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The IUD and IUS Contraceptive Guide

The IUD and IUS are two methods of contraception that are a source of confusion for many. Not only do they have similar names and shapes, but they also act similarly as contraceptives and are 99% effective. IUD stands for 'intrauterine device' whilst IUS stands for 'intrauterine system'. The key to separating the two, however, is how they work to prevent pregnancy. To find out what how they work, keep reading.

Medically reviewed by Dr. Anand Abbot MRCGP Written by our editorial team Last reviewed 14-01-2024

What is an IUS? What is an IUD?

Both the IUD and IUS are small plastic, t-shaped devices that are measured and inserted into the uterus (womb) to prevent pregnancy. Unlike other methods of contraception such as the combined pill or the patches, they are long-acting reversible contraceptives (LARC). This means they can be left in for up to 5 to 10 years before they have to be replaced but can be removed at any point before then, if you want to change methods or get pregnant.

The key difference between them, however, is how they prevent pregnancy:


IUS releases the hormone progestogen to prevent pregnancy.


IUD releases copper to prevent pregnancy.

What is a intrauterine device (IUD)?

The IUD may also be referred to as 'the coil' and tends to be the more popular out of the two devices. It specifically works by releasing copper into the womb, which alters your cervical mucus. This makes it more difficult for sperm to reach an egg and survive as well as stopping a fertilised egg from being able to implant itself. It lasts for 5-10 years without needing to be replaced, but can be removed at any time you wish.

What is a intrauterine system (IUS)?

The IUS is similar to the IUD, except it is a hormonal contraceptive. It releases the hormone progestogen into the uterus, which similarly to the IUD, thickens the cervical mucus. This makes it more difficult for the sperm to move through the cervix and things the lining of the womb that a fertilised egg cannot implant itself. It also stops ovulation for some (the release of an egg each month). It needs to be replaced a bit sooner than the IUD, after around 3-5 years.

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Advantages and disadvantages of the IUD/IUS

The main advantages of the IUD and IUS is the effectiveness rate for preventing pregnancy. However, like other forms of contraception, there are additional benefits as well.


  • They are low maintenace as they can be left in for a long time and you don't have to rely on taking medication every day.
  • They can be used whilst breastfeeding, as they don't influence the mother's milk.
  • They can be removed any time you wish, and your fertility will go back to normal.
  • If you fall ill and have diarrhoea or vomit, the effectiveness is not altered like it is when you take 'the pill'.
  • They are good options if you're sensitive to oestrogen.
  • For some, they can reduce uncomfortable and severe period symptoms


  • They don't protect against STIS, you would need to use barrier contraceptives (e.g condoms).
  • Can cause spotting and bleeding for some. It should normally stop after a few months, but the device should be removed if it continues.
  • For some women, they can make periods heavier, longer and more painful. These symptoms may improve over a few months, but may not be the case for every woman.
  • May stop your periods which may not be suitable for women who use them to know whether their contraception has worked.
  • Can cause side effects such as headaches, acne and breast tenderness, which go away for most women over time.
  • The IUS in particular can cause ovarian cysts (which do not cause any symptoms).

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How do I get an IUD/IUS fitted?

To get an IUD or IUS fitted, you must first book a doctor's appointment. Not every doctor's surgery will have this service, or only particularly nurses can fit the device, so ensure you tell the receptionist when booking the appointment.

You will be asked a number of questions before the fitting to confirm this is the right form of contraception for you. This includes being tested and treated for STIs if required. You will also need to decide the timespan.

Do remember that you can have the device removed earlier than expected for whatever reason, even if you opted for a 5-10 year contraceptive protection.

  • IUD and IUS can be fitted at any point in your menstrual cycle.
  • You will be protected straight away with the IUD. For the IUS, if fitted during the first 7 days of your cycle, you will be immediately protected. Any other time of the month, you will need to use condoms for the following 7 days.
  • A fitting includes a physical examination to determine size and placement of the device.
  • The procedure takes approximately 20 minutes to complete. It is similar to a smear test.
  • This can be uncomfortable and sometimes painful for some women. You can ask for pain relief if you wish.

After the procedure

It's perfectly natural to experience cramping or bleeding (spotting) after the procedure. You can take over-the-counter painkillers to help with the cramping. However, some women may feel minimal discomfort. If you feel any pain or discomfort, you should let your doctor know.

If you experience any severe abdominal pain, a high temperature and abnormal discharge, you should contact the GUM clinic or your GP as soon as possible. This may be a sign of an infeciton.

Is it still in place?

Both the IUD and IUS have threads that hang down similar to a tampon, but these remain inside the vagina. These won't be noticeable and your GP will tell you how to locate them during your fitting.

The probability of your device falling out is very unlikely but it's good to know the protocol if it happens to you. This is also called IUD/IUS expulsion.

IUD/IUS expulsion is not as noticeable as you would think. In fact, for many women there are no symptoms of the device coming out of the uterus whatsoever. This is why it's important to check your device periodically. If the IUD/IUS has moved, you're at risk of falling pregnant. If you know what to look out for, you're in the best scenario to remain protected.

  • Check a handful of times after its first fitted to get used to the device, then maybe once or twice a month from then on.
  • Wash your hands thoroughly before checking.
  • Then sit or squat in a comfortable position, put your index or middle finger into your vagina.
  • Locate your cervix - it's easier than you think! The cervix feels firm, it has been described as the tip of your nose.
  • From here, you should be able to feel the strings. This should just be the end.
  • If you feel something hard, that's the end of the device.
  • If you feel the strings feel any longer or shorter than before, this could mean the device has moved.
  • Do not try and move the device yourself or pull on the strings, book an appointment with your doctor or head to a sexual health clinic to get it checked out.

During pelvic examination and smear tests, you can also ask your doctor to check your IUD/IUS. They can move the strings to an easier place when they finish.

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Precautions/interactions of the IUD/IUS

Any complications associated with the IUD and IUS are rare, however, they can happen and this tends to be within the first few months of having the device inserted.

These devices are well-tolerated for most and can be used if you're HIV positive. Before having a fitting, you will need to be clear of any STIs. You shouldn't have an IUD/IUS if you:

  • have a pelvic infection
  • have an issue with your cervix or womb
  • have any unexplained bleeding

You need to tell your doctor if you:

  • have had an ectopic pregnancy
  • recently had an abortion
  • have an artificial heart valve

Risks of the IUD/IUS

The NHS states that there are "fewer than one in 1,000 cases" where the device will damage the womb. If you have pain in the lower abdomen, this could be the cause.

"Fewer than one in 100" will experience a pelvic infections. Other risks include rejection that was mentioned above and ectopic pregnancy if your IUD/IUS fails and you don't realise you've fallen pregnant.


Where can I get an IUD/IUS fitted

The IUD and IUS should ALWAYS be fitted by a medical professional. Once inserted, it should ONLY be removed by a medical professional.

The IUD/IUS can be fitted at certain doctor's surgeries, but do check before you make an appointment to avoid wasting your time. There is usually a special nurse or doctor that does the fittings.

GUM clinics (genitourinary clinics) and STI clinics can insert the IUD as well, especially as a form of emergency contraception if needed. Again, ask over the phone or in reception regarding the fitting.

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