Menorrhagia is the external manifestation of pathophysiological changes in the female body caused by a variety of diseases, and it is a clinical symptom rather than a disease. It can be classified as physiological or pathological according to its cause. Physiological amenorrhea is the absence of menstruation during pregnancy, lactation and after menopause. Pathological amenorrhea is caused directly or indirectly by functional or organic lesions of the central nervous-hypothalamic-pituitary-ovarian axis and various parts of the target organ, the uterus. Hypothalamic amenorrhea Hypothalamic amenorrhea is amenorrhea caused by various functional and organic disorders of the hypothalamus. This type of amenorrhea is characterized by defective or insufficient synthesis and secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus resulting in low function of pituitary gonadotropins (Gn), i.e. follicle stimulating hormone (FSH) and luteinizing hormone (LH), and can be classified by etiology into 3 major categories: functional (e.g. stress, motor, neurological, nutrition-related, etc.), genetic defects or organic, and pharmacological. Pituitary amenorrhea Pituitary amenorrhea is caused by a decrease in Gn secretion due to pituitary lesions. The main causes include: pituitary tumors, empty saddle syndrome, congenital pituitary lesions, Sheehan syndrome, etc. Ovarian amenorrhea Ovarian amenorrhea is caused by the ovaries themselves. Gn levels are elevated in ovarian amenorrhea, which is classified as congenital gonadal dysgenesis (including chromosomally normal and chromosomally abnormal types), enzyme defects, ovarian resistance syndrome and acquired ovarian hypofunction due to various causes. Uterine amenorrhea There are two types of uterine amenorrhea: congenital and acquired. The causes of congenital uterine amenorrhea include MRKH syndrome and androgen insensitivity syndrome with abnormal development of the Mullerian ducts; the causes of acquired uterine amenorrhea include amenorrhea caused by infection and trauma leading to uterine adhesions. In contrast, abnormal developmental amenorrhea of the lower genital tract includes cervical atresia, transverse vaginal septum, vaginal atresia and hymenal atresia. Other causes In addition to the above lesions, diseases with elevated androgen levels, such as polycystic ovary syndrome (PCOS), congenital adrenocortical hyperplasia (CAH), androgen-secreting tumors and follicular membrane cell proliferation disorders, may also cause amenorrhea. Other pathways involved in the regulation of hormonal changes in the female body can also cause amenorrhea, such as thyroid or adrenal gland generator or functional disorders. In conclusion, menorrhagia occurs due to a variety of complex causes. Women should pay attention to menstrual changes and seek medical attention in case of amenorrhea.