Contraception and the IUD (intrauterine device) and IUS (intrauterine system)
What are IUDs and IUSs?
IUDs and IUSs are both long-acting reversible contraceptive (LARC) methods.
An IUD, or intrauterine device, is a small, plastic and copper, flexible, T-shaped device that is placed into the uterus (womb) for contraception. There are various sizes and types of IUD available to suit the needs of different women. They can remain in the uterus for five to 10 years, depending on the type.
An IUS, or intrauterine system, is a small, T-shaped plastic device that contains progestogen. In the UK the brand name is Mirena, and the system can remain in the uterus for up to five years.
How do they work?
IUDs contain copper, which is slowly released into the uterine cavity. The copper stops the sperm from making it through the vagina and uterus to reach the egg, thus preventing fertilisation.
IUSs, such as Mirena, release the hormone progestogen, which causes the cervical mucous to become thicker so the sperm cannot reach the egg. The hormone also changes the lining of the uterus, so implantation of a fertilised egg cannot occur. This type of IUS must be replaced every five years.
How effective are the IUD and IUS?
IUDs and IUSs are over 99% effective.
How is an IUD or IUS used?
Once the IUD or IUS has been inserted by your doctor, you do not need to take any further steps to prevent pregnancy until it is time to replace it. How long it lasts depends on the type of IUD or IUS you receive.
Are there side effects associated with IUDs and IUSs?
IUDs and IUSs rarely cause serious side effects when used in a monogamous relationship (having only one sex partner). Side effects include pelvic inflammatory disease, painful and heavy periods, backaches, and headaches. Discuss these side effects with your doctor, nurse or family planning expert.
Mirena is associated with lighter menstrual periods.
Do IUDs protect against sexually transmitted infections?
No. IUDs do not protect against sexually transmitted infections (STIs), including HIV (the virus that causes AIDS). The male condom provides the best protection against STIs.