The Mirena coil: everything you need to know

Confused by coils? The Mirena is a popular part of an HRT regimen so here’s how to discover if it’s right for you

• The Mirena can be used as the progestogen part of HRT
• It can also be used as a contraception or to treat heavy, painful periods
• It’s effective for five years as a part of an HRT regimen so is a convenient option

First of all, let’s clarify what is the Mirena coil is exactly.

There are two main types of coil: the hormonal coil, which is known as an intrauterine system (IUS) and is a plastic T­-shaped device, and the intrauterine device (IUD), which is made of copper and plastic.

The Mirena is a type of hormonal coil (other types include Levosert, Benilexa, Kyleena and Jaydess). It’s very small and is inserted into your womb (uterus) where it gradually releases a hormone called levonorgestrel, a type of progestogen, into your womb.

There are two threads attached to the Mirena coil that pass out through the neck of your womb (cervix) and lie in your vagina. These allow you to check the coil is still there. They also mean it can be easily removed. They do not hang outside the body and your partner does not usually feel them during sexual intercourse.

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How does the Mirena coil work and what are the benefits?

As the progesterone part of HRT

HRT is the first line of treatment for women experiencing perimenopausal and menopausal symptoms. The Mirena coil replaces the progesterone your body produces less of during perimenopause and menopause with a progestogen (a synthetic version of progesterone). If you still have your womb, taking oestrogen can cause the womb lining (endometrium) to thicken. To prevent this, you will usually need to take progesterone, which thins the lining.

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Progesterone also ensures bleeding does not happen outside of the expected times, and has other health benefits, which you can read about here. While the Mirena is a synthetic progestogen, it is a much lower dose than the tablet versions of progestogen. It delivers the hormone directly to your uterus – this localised effect means potential side effects that can occur in some women who take progestogen tablets are minimised.

A treatment for heavy and painful periods

During perimenopause, it’s not unusual for women to experience heavy bleeding [1]. Although “normal”, heavy periods can cause disruption, distress and difficulties in every area of life, including work, exercise, social life and sex life.

The Mirena is recommended as a first‐line treatment for heavy bleeding by NICE [2] because the low dose of progestogen controls the development of the lining of the womb – it makes it thinner, which usually leads to periods becoming lighter and shorter or stopping. One study found that the levonorgestrel-releasing IUS (such as Mirena) can reduce blood loss by more than 90% over 6 months for most women with heavy menstrual bleeding [3].

RELATED: Heavy periods during the perimenopause: what you need to know

A very reliable contraceptive

The Mirena thickens the cervical mucus, making it difficult for sperm to get to the egg, and keeps the lining of the womb too thin to support a pregnancy. It’s therefore a highly effective form of contraception – it is over 99% effective [4]. It is safe, easy to use – once it is fitted, you don’t need to do anything – and it is useful for those who may struggle to remember to take a tablet. It is also a reversible method of contraception.

RELATED: Contraception during perimenopause: HRT, the pill and the Mirena coil

How long does the Mirena coil last?

The amount of time a Mirena coil can be left in place depends on its reason for use.

If you use the Mirena for contraception only, it is now licensed for eight years. If you use the Mirena purely for heavy menstrual bleeding, it is licensed for five years.

If you are using the Mirena as part of your HRT, for endometrial protection, it can be used for five years before you need to get it replaced. While the product license for Mirena is for four years for endometrial protection, the Faculty of Sexual & Reproductive Healthcare supports its use for five years.

What are the risks of the Mirena coil?

There are very few risks associated with insertion of the Mirena coil. These include:

• In a small number of women there can be difficulties with the insertion of the Mirena coil. This can be due to uterine malformation such as a bicornate uterus (heart-shaped uterus), large fibroids distorting the shape of the womb or a narrow entrance to the womb (cervical canal). On rare occasions it may not be possible to fit the device within a clinic, so alternative options will be discussed with you.
• Very rarely (in about 1-2 in every 1,000 cases), during insertion the Mirena coil can make a tiny hole in your womb called a perforation and an operation may be needed to remove the coil [5].
• Occasionally the Mirena coil may fall out of your womb (expulsion). This happens in approximately one in 20 women [6].

There are very few risks associated with use of the Mirena coil. These include:

• Pelvic infection, usually within 3 weeks of having an IUS fitted
• Ectopic pregnancy if the IUS fails
• A small increased breast cancer risk (14 extra cases of breast cancer per 10,000 women) in women aged 15 to 49, compared to those not using contraceptive medication [7]. By way of comparison, the contraceptive pill is thought to be linked to less than 1 in every 100 breast cancer cases in the UK [8].

Are there any side effects?

The Mirena coil can cause some irregular, light bleeding. It can lead to spotting or having a brown discharge that may continue for up to six months. After this time, it usually settles down and then there is usually no further bleeding.

Side effects are more common within the first few months of the Mirena coil being inserted; these may include breast tenderness, headaches, acne and symptoms similar to premenstrual syndrome (PMS), they usually settle after the first few months.

Are there any alternatives?

There are other types of hormonal coil (such as Kyleena and Jaydess) that can be used for contraception only, not as a part of HRT. They do not contain enough hormone to protect the womb lining.

There are hormonal coils which, like the Mirena, also contain 52 mg of levonorgestrel (Benelixa and Levosert). The FSRH supports the use of these coils for protection of the womb lining as part of a HRT regimen for five years as well as the Mirena.
There are also types of coils (IUD) that do not contain any hormones. Whilst these can work well for contraception, they cannot be used to protect the lining of your womb as part of HRT; they also do not lead to periods reducing or stopping.

Body identical progesterone capsules (such as Utrogestan) can be used as the progesterone part of HRT. 

How can I prepare for having a coil fitted?

You do not need any special preparation beforehand, although Clair Crockett, GP and menopause specialist at Newson Health recommends that you take your usual painkiller (for example paracetamol or ibuprofen) around one hour before your appointment time.

To ensure that there is no risk of pregnancy before the coil you are having inserted is fitted, ensure that you use adequate contraception or do not have sexual intercourse between your last period and having the coil fitted.

What will happen at my fitting?

‘You will usually be asked to sign a consent form,’ says Dr Clair. ‘This states that you agree to have the coil inserted and you understand what it involves. The clinician fitting the coil will spend time talking you through what is in the form and give you opportunity to answer questions.’

How is a coil fitted?

‘Much like when you have a cervical smear test, you will be asked to lie on an examination couch and a speculum will be used so as the clinician fitting your coil can see your cervix,’ explains Clair. ‘At this point, if you are having any form of local anaesthetic, this will be applied. A small measuring device is passed through your cervix and into your womb. This measures the length of your womb to ensure that the coil is fitted correctly. The coil is then passed into your womb within a small tube (an introducer), and the coil is released once it’s in the correct position. The introducer is removed, and the threads of the coil are then visible in the vagina. These are trimmed so they fit neatly, without you being able to feel them unless actively seeking to.’

Will I feel any pain?

Many women do not feel any pain when having a coil inserted. However, some women feel ‘period­like’ discomfort during, and after the fitting. Sometimes this can be quite severe around the time of the fitting, but is usually very short lived.

What do I need to do after I go home?

When you leave the clinic, you can return to your normal activity. You should not use tampons for the next four weeks. If you are using the Mirena coil for contraception, it will be effective seven days after insertion ­so additional contraception (such as condoms) will be needed if you have sexual intercourse in the first week. ‘This advice is the same for any hormonal coil,’ says Dr Clair. ‘A non-hormonal (copper coil) is effective immediately.’

You may experience some bleeding, which is normal. If you have period pains, you can take your usual painkillers, such as paracetamol or ibuprofen. ‘If pain is not relieved by painkillers, or you are continuing to experience pain more than a week after the coil was inserted, I would advise that you see your GP or contact the clinic where the coil was fitted for advice,’ says Dr Clair.

Will I have a follow­-up appointment?

Most women do not need a follow up appointment. ‘In the past it was common practice to be invited for a coil check after six weeks, however, this is no longer recommended routine practice as most women will be able to feel their coil threads when they insert a finger into their vagina,’ says Dr Clair. ‘If the coil threads are felt, and there is no ongoing pain, then this would suggest all is well. However, if you would like a review appointment to have a coil check then this can be arranged on request.’ This will involve passing a speculum to check the coil threads can be seen, which confirms the coil is in position.

RELATED: The Mirena coil: your FAQ

 References

1. Paramsothy P., Harlow S.D., Greendale G.A., Gold E.B., Crawford S.L., Elliott M.R., Lisabeth L.D., Randolph J.F. Jr. (2014), ‘Bleeding patterns during the menopausal transition in the multi-ethnic Study of Women’s Health Across the Nation (SWAN): a prospective cohort study’, BJOG. 121(12):1564-73. doi: 10.1111/1471-0528.12768
2. NICE (2018): heavy menstrual bleeding: assessment and management
3. Creinin MD, Barnhart KT, Gawron LM, Eisenberg D, Mabey RG Jr, Jensen JT. Heavy Menstrual Bleeding Treatment With a Levonorgestrel 52-mg Intrauterine Device. Obstet Gynecol. 2023 May 1;141(5):971-978. doi: 10.1097/AOG.0000000000005137
4. NHS: Methods of contraception: IUS hormonal coil
5. FSRH Clinical Guideline Intrauterine Contraception
6. NICE: CKS: Contraception – IUC: Risks, adverse effects, associated problems
7. Mørch LS, Meaidi A, Corn G, Hargreave M, Wessel Skovlund C. (2024), ‘Breast Cancer in Users of Levonorgestrel-Releasing Intrauterine Systems,’ JAMA, 332(18) pp1578–1580. doi:10.1001/jama.2024.18575
8. Breast Cancer Now