Progesterone is a natural progestogen secreted by the corpus luteum of the ovary. It has a significant morphological effect on the endometrium stimulated by estrogen in the body and is necessary to maintain pregnancy. 1. In the late menstrual cycle, it causes the growth of glands in the uterine mucosa, uterine congestion, and endometrial thickening to prepare for the implantation of the fertilized egg. After the fertilized egg is implanted, it causes the placenta to form, reduces the excitability of the pregnant uterus, inhibits its activity, and allows the fetus to grow safely. 2. Under the combined action of estrogen, it promotes full breast development to prepare for milk production. 3. It closes the cervical opening, reduces and thickens the mucus, making it difficult for sperm to penetrate; in large doses, it inhibits the secretion of pituitary gonadotropin through negative feedback on the hypothalamus, producing an inhibitory effect on ovulation. 4. It is rapidly absorbed through the vaginal mucosa, and the blood concentration reaches a peak after 2 to 6 hours. It is mainly used clinically for habitual abortion, dysmenorrhea, excessive menstrual bleeding or metrorrhagia, amenorrhea, etc. Oral high doses are also used for conditions caused by progesterone deficiency, such as premenstrual syndrome, menstrual disorders caused by cessation of ovulation, benign breast disease, premenopause and menopause, etc.