When you have a period, it is bleeding caused by the shedding of the endometrium. When the endometrium sheds and causes bleeding, this blood will accumulate in the uterine cavity, and when the accumulation reaches a certain amount, it will stimulate the uterus to cause contraction, so that the menstrual blood in the uterine cavity will be discharged outside the vagina, so it is normal for menstrual blood to be discharged only when there is uterine contraction at the time of menstruation. In clinical practice, when the endometrium is shed, a large amount of prostaglandin is secreted, so it will lead to severe contraction of the smooth muscle of the uterus, so that the patient will feel pain in the lower abdomen, and the clinical manifestation is dysmenorrhea, which requires certain drug intervention, such as oral Tianqi dysmenorrhea capsules, or hot compresses on the lower abdomen can relieve dysmenorrhea.