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There are two different types of IUDs, the copper IUD and the hormonal IUD. The IUD is an effective contraceptive that is inserted into the uterine cavity and is guaranteed to be effective for five years.

The copper coil protects against pregnancy by making it difficult for a fertilized egg that enters the uterine cavity to attach. In addition, the copper ions reduce the ability of sperm cells to fertilize the egg. Some people experience heavier bleeding than usual when using a copper coil.

The hormonal IUD protects against pregnancy by making it difficult for the fertilized egg that enters the uterine cavity to attach. In addition to acting as a foreign body like the copper IUD, it makes the uterine lining thin and impervious to the fertilized egg, while making the cervical mucus difficult for sperm to penetrate. Women who use the hormonal IUD will often experience lighter periods than normal. Many will experience that their periods stop. This is because the uterine lining is shrunk so much by the IUD hormone that nothing is going to come out of the uterus. Recently, two new hormonal IUDs have been introduced that are specifically designed for women who have not been pregnant or given birth. One lasts three years, the other lasts five years.