When a woman is monitored for ovulation and ovulation disorders are found, ovulation promotion therapy can be administered, usually starting on the fourth day of menstruation. There are two commonly used drugs: one is called clomiphene; the other is called letrozole. There is a difference in the mechanism of ovulation promotion between the two drugs: clomiphene is mainly an estrogen receptor antagonist, and letrozole is mainly an aromatase inhibitor. Both drugs have the same principle of action and purpose, and address common ovulation disorders, such as polycystic ovary syndrome, unruptured follicle luteinization syndrome, and follicular atresia.