A woman can get pregnant if a man’s sperm reaches one of her eggs (ova). Contraception tries to stop this happening by keeping the egg and sperm apart or by stopping egg production. One method of contraception is the IUS, or intrauterine system (sometimes called the hormonal coil).
An IUS is a small, T-shaped plastic device that is inserted into your womb (uterus) by a specially trained doctor or nurse.
The IUS releases a progestogen hormone into the womb. This thickens the mucus from your cervix, making it difficult for sperm to move through and reach an egg. It also thins the womb lining so that it's less likely to accept a fertilised egg. It may also stop ovulation (the release of an egg) in some women.
The IUS is a long-acting reversible contraceptive (LARC) method. It works for five years, so you don't have to think about contraception every day or each time you have sex. The brand name of the IUS used in the UK is Mirena.
You can use an IUS whether or not you've had children.
At a glance: facts about the IUS
- It's more than 99% effective. Less than one in every 100 women who use the IUS will get pregnant in five years.
- It can be taken out at any time by a specially trained doctor or nurse and your fertility quickly returns to normal.
- The IUS can make your periods lighter, shorter or stop altogether, so it may help women who have heavy periods or painful periods.
- It can be used by women who can't use combined contraception (such as the combined pill), for example those who have migraines.
- Once the IUS is in place, you don't have to think about contraception every day or each time you have sex.
- Some women may experience mood swings, skin problems or breast tenderness.
- There's a small risk of getting an infection after it's inserted.
- It can be uncomfortable when the IUS is put in. Painkillers can help with this.
- The IUS can be fitted at any time during your monthly menstrual cycle, as long as you're definitely not pregnant. Ideally, it should be fitted within seven days of the start of your period because this will protect against pregnancy straight away. You should use condoms for seven days if the IUS is fitted at any other time.
- The IUS does not protect against sexually transmitted infections (STIs). By using condoms as well as the IUS, you'll help to protect yourself against STIs.
How the IUS works
How it prevents pregnancy
Having an IUS fitted
How to tell whether an IUS is still in place
Removing an IUS
How it prevents pregnancy
The IUS is similar to the IUD (intrauterine device), but works in a slightly different way. Rather than releasing copper like the IUD, the IUS releases the hormone progestogen, which is similar to the natural hormone progesterone that's produced in a woman's ovaries.
Progestogen thickens the mucus from the cervix (opening of the womb), making it harder for sperm to move through it and reach an egg. It also causes the womb lining to become thinner and less likely to accept a fertilised egg. In some women, the IUS also stops the ovaries from releasing an egg (ovulation), but most women will continue to ovulate.
If you're 45 or older when you have the IUS fitted, it can be left until you reach menopause or you no longer need contraception.
Having an IUS fitted
- most GP surgeries
- community contraception clinics
- some GUM clinics
- sexual health clinics
- some young people's services
Find a clinic near you
An IUS can be fitted at any stage of your menstrual cycle, as long as you are not pregnant. If it's fitted in the first seven days of your cycle, you will be protected against pregnancy straight away. If it's fitted at any other time, you need to use another method of contraception (such as condoms) for seven days after it's fitted.
Before you have an IUS fitted you will have an internal examination to determine the size and position of your womb. This is to make sure that the IUS can be positioned in the correct place.
You may also be tested for any existing infections, such as sexually transmitted infections (STIs). It is best to do this before an IUS is fitted so that any infections can be treated. Sometimes, you may be given antibiotics at the same time as an IUS is fitted.
It takes about 15 to 20 minutes to insert an IUS:
- the vagina is held open, like it is during a cervical screening (smear) test, and
- the IUS is inserted through the cervix and into the womb
The fitting process can be uncomfortable or painful for some women, and you may also experience cramps afterwards.
You can ask for a local anaesthetic or painkillers before having the IUS fitted. Discuss this with your GP or nurse beforehand. An anaesthetic injection itself can be painful, so many women have the procedure without one.
Once an IUS is fitted it will need to be checked by a doctor after three to six weeks to make sure that everything is fine. Speak to your GP or clinician if you have any problems after this initial check or if you want the IUS removed.
Also speak to your GP if you or your partner are at risk of contracting an STI as this can lead to infection in the pelvis.
See your GP or go back to the clinic if you:
- have pain in your lower abdomen
- have a high temperature
- have a smelly discharge
This may mean you have an infection.
How to tell if an IUS is still in place
An IUS has two thin threads that hang down a little way from your womb into the top of your vagina. The GP or clinician that fits your IUS will teach you how to feel for these threads and check that the IUS is still in place.
Check your IUS is in place a few times in the first month and then after each period at regular intervals.
It is very unlikely that your IUS will come out, but if you can't feel the threads or if you think the IUS has moved, you may not be fully protected against pregnancy. See your doctor or nurse straight away and use extra contraception, such as condoms, until your IUS has been checked. If you've had sex recently, you may need to use emergency contraception.
Your partner shouldn't be able to feel your IUS during sex. If he can feel the threads, get your GP or clinician to check that your IUS is in place. They may be able to cut the threads a little. If you feel any pain during sex, go for a check-up with your GP or clinician.
Removing an IUS
Your IUS can be removed at any time by a trained doctor or nurse.
If you're not going to have another IUS put in and you don't want to become pregnant, use another contraceptive method (such as condoms) for seven days before you have the IUS removed. Sperm can live for seven days in the body and could fertilise an egg once the IUS is removed. As soon as an IUS is taken out, your normal fertility should return.
Who can use an IUS
Most women can use an IUS, including women who have never been pregnant and those who are HIV positive. Your GP or clinician will ask about your medical history to check if an IUS is the most suitable form of contraception for you.
Your family and medical history will determine whether or not you can use an IUS. For example, this method of contraception may not be suitable for you if you have:
An IUS may not be suitable for women who have untreated STIs. A doctor will usually give you a check-up to make sure you don't have any existing infections.
Using an IUS after giving birth
An IUS can usually be fitted four to six weeks after giving birth (vaginal or caesarean). You'll need to use alternative contraception from three weeks (21 days) after the birth until the IUS is put in. In some cases, an IUS can be fitted within 48 hours of giving birth. It is safe to use an IUS when you're breastfeeding, and it won't affect your milk supply.
Using an IUS after a miscarriage or abortion
An IUS can be fitted by an experienced doctor or nurse straight after an abortion or miscarriage, as long as you were pregnant for less than 24 weeks. If you were pregnant for more than 24 weeks, you may have to wait a few weeks before an IUS can be fitted.
Advantages and disadvantages of the IUS
Although an IUS is an effective method of contraception, there are several things to consider before having an IUS fitted.
Advantages of the IUS
- it works for five years
- it's one of the most effective forms of contraception available in the UK
- it doesn't interrupt sex
- an IUS may be useful if you have heavy or painful periods because your periods usually become much lighter and shorter, and sometimes less painful – they may stop completely after the first year of use
- it can be used safely if you're breastfeeding
- it's not affected by other medicines
- it may be a good option if you can't take the hormone oestrogen, which is used in the combined contraceptive pill
- your fertility will return to normal when the IUS is removed
There's no evidence that an IUS will affect your weight or that having an IUS fitted will increase the risk of cervical cancer, cancer of the uterus or ovarian cancer. Some women experience changes in mood and libido, but these changes are very small.
Disadvantages of the IUS
- Some women won't be happy with the way that their periods may change. For example, periods may become lighter and more irregular or, in some cases, stop completely.
- Irregular bleeding and spotting are common in the first six months after having an IUS fitted. This is not harmful and usually decreases with time.
- Some women experience headaches, acne and breast tenderness after having the IUS fitted.
- An uncommon side effect of the IUS is the appearance of small fluid-filled cysts on the ovaries – these usually disappear without treatment.
- An IUS doesn't protect you against sexually transmitted infections (STIs) so you may also have to use condoms when having sex. If you get an STI while you have an IUS fitted, it could lead to pelvic infection if it's not treated.
- Most women who stop using an IUS do so because of vaginal bleeding and pain, although this is uncommon. Hormonal problems can also occur, but these are even less common.
Risks of the IUS
Complications caused by an IUS are rare and usually happen in the first six months after it has been fitted. These include:
Damage to the womb
In rare cases (fewer than one in 1,000 insertions) an IUS can perforate (make a hole in) the womb or neck of the womb (cervix) when it is put in. This can cause pain in the lower abdomen but doesn't usually cause any other symptoms. If the doctor or nurse fitting your IUS is experienced, the risk of perforation is extremely low.
If perforation occurs, you may need surgery to remove the IUS. Contact your GP straight away if you feel a lot of pain after having an IUS fitted. Perforations should be treated immediately.
Pelvic infections may occur in the first 20 days after the IUS has been inserted.
The risk of infection from an IUS is extremely small (fewer than one in 100 women who are at low risk of STIs will get an infection). A GP or clinician will usually recommend an internal examination before fitting an IUS to be sure that there are no existing infections.
Occasionally, the IUS is rejected (expelled) by the womb or it can move (this is called displacement). This is not common and is more likely to happen soon after it has been fitted. Your doctor or nurse will teach you how to check that your IUS is in place.
If the IUS fails and you become pregnant, your IUS should be removed as soon as possible if you are continuing with the pregnancy. There's a small increased risk of ectopic pregnancy if a woman becomes pregnant while using an IUS.
Where to get the IUS
Most types of contraception are available free in the UK. Contraception is free to all women and men through the NHS. Places where you can get contraception include:
- most GP surgeries – talk to your GP or practice nurse
- community contraception clinics
- some genitourinary medicine (GUM) clinics
- sexual health clinics – they also offer contraceptive and STI testing services
- some young people’s services (call 0800 567 123 for more information)
Find sexual health services near you, including contraception clinics.
Contraception services are free and confidential, including for people under the age of 16.
If you're under 16 and want contraception, the doctor, nurse or pharmacist won't tell your parents or carer as long as they believe you fully understand the information you're given and your decisions. Doctors and nurses work under strict guidelines when dealing with people under 16.
They'll encourage you to consider telling your parents, but they won't make you. The only time that a professional might want to tell someone else is if they believe you're at risk of harm, such as abuse. The risk would need to be serious, and they would usually discuss this with you first.