IUS (Intrauterine system)

An IUS is a small plastic device that’s put into your uterus (womb) and releases a progestogen hormone. This is similar to the natural progesterone produced by the ovaries.

The IUS works as contraception for three or five years depending on the type.

There are different types and sizes with different amounts of the progestogen hormone.

If you’re aged over 45 when a particular type of IUS (Mirena) is fitted, it’ll work as contraception until after the menopause when contraception isn’t needed.


Effectiveness: Over 99% effective at preventing pregnancy – one of the most effective methods there is.

Fit and forget: Once you've got one, you don't need to remember to take or use contraception. The IUS can work for 3 or 5 years depending which type you get.

Periods: May be lighter, shorter or less painful. May stop or become irregular.

STI protection: No. Use external condoms or internal condoms to help protect yourself from STIs.

Hormones: Releases the hormone progestogen.

The IUS is a method of long-acting reversible contraception (LARC). LARC is very effective because it doesn’t depend on you remembering to take or use contraception.

The IUS is over 99% effective. Less than one IUS user in 100 will get pregnant in one year.

If 100 sexually active women don’t use any contraception, 80–90 will get pregnant in a year.

Most people with a uterus can use an IUS, including those who’ve never been pregnant, young people and people who are HIV positive.

Your doctor or nurse will ask you about your medical history to check if the IUS is suitable. Mention any illness or operations you’ve had as you may need specialist care when the IUS is fitted.

You may be advised not to use an IUS if you:

  • think you might already be pregnant
  • have had a baby in the last four weeks (although it can be inserted immediately after the baby is born)
  • have symptoms of an untreated sexually transmitted infection or pelvic infection
  • have breast cancer or have had it in the past
  • have problems with your uterus or cervix
  • have serious liver disease
  • have unexplained bleeding from your vagina (for example between periods or after sex)
  • have arterial disease or history of serious heart disease or stroke.

You may still be able to use an IUS, even if you have any of the above conditions. Your doctor or nurse will discuss this with you.

  • You don’t have to remember to use it.
  • Your periods usually become much lighter and shorter and sometimes less painful. They may stop completely after the first year of use. This can be useful if you have heavy, painful periods.
  • Two types of IUS (Mirena and Levosert) can be used specifically to treat heavy periods.
  • It works for three, four or five years depending on type.
  • It can be used if you’re breastfeeding. 
  • Your fertility returns to normal as soon as the IUS is taken out.
  • It’s useful if you can’t use estrogens, like those in the combined pill, the contraceptive patch and the contraceptive vaginal ring.
  • It’s not affected by other medicines.

Mirena can be used to protect the lining of your uterus (womb) if you’re having hormonal replacement therapy (HRT).

  • Your periods may change in a way that isn’t acceptable to you
  • Some people may get side effects like acne, headaches or breast tenderness. These usually get better after the first few months.
  • Some people develop small fluid-filled cysts on their ovaries that may cause pain. These aren’t dangerous and usually don’t need treatment.
  • You’ll need an internal examination when the IUS is fitted.
  • The IUS doesn’t protect you from sexually transmitted infections so you may need to use condoms as well.
  • There’s a small chance of you getting an infection during the first few weeks after an IUS is put in. You may be advised to have a check for sexually transmitted infections before an IUS is fitted or at the time it’s fitted.
  • The IUS can be pushed out (expulsion) by your uterus (womb) or it can move (displacement). This isn’t common. It’s more likely to happen soon after the IUS has been put in and you may not know it’s happened. Your doctor or nurse will teach you how to check the threads every month so you know the IUS is in place.
  • It’s not common, but there’s a very small risk that the IUS might go through (perforate) your uterus or cervix when it’s put in. The risk is higher if you’ve recently given birth or are breastfeeding. This may cause pain, but often there are no symptoms and the uterus or cervix will heal by itself. The risk is low when an IUS is fitted by an experienced doctor or nurse. If it does happen, the IUS may have to be removed by surgery.
  • You’re unlikely to become pregnant while using an IUS but if you do, there’s a small risk of ectopic pregnancy. You’re less likely to have an ectopic pregnancy while you’re using an IUS than when you’re not using any contraception.
  • It releases the hormone progesterone. This thins the lining of your uterus thinner to stop a fertilised egg implanting.
  • It also thickens the mucus in your cervix. This stops sperm reaching an egg.
  • In some people, it stops the ovaries releasing an egg (ovulation), but most IUS users continue to ovulate.
  • An IUS does not cause an abortion.

Will an IUS affect my periods?

Yes. In the first six months, irregular bleeding or spotting is common.

Periods usually become lighter, shorter and less painful.

Many people find their periods stop altogether. This isn’t harmful.

Are tampons safe if I have an IUS?

Yes. It’s safe to use tampons or a menstrual cup.

Make sure that the menstrual cup is put in the correct place and not too high in the vagina.

Take care not to pull on the IUS threads when you’re removing tampons or a menstrual cup.

What if I think I'm pregnant?

The IUS is very effective and it’s unlikely you’ll get pregnant.

If you do, there’s a small increased risk of ectopic pregnancy. An ectopic pregnancy develops outside the uterus, usually in a fallopian tube. If you think you might be pregnant and/or have a sudden or unusual pain in your lower abdomen, seek medical advice as soon as possible.

If you get pregnant and want to continue the pregnancy, talk to a doctor or nurse as soon as possible. If it’s early in the pregnancy it’s usually recommended to remove the IUS as soon as possible. The doctor or nurse will discuss this with you.

What if I want to stop using the IUS and try to get pregnant?

If you want to stop using the IUS, go back to the doctor or nurse and ask for it to be taken out. Your periods and fertility will return to normal when the IUS is removed. If you don’t want to get pregnant, use additional contraception, such as condoms, or avoid sex, for seven days before the IUS is taken out and use another method of contraception from the day it’s removed. If you want to try for a baby, start pre-pregnancy care such as taking folic acid and stopping smoking. Ask your doctor or nurse for advice and see Planning a Pregnancy.

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

You may be able to have an IUS fitted at the time of vaginal delivery or caesarean section.

If an IUS isn’t fitted in the first 48 hours after you give birth you’ll need to wait until four weeks after the birth.

You’ll need to use another method of contraception from three weeks (day 21) after the birth until the IUS is put in.

An IUS can be used safely while you’re breastfeeding and won’t affect your milk supply.

Can I use an IUS after a miscarriage or abortion?

An IUS can be put in by an experienced doctor or nurse immediately after a miscarriage or abortion. You’ll be protected from pregnancy straight away.

You can go to a contraception or sexual health clinic. Some doctors and nurses at general practices will be able fit an IUS.

When will an IUS start to work?

An IUS can be put in at any time in your menstrual cycle if it’s certain you’re not pregnant.

If it’s fitted in the first seven days of your menstrual cycle it’s effective immediately.

If it’s fitted at any other time, you’ll need to use additional contraception for the first seven days.

If you have a short menstrual cycle, with your period coming every 23 days or less, you may need additional contraception for the first seven days.

How's an IUS put in?

The IUS is inserted into your uterus (womb). A doctor or nurse will examine you internally to check the position and size of your uterus. Sometimes they’ll check for any existing infection. This can be done before or at the time of fitting the IUS.

Sometimes you’ll be given antibiotics at the same time the IUS is fitted.

Your appointment will last 20–30 minutes. Inserting the IUS usually takes around 5 minutes.

It can be uncomfortable or painful for some people, and you may be offered a local anaesthetic. Your doctor or nurse should talk to you about this.

You may get a period-type pain and some light bleeding after the IUS is fitted. Pain-relieving medicine can help with this.

What if I feel unwell after the IUS is put in?

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

How will I know that the IUS is in place?

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

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

Rarely, a partner may say they can feel the threads during sex. If this happens, ask your doctor or nurse to check the threads.

How's an IUS taken out?

A trained doctor or nurse can take the IUS out by pulling gently on the threads. If you want to keep using an IUS, the doctor or nurse can put in a new one at the same time.

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

You may be given an appointment 3-6 weeks after your IUS is put in, but this isn’t always necessary.

Contact your doctor or nurse if you have any problems, questions or want the IUS removed.

If a particular type (Mirena) is fitted when you’re 45 or over, it works as contraception until after the menopause when contraception isn’t needed.

It’s important to seek advice if you think you could be at risk of getting a sexually transmitted infection as this can lead to a pelvic infection.

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This website can only give you general information about contraception. The information is based on evidence-guided research from the World Health Organization and The Faculty of Sexual and Reproductive Healthcare of the Royal College of Obstetricians and Gynaecologists. 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 contraception clinic if you're worried or unsure about anything.