Medway Sexual Health logo

What is it?

An Intra-Uterine System (IUS) is small, T-shaped plastic device that is inserted into the uterus. The IUS that is available in the UK is called Mirena.

An IUS releases the hormone progestrogen and works by:

• Thickening cervical mucus to prevent sperm reaching an egg
• Thinning the lining of the uterus to stop eggs from implanting
• Stops a fertilised egg from implanting in the uterus

A nurse or doctor will fit the IUS. There is a brief internal examination, followed by the fitting which takes 15-20 minutes. Once an IUS is fitted, it will need to be checked by a doctor after three to six weeks.

How effective is it?

An IUS is more than 99 per cent effective at preventing pregnancy. This means that fewer than one in every 100 women who use the IUS will get pregnant in a year.

What are the advantages?

• Once the IUS is in place, you don't have to think about contraception for five years
• An IUS is useful if you forget to take a pill at the same time every day
• Once an IUS is removed your fertility quickly returns to normal
• It does not interrupt sex
• It is not affected by other medicines
• It is safe to breastfeed after an IUS is fitted
• It can make your periods lighter, shorter or stop altogether, so it may help women who have heavy or painful periods

What else do I need to know?

• It does not protect you against STIs so always use a condom
• May not be suitable for some women - a full medical history should be taken. Some women experience irregular light bleeding during the first three months

Where can I get an IUS?

The IUS is available from all contraceptive and sexual health clinics and your GP. Find your nearest services using our Find a Service page.

For more information about contraception visit www.nhs.uk/worthtalkingabout ›