Contraception: Intrauterine System (IUS)

An Intrauterine System (IUS) is small T-shaped piece of plastic which contains a reservoir of a progestogen (a hormone). The device is inserted into the uterus (womb) and can remain there for three to five years depending on which brand is inserted. An IUS is 99 per cent effective as a contraceptive device and once inserted needs no further maintenance beyond checking that it is still in place.

How does it work?

Currently, there are three brands of IUS available in the UK: Jaydess®, Levosert® and Mirena®. These systems release a synthetic hormone called levonorgestrel from the reservoir within the device. Levonorgestrel causes the lining of the womb (the endometrium) to become thinner preventing a fertilised egg from implanting. It also causes thickening of the cervical mucus, which helps to stop sperm getting through. In some women ovulation (release of an egg from the ovaries) is also suppressed.

What are the advantages of an IUS?

  • An IUS is a highly effective, reversible form of contraception - Jaydess® and Levosert® can be left in place for up to three years while Mirena® can be left in place for up to five years. These systems reduce menstrual blood loss and are therefore a good choice for women with heavy periods. They may also reduce period pain and make periods shorter.
  • An IUS can be removed at any time and fertility will return straight away.

What are the disadvantages of an IUS?

  • An IUS has to be fitted into position. This may be a little uncomfortable and painkillers or a local anaesthetic may be given prior to the insertion.
  • In the first three months after insertion, irregular, light bleeding may occur. After this periods will become regular again and will usually be lighter than before the IUS was fitted.
  • An IUS provides no protection against sexually transmitted infections (STIs), including HIV.
  • Some women may develop small, harmless cysts on the ovaries but these usually disappear without treatment.

Are any regular checks necessary?

An IUS has two threads attached to it which come through the cervix into the womb. The doctor or nurse will show you how to feel the threads - they should be checked regularly each month to ensure that the IUS is still in the correct position.

The IUS will be checked by a doctor or nurse four to six weeks after insertion and then once a year unless there is a problem.

Further information available from:

FPA (Sexual Health Charity)
23-28 Penn Street
London N1 5DL
Tel: 020 7608 5240

Fact sheet provided by MIMS

Date last reviewed: September 2016

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