Reviewed September 2018

IUS vs IUD: which is best for me?

ius vs iud which one is best for me

When you decide to go on a form of contraception, it can be a minefield trying to decipher which one is best suited to you, and there may be a lot of thoughts and questions going through your mind — which is safest? What are the side effects? How will the extra hormones affect my body? Will it be uncomfortable? Will it suit my lifestyle?

Even once you have made part of the decision, such as deciding, for example, to get a coil rather than a pill, there are still choices to be made, namely whether you want one with hormones, or without. Here, we look at two different types of coil, the Mirena IUS and the copper coil, to help you work out which one is more suited to your situation.

The copper coil

The copper coil, otherwise known as an intrauterine contraceptive device or IUD, is a plastic carrier made of copper wire or copper bands. It works in a mechanical fashion by making it difficult for a fertilised egg to attach to the womb, and the copper also makes the womb a hostile environment to sperm swimming up to reach the egg. It can be kept in place for 5-10 years, and because of its ability to stop a fertilised egg implanting it can be used as emergency contraception if needed.

The Mirena IUS

The intrauterine contraceptive system, or IUS (brand name Mirena), is a plastic device coated with a synthetic form of progesterone hormone called levonorgestrel. This is inserted and the hormone released slowly and steadily over the course of either three or five years, depending on the system used. The IUS works by making cervical mucus thicker, and therefore more difficult for sperm to reach an egg. On top of that, it stops the lining of the womb from growing, so should an egg be fertilised it cannot implant, and in some women it can even prevent ovulation.

So far so good — but when it comes to specific things you may want from your coil, which type fares better, or is more suited to you?

Preventing pregnancy

With the Mirena IUS, the risk of pregnancy is very low, and it is said to be as effective as being sterilised.1 The risk of having an ectopic pregnancy is also lower than if you had no contraception at all. However, should a pregnancy occur with the IUS in place, the chances of it being ectopic is about 1 in 20,2 so it is therefore important to seek medical advice immediately should you get pregnant with this type of contraception in place.

The pregnancy rate with coils can be very low, fewer than 20 in 1000 over five years,3 and for some types it can be considered as a form of reversible sterilisation. However, the risk of pregnancy with an IUD is very slightly higher than the risk of pregnancy with the Mirena IUS.

How does each affect my periods?

As the Mirena is a hormonal contraceptive, it can affect periods, making them irregular, or even non-existent. This is because the synthetic progesterone in the Mirena affects the lining of the womb, stopping it from growing. Irregular periods tend to settle with time, usually around three months after insertion. Not having periods can actually come as quite a relief for some users, particularly if they experienced heavy, painful periods prior to insertion. For this reason, the Mirena is often used by people who have conditions such as fibroids or endometriosis, as it has been proven to reduce their symptoms.

As the Mirena is a hormonal contraceptive, it can affect periods, making them irregular, or even non-existent. This is because the synthetic progesterone in the Mirena affects the lining of the womb, stopping it from growing.

With the copper coil, however, periods can become heavier than they were previously, as the coil causes a (harmless) inflammatory reaction within the lining of the womb. So, if you have heavy and/or painful periods already, this may affect your decision when it comes to choosing between the Mirena coil and the copper coil.

What about other side effects?

When it comes to other side effects, each type of coil has its own pros and cons. With the copper coil, for example, mood and libido changes have been reported as a side effect, at similar rates to those reported with the IUS.4

However, the IUD is an acceptable form of contraception for women who have found they are particularly sensitive to hormones, perhaps experiencing bad side effects on the pill previously, for example. On top of that, the IUD may be recommended if you have been advised not to have hormonal contraception due to liver problems or arterial diseases. However, if you have heavy, painful periods, or fibroids, then the copper IUD may not be suitable.

Some evidence says the Mirena coil can cause side effects such as nausea, mood disturbances and acne. In one study, 14 removals were reported due to premenstrual symptoms, and 13 due to depression and mood swings after five years.5 The same study reported seven removals due to acne among IUS users after five years.6 In general, while acne may be a side effect, it tends not to be a cause for removal however. Some women have reported weight gain as a side effect, although there is no proven evidence to support this,7 and no causal link has been established.

Discomfort in the vagina or during intercourse can occur with both types of coil, and this is more likely if the strings that hang down into the vagina (for you to check that your coil is in place) are a bit long.

Some people will get side effects with the Mirena and others won’t, as the IUS interferes with the body’s hormonal rhythm, and can disrupt the pattern in different ways for different women. In general, however, systemic side-effects are rare (and rarer than those seen with the progesterone-only pill, for example), as the dose of levonorgestrel absorbed in the womb is small.

Discomfort in the vagina or during intercourse can occur with both types of coil, and this is more likely if the strings that hang down into the vagina (for you to check that your coil is in place) are a bit long. If this is the case, you can go back to your doctor or sexual health clinic and ask them to cut the strings a little bit shorter.

Will I have any symptoms immediately after insertion?

The copper coil can be inserted at any time following a negative pregnancy test, but the Mirena IUS should ideally be inserted in the first seven days of your menstrual cycle, six weeks postpartum, or at any time between day one and five after a first-trimester abortion. Both will need to be done at a doctors surgery or a sexual health clinic, and require a trained professional to insert them.

With both, dizziness during and after the procedure can happen, as they are inserted through the cervix (neck of the womb) and the nerve supply in that region is connected to the nerve system that controls our blood pressure.

With both devices, it is important to watch out for signs of pelvic inflammation and womb perforation in the days following insertion, signs which could include pain, change in discharge, problems passing urine or stools, and unusual bleeding.

With both devices, it is important to check they are in place on a regular basis (after the first period or between three to six weeks following insertion) by feeling for the strings in the vagina. Following this, regular checking schedule is usually discussed by the person inserting the coil.

Ultimately, unless one particular type of coil is unsuitable for you because of a medical condition, it is up to you to decide which will suit you best, and you may wish to take into account your tolerance for hormonal methods, and how heavy your periods are. If you get a coil fitted and find that actually you aren’t happy with it, you can always have it removed, although it is advised to keep it in for at least six months as side effects to tend to settle down with time.

Although many people are very happy with both the copper IUD and the Mirena IUS, up to 60% of women and 50% of women respectively stop using them within five years of insertion.8 The most common reasons for this are vaginal bleeding and pain with both. Nonetheless, just because one woman experiences a specific symptom, it doesn’t mean you will, and if you are looking for a long term form of contraception, either the IUS or the IUD could be perfect for you.

Last updated September 2018
Next update due 2020

Dr. Deyo Famuboni, MB ChB

Dr. Deyo Famuboni is a UK trained GP with over 10 years of medical experience. After graduating from the University of Edinburgh, she went on to do further training within a wide range of medical specialities including obstetrics and gynaecology. She has spent time working abroad as well as within the NHS and private sectors in the UK. She is a member and clinical advisor of the Royal College of General Practitioners and a diplomate of the Royal College of Obstetrics and Gynaecology, Royal College of Paediatricians and the Faculty of Sexual and Reproductive Health. She also has a strong interest in nutrition and health.

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  1. NICE, ‘Long-acting reversible contraception’, NICE Clinical Guideline CG30, [website], 2014,, (accessed 15 August 2018).
  2. Ibid.
  3. Ibid.
  4. Ibid.
  5. M. Cox et al., ‘Clinical performance of the levonorgestrel intrauterine system in routine use by the UK Family Planning and Reproductive Health Research Network: 5-year report’, J Fam Plann Reprod Health Care, Vol. 28, No. 2, 2002, pp. 73-7.
  6. Ibid.
  7. NICE, ‘Long-acting reversible contraception’, 2014,, (accessed 15 August 2018).
  8. Ibid.