There are more reasons for long dark brown menstrual period, which may be related to the body’s luteal insufficiency, endometrial adhesion and abnormal ovarian function. 1. Luteal insufficiency: long dark-brown menstrual period may be related to insufficient secretion of the corpus luteum formed after ovulation of the ovary or luteal dysfunction, which may cause the body to have long dark-brown menstrual period. 2. Endometrial adhesion: If there is endometrial adhesion in the body, it may cause the body to have the symptoms of long dark brown menstrual period, which may make it difficult for menstrual blood to flow out. 3. Abnormal ovarian function: If the body has ovarian function decline, polycystic ovary syndrome, etc., it may cause the body’s hormone level to change, which may lead to abnormal menstrual period and dark brown color of menstrual blood. There may also be other reasons for long dark brown menstrual periods, so we suggest that you go to the hospital in time, complete the examination to determine the cause of the disease, and then give targeted treatment or therapy under the guidance of a professional doctor.