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The intrauterine system (IUS)

An IUS is a small T-shaped plastic device which contains a progestogen hormone. This is similar to the natural progesterone that women produce in their ovaries.

A trained doctor or nurse will put the IUS into your womb. It slowly releases the progestogen hormone. The IUS has two soft threads at one end which hang through the opening at the entrance of your womb (cervix) into the top of your vagina. An IUS works for up to five years. The IUS available in the UK is called Mirena.

How effective is an IUS?

How effective any contraceptive is depends on how old you are, how often you have sex and whether you follow the instructions.

If 100 sexually active women don’t use any contraception, 80 to 90 will become pregnant in a year. The IUS is over 99% effective. This means of every 100 women who use an IUS, less than 1 woman will get pregnant in a year.

When will an IUS start to work?

Immediately, if it is fitted within the first seven days of your menstrual cycle. If it is fitted at any other time, you will need to use an extra contraceptive method for the first seven days.

How does an IUS work?

  • It makes the lining of your womb thinner so it is less likely to accept a fertilised egg
  • It also thickens the mucus from your cervix. This makes it difficult for sperm to move through it and reach an egg
  • In some women it stops the ovaries releasing an egg (ovulation), but most women who use an IUS ovulate

What are the advantages of an IUS?

  • It works for five years
  • You don't have to think about contraception for as long as it works
  • It doesn't interrupt sex
  • Your periods usually become much lighter and shorter, and sometimes less painful, so an IUS can be useful if you have heavy, painful periods
  • Your normal fertility returns quickly when the IUS is removed
  • Unlike some methods of contraception, the IUS is not affected by other medicines. t

What are the disadvantages of an IUS?

  • Most women have irregular bleeding for the first three months or so. This should settle down
  • You may get temporary side-effects such as headaches, spotty skin and breast tenderness. These usually go away after a few months
  • Some women may have cysts on their ovaries in the first few months. These are not dangerous and do not usually need to be treated. Often there are no symptoms, but some women may have pelvic pain. These cysts usually disappear without treatment
  • There is a very small chance of you getting an infection during the first 20 days after an IUS is put in. You may be advised to have a check for any possible existing infection before an IUS is fitted
  • An IUS does not protect you against sexually transmitted infections, so you may need to use condoms as well
  • The IUS can be pushed out by your womb (expulsion) or it can move (displacement). This is more likely to happen soon after it has been put in and you may not know it has happened. This is why your doctor or nurse will teach you how to check your IUS threads every month
  • It is not common, but there is a risk that an IUS might go through (perforate) your womb or cervix when it is put in. This may cause pain, but often there are no symptoms. If this happens, the IUS may have to be removed by surgery. The risk of perforation is low when an IUS is fitted by an experienced doctor or nurse.

Can anyone use an IUS?

Most women who want to use an IUS can do so, including women who have never been pregnant and women who are HIV positive. Your doctor or nurse will need to ask you about your own and your family's medical history. Do mention any illness or operations you have had. Some of the conditions which may mean you should not use an IUS are:

  • you think you might already be pregnant

You have now or have had in the past:

  • cancer of the womb or ovary, or breast
  • active liver disease
  • unexplained bleeding cancer of the womb or ovary, or breast active liver disease unexplained bleeding from your vagina (for example, between periods or after sex)
  • a heart attack, stroke (severe arterial disease) or thrombosis (blood clots)
  • an untreated sexually transmitted infection or pelvic infection
  • problems with your womb or cervix.

Where can I get an IUS?

You can go to a family planning clinic, sexual health clinic or to your general practice. Some GPs and practice nurses will fit an IUS, but not all. All treatment is confidential and free.

How is an IUS put in?

An IUS is best fitted during the first seven days of your menstrual cycle, but it can be fitted at any time. The doctor or nurse must make sure there is no chance of you being pregnant. They will examine you internally to find the position and size of your womb before they put in an IUS. Sometimes they will check for any possible existing infection. It is best to do this before the IUS is put in. Sometimes antibiotics may be given to you at the same time as fitting the IUS.

Fitting an IUS takes about 15-20 minutes. It can be uncomfortable, or painful for some women, and you might want to have a painkiller or local anaesthetic. Your doctor or nurse should talk to you about this beforehand. You may get a period-type pain after the IUS is fitted. Painkillers can help with this.

What if I feel unwell after the IUS is fitted?

If you feel unwell and have any pain in your lower abdomen, with a high temperature or a smelly discharge from your vagina in the first three weeks after the IUS is fitted, see a doctor or go back to the clinic where it was fitted as soon as possible. You may have an infection.

How will I know that the IUS is still in place?

An IUS has two threads attached to the end that hang a little way down from your womb into the top of your vagina. The doctor or nurse will teach you to feel for the threads to make sure the IUS is still in place. You should do this a few times in the first month and then after each period or at regular intervals.

It is very unlikely that an IUS will come out, but if you cannot feel the threads or if you think you can feel the IUS itself, you may not be protected against pregnancy. Use an extra contraceptive method, such as condoms, and see your doctor or nurse straight away. If you had sex recently, you might need to use emergency contraception .

Rarely, your partner may say he can feel the threads during sex. If this is the case, get your doctor or nurse to check the threads.

Is it safe to use tampons if I have an IUS fitted?

Yes, you can use either tampons or towels during your periods.

How often do I need to see a doctor or nurse?

You need to have your IUS checked by a doctor or nurse three to six weeks after it is put in. The IUS can stay in for five years. If you have any problems you can go and see your doctor or nurse at any time.

When can the IUS be removed?

A trained doctor or nurse can take out the IUS at any time, by pulling gently on the threads. If you are not going to have another IUS put in, and you don’t want to become pregnant, use an extra contraceptive method, such as condoms, for seven days before the IUS is taken out. This is to stop sperm getting into your body. Sperm can live for up to seven days inside your body, and could fertilise an egg once the IUS is removed. Your usual fertility returns quickly after the IUS is taken out. You will usually have a period within a month or so.

If you want to try for a baby start pre-pregnancy care such as taking folic acid and stopping smoking. You can ask your doctor or nurse for advice.

Will an IUS affect my periods?

Yes. At first there is usually irregular or longer bleeding. Most women find that after about three months, their periods become lighter than usual. They may continue to be irregular and many women find that their periods stop altogether. If this happens to you, do not worry as it is perfectly healthy. When the IUS is taken out your periods will return to how they were before it was put in.

What if I become pregnant while I am using an IUS?

Very few women become pregnant while using an IUS. If you do become pregnant, your doctor or nurse will need to discuss the situation with you and take out the IUS.

If you do become pregnant there is a small increased risk of you having an ectopic pregnancy. An ectopic pregnancy develops outside your womb, usually in a fallopian tube. If you think you might be pregnant or have a sudden or unusual pain in your lower abdomen, seek medical advice as soon as possible. This might be the warning sign of an ectopic pregnancy.

I've just had a baby. Can I use an IUS?

An IUS is usually put in from four weeks after a vaginal or caesarean birth. You will need to use another method of contraception from three weeks after the birth until the IUS is put in and for seven days afterwards. An IUS can be used while you are breastfeeding.

Can I use an IUS after an abortion or miscarriage?

An IUS can be put in immediately after an abortion or miscarriage if you were pregnant for less than 24 weeks. If you had a medical abortion (using pills) an IUS should be fitted in the first two days after the abortion is complete otherwise you will need to wait for four weeks. If it is not fitted immediately, you will need to use another method of contraception until the IUS is put in and for seven days afterwards.

How do I find out about contraception services?

Contraception is free for women and men of all ages through the National Health Service.

  • You can find out about all clinics from sexual health direct, run by fpa on 0845 310 1334 or visit the website
  • You can get lists of GPs from libraries, primary care trusts or health boards and some advice centres and helplines.
  • You can get details of your nearest family planning or sexual health clinic from: local directories, health centre, hospital, midwife or health visitor, advice centre, NHS Direct on 0845 46 47 (NHS 24 in Scotland 0845 4 24 24 24), primary care trust or health board.
  • Young people can also phone Brook on 0800 0185 023 or Sexwise on 0800 28 29 30 for details of the nearest young people’s clinic.

Emergency contraception

If you have had sex without using contraception or think your method might have failed there are two emergency methods you can use.

  • Emergency hormonal pills - must be taken up to three days (72 hours) after sex. They are more effective, the earlier they are taken after sex.
  • An IUD - must be fitted up to five days after sex, or up to five days after the earliest time you could have released an egg (ovulation).

Ask your doctor or nurse about getting emergency pills in advance, just in case you need them.

Sexually transmitted infections

Most methods of contraception do not protect you from sexually transmitted infections.

Male and female condoms, when used correctly and consistently, can help protect against sexually transmitted infections. Diaphragms and caps may also protect against some sexually transmitted infections. If you can, avoid using condoms containing Nonoxinol 9 (spermicidally lubricated), as this does not protect against HIV and may even increase the risk of infection.

How fpa can help you

Sexual health direct is a nationwide service run by fpa. It provides:

  • confidential information and advice on contraception, sexually transmitted infections, planning a pregnancy, pregnancy choices and sexual wellbeing
  • details of family planning clinics, sexual health clinics and other sexual health services
  • a wide range of leaflets on individual methods of contraception, common sexually transmitted infections, abortion and planning a pregnancy.


Phone 0845 310 1334
9am to 6pm Monday to Friday

Northern Ireland
Phone 028 90 325 488
Derry 028 71 260 016
9am to 5pm Monday to Thursday, 9am to 4.30pm Friday

Phone 0141 576 5088
9am to 5pm Monday to Thursday, 9am to 4.30pm Friday

or visit fpa's website

A final word

This leaflet can only give you basic information about the IUS. The information is based on the evidence and medical opinion available at the time this information was published. Different people may give you different advice on certain points. All methods of contraception come with a Patient Information Leaflet which provides detailed information about the method.

Remember - contact your doctor, practice nurse or a family planning clinic if you are worried or unsure about anything.

Registered charity number 250187 - Supported by the Department of Health. - © fpa

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