Measures to prevent pregnancy after unprotected sexual intercourse involve two primary methods: hormonal and physical. In the hormonal method, oral contraceptives commonly known as the “morning after” pill should be taken in a high dose as soon as possible after the event, preferably within 12 hours but no later than 72 hours. These pills contain a significant dosage of the hormone progesterone. In the physical method, a doctor can insert an intrauterine device (IUD) within five days of unprotected sex. Both methods are believed to work by impeding the implantation of a fertilized egg in the uterus.