings, oral contraceptives, etc.) during the previous menstrual cycle prior to Cycle 0. * Ongoing pregnancy. * Menopause or premature ovarian failure. * Had surgery within 3 months before enrollment or have planned surgery during the study. * Any coexisting disease(s) with or without chronic concomitant medication that may affect the assessment of pain intensity at the investigator's judgment. * With any metabolic and genetic diseases that may affect pregnancy and fetus at the investigator's judgment. * With contraindications for dydrogesterone treatment listed in the locally approved label (instructions for the medical use of Duphaston®). * Other conditions that made the patient's participation impossible (based on the investigator's decision). * Fertility treatments requiring assisted reproductive technology. * Patients simultaneous participating in any interventional clinical study during observation period.