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Intrauterine System

What is it and how does it work?

The intrauterine system (IUS) is a small, plastic T-shaped device containing the hormone progestogen. It's inserted into the womb by a doctor or nurse. Two soft threads are attached to the end and hang down a little way into the vagina so you can check it's in place. It works for five years.

The IUS is more than 99 per cent effective. This means that using this method, on average fewer than one woman in 100 will get pregnant in a year.

An IUS is usually fitted during the first seven days of your period, when it provides immediate contraceptive protection. If fitted on any other day, an extra method of contraception must be used for seven days.

The IUS works by:

  • stopping sperm reaching the egg by thickening the mucus from the cervix

  • stopping the egg settling in the womb

  • sometimes stopping the ovaries releasing an egg each month (ovulation)


  • It's very effective.

  • It doesn't interfere with sex.

  • It works for five years.

  • Periods become shorter, lighter and less painful after three months.

  • Fertility returns quickly once it's removed.

  • You don't have to think about contraception for as long as it works.

  • If you change your mind, it's easily removed.


  • Most women have irregular, light bleeding to start with, but this should settle down after three months.

  • Temporary side effects can include headaches, acne and breast tenderness, which should clear up after a few months.

  • Some women may develop cysts on their ovaries. These aren't dangerous, often have no symptoms and usually disappear without treatment.

  • The IUS can be pushed out of the womb (expulsion) move or perforate (go through) the lining of the womb or cervix. This is rare when fitted by an experienced doctor or nurse. Check the threads every month to make sure it's still in place.

Can anyone use an IUS?

The IUS doesn't suit everyone. Reasons not to use it include thinking you might be pregnant and if you have now or have had in the past:

  • cancer of the womb or ovary

  • active liver disease

  • unexplained bleeding from the vagina

  • an untreated sexually transmitted infection or pelvic infection

  • problems with your womb or cervix

General comments

You'll need a check-up four to six weeks after the IUS is inserted. Do contact your doctor or nurse if you have any problems. You will be taught to feel the threads regularly too.

Where to get it

The IUS can be fitted by a trained GP or Gynaecologist

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