Endometrin is a vaginal insert containing progesterone 100mg. Progesterone is a female hormone important for ovulation and menstruation. Progesterone causes changes in the lining of the uterus, making it easier for a fertilized egg to attach to the uterus at the beginning of pregnancy. Endometrin helps the body maintain the pregnancy. PLEASE NOTE: Outside the USA, Endometrin is sold with a reusable applicator. Should you prefer the convenience of disposable applicators for each insert you will need to purchase Endometrin from a pharmacy in the US.