Progesterone is a hormone which involved in the menstrual cycle in women, particularly in helping to build up the rich tissue layer in the uterus in preparation for an implanted embryo. Progestin is a term which is used to cover a group of synthetic drugs which have progesterone-like effects.

Progestin is usually prescribed in combination with estrogen in hormone replacement therapy, since estrogen replacement alone is associated with a high risk of uterine cancer. Progestin (or progesterone) is also used to treat menstrual disorders, such as abnormal bleeding).