Menstruation 9 days early and very light may be caused by hyperthyroidism, polycystic ovary syndrome, uterine adhesions and other diseases. 1. Hyperthyroidism: the cause may be related to the increase of thyroid hormone, intake of large amount of iodine-containing food or drugs. Patients may have symptoms such as tachycardia, fatigue, excessive sweating, etc. Female patients may have changes in menstrual cycle and scanty menstrual flow. 2. Polycystic ovary syndrome: the cause of the disease is not clear, and may be related to genetic and environmental factors. Patients show that there is no regularity in menstrual cycle and menstrual flow, and they may have low menstrual flow, scanty menstruation and amenorrhea. 3. Uterine adhesion: the etiology may be related to endometrial trauma, low estrogen level, heredity and uterine malformation. Patients may experience reduced menstruation and cyclic abdominal pain. There are more causes of menstrual disorders, and it is recommended to go to regular hospitals for examination to clarify the causes.