The intrauterine system (IUS) is one of the most effective birth control methods. The protection it gives is comparable to that of sterilization and begins immediately after insertion into the womb.

The contraceptive protection offered by the IUS is based on the local effects of the device and the progestin on the uterus.

	The plug of mucus in the cervix becomes thicker. This prevents the sperm from entering the uterus and also provides additional protection against pelvic infections.
	The cyclic build-up of the uterine lining is substantially reduced, there is a marked decrease in its thickness. This makes it impossible for an egg to become embedded in the lining of the uterus.

The intrauterine system does not provide protection against HIV or other sexually transmitted diseases.

If you want to have sex with a partner you know little about you should also use a condom.