Reversible methods of contraception include the use of a system or device placed inside the uterus. The IUD is a copper device inserted into the uterus to prevent pregnancy. The intrauterine system (IUS) contains hormones that will be gradually released and provide effective contraception until removed.
The review of trials compared IUDs to IUSs and found there was no difference in the rate of unplanned pregnancies. The review found that a lack of menstrual bleeding is more likely with IUS use and that IUD use is more likely to cause heavy menstrual bleeding and pain.