Cu ions released from copper-releasing Intra Uterine Devices (IUDs)
suppress sperm motility
Copper ions realeased from copper releasing IUDs decrease the sperm's ability to move and prevent the sperm from passing through the cervical mucus and going on to fertilize the egg.
An example of a copper releasing IUD is copper-T. It is made of a flexible, "T" shaped piece of plastic wrapped with a thin copper containing wire.