Low menstrual flow in a 40-year-old woman is considered abnormal, as 40 years old is still particularly far from menopause. According to the basic theory of Chinese medicine, low menstrual flow is mostly related to blood deficiency, kidney deficiency and blood stasis, among which blood deficiency is the most common cause. If low menstrual flow is accompanied by pale or yellowish face, palpitation, panic, insomnia, dreaminess, pale lips and tongue, etc., it is mostly considered to be caused by blood deficiency. If it is accompanied by weakness of the waist and knees, tinnitus and deafness, etc., it is mostly considered to be caused by deficiency of essence and blood in the kidneys. If the menstrual flow is small but purple in color, accompanied by blood clots and painful menstruation during menstruation, it is most often considered to be related to blood stasis.