Endometrin (progesterone vaginal insert) is a specially formulated vaginal tablet that contains the female hormone progesterone, which is one of the hormones essential for preparation of the uterus for implantation and maintenance of a pregnancy. Once the tablet is inserted into the vagina, it quickly dissolves and is available to be absorbed into the circulation to be taken to the uterus.

Side effects reported by women who used Endometrin in clinical studies reported the following side effect more than 2% of the time: uterine spasm (3-4%) vaginal bleeding (3%). Vaginal irritation, itching, burning, rash or swelling were reported less than 2% of the time.