Mirena coil (IUS)

Written by Monica Karpinski, medically reviewed by Dr. Lotte Elton

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How the Mirena coil works | How effective is the Mirena coil? | Who is the Mirena coil suitable for? | What’s it like having the Mirena inserted? | What’s it like having the Mirena removed? | Benefits of the Mirena | Side effects of the Mirena | Other risks and complications

Read more:

Is the Mirena coil right for me? | How will I know if my Mirena coil has stopped working? | Can the Mirena coil help with heavy bleeding? | Pregnancy symptoms with the Mirena coil: should I worry?

If you are interested in long-lasting contraception that doesn’t require you to take a pill every day, the Mirena coil may well be worth considering. The Mirena is a type of intrauterine system (IUS) that is placed inside the womb. It is a small, T-shaped device, and the diameter of the tube used to insert it into the womb is just 4.40mm¹ — the size of the top of a pushpin.

The name “Mirena” is a brand name, given by its manufacturer Bayer Healthcare. Medically, the Mirena is classified as a “levonorgestrel intrauterine system” (LNG-IUS), which is a hormone-releasing device, and is one of four LNG-IUS available in the UK.

The Mirena coil is inserted into the womb through an insertion tube and protects against pregnancy for five years, but there is evidence to suggest that it may be effective for longer.² However, the Mirena is licenced for five years of use, which means that unless there is another reason for your coil to be taken out early, it should be replaced after five years.

During the Covid-19 pandemic, some women were advised by healthcare practitioners that they could extend their use of the Mirena coil because of the risk of Covid-19 transmission if they attended medical appointments. However, the Faculty of Sexual and Reproductive Healthcare in the UK has now revised this guidance and recommends that women should attend for removal or replacement of the Mirena after 5 years.³

While the Mirena is over 99% effective when inserted correctly,⁴ it may not be suitable for everyone. For example, if you currently have breast cancer, or have a history of serious heart disease.⁵ See below for more explanation on who can have a Mirena coil.

Once it is inserted into your womb, the Mirena releases a type of progestogen called levonorgestrel. Progestogens are steroid hormones which help to maintain pregnancy and play a role in regulating the menstrual cycle.

The released levonorgestrel works to thicken the mucus in the cervix, which makes it difficult for the sperm to pass into the womb to fertilise the egg.⁶ Levonorgestrel also causes endometrial atrophy, which keeps the lining of the womb thin, and suppresses the production of large, dilated blood vessels required for an egg to successfully implant.⁷

In most cases, the Mirena does not affect the hypothalamic-pituitary-ovarian axis – the hormonal network between the brain and the ovaries. This means that most people with wombs (75%) who use the Mirena will continue to ovulate (release an egg from the ovaries).⁸

The Mirena coil is highly effective and has been found to have a lower rate of pregnancy than the copper coil (IUD).⁹ It is over 99% effective — in a 2004 Cochrane Review of over 61,000 users, there was less than one pregnancy (0.06) per 100 cisgender women in one year of use.¹⁰

It is safe for most, but not all, people with wombs to use the Mirena coil. It can be inserted at any time during your monthly cycle.

Criteria for the whether or not the Mirena is safe for use with certain conditions is defined by the UK Medical Eligibility Criteria (UKMEC), a set of guidelines that support clinicians in the UK in providing evidence-based care when it comes to contraception. As per these criteria, some conditions are considered to represent too great a health risk to be recommended. These include:¹¹

• If you’ve just given birth and have sepsis (postpartum sepsis)
• If you’ve just had an abortion and have sepsis(post-abortion sepsis)
• Current breast cancer
• Current endometrial or cervical cancer
• Active or recurrent pelvic inflammatory disease (PID)
• Sexually-transmitted infections (STIs) — however, the Mirena can be inserted before STI tests have been received if you are asymptomatic
• Abnormal and undiagnosed vaginal bleeding
• Gestational trophoblastic disease (molar pregnancy)
• Pregnancy — you cannot have the Mirena inserted if you are pregnant¹²

In some instances where the risks of using the Mirena are considered to outweigh the benefits, you may still be able to have the coil inserted under particular circumstances, as per expert clinical judgement.¹³ If any of the below conditions or scenarios are relevant to you, it is essential that you see your doctor for assessment. These include:

• A history of breast cancer
• HIV with a CD4 cell count of <200 cells/mm³
• Certain complications from organ transplants, including graft failure and rejection
• Certain cardiovascular conditions, including stroke; a history of, or current, ischaemic heart disease; and long QT syndrome
• A womb abnormality
• Certain liver diseases, including severe cirrhosis

When can a Mirena coil be inserted?

A Mirena coil can be inserted at any point during the menstrual cycle. However, the timing of insertion affects how quickly the Mirena coil becomes effective for preventing pregnancy.¹⁴

The Mirena coil is effective immediately if it is inserted within 7 days of the start of your period. If you have the Mirena coil inserted at any other time in the menstrual cycle, you should use other methods to prevent pregnancy (e.g. condoms) for the first 7 days.

If you are using combined hormonal contraception and you have the Mirena coil inserted in week 2 or 3 of the cycle, or day 1 of the hormone-free interval, you do not need to use any additional precautions (e.g. condoms) to prevent pregnancy, as long as you have taken the combined contraception correctly in the 7 days before insertion. If you have a Mirena coil inserted after day 1 of the hormone-free interval, or in week 1 of the cycle, then you should continue the combined contraception (or use additional contraception, like condoms) for 7 days.

Your doctor should take your full medical history before recommending you for the Mirena coil, including a screening for STIs. However, if you have been screened for STIs but haven’t yet received the results and aren’t exhibiting any symptoms, you can still have the coil inserted.¹⁵ If required, you can be treated for the STI once you receive the results.

If you do have symptoms of an STI and/or pelvic inflammatory disease — such as pelvic pain or unusual vaginal discharge — it is recommended that you delay the insertion of the coil until your condition is confirmed and has been treated.

If you have heavy periods, your doctor may also do a blood test or ultrasound, especially if other treatments to manage your heavy bleeds haven’t been effective or if you are at risk of other gynaecological diseases, before a Mirena will be recommended.¹⁶

The appointment for having the coil inserted should take less than 30 minutes, with the actual insertion itself taking no longer than five minutes. Your doctor or nurse will first talk you through the procedure before examining inside the vagina to check the position and size of the womb. Your doctor will perform any necessary tests, including for infection, during your appointment and prior to insertion. For insertion, the vagina is held open in the same way as during a smear test — inserting a speculum into your vagina and then gently opening it.

Experiences of pain and discomfort vary between women. While some women report excruciating pain, others describe the insertion as “uncomfortable” or “unremarkable”

The IUS is then inserted into the womb using an insertion tube. The Mirena is T-shaped, and the horizontal arms are folded and placed inside the tube. Once the Mirena has been inserted, the tube will be removed. The Mirena has two thin threads that will hang down from the bottom of the device and into the top of your vagina, and your doctor or nurse will explain how to feel for these threads to make sure the device is correctly in place.

Some people report taking painkillers prior to the insertion, however, there is no evidence from current trials that support use of painkillers to reduce pain during insertion.¹⁷ Local anaesthetic is not routinely required for insertion but is available if there are difficulties in inserting or removing the IUS.¹⁸

There is wide variation in clinical practice regarding the use of local anaesthetic before IUS/IUD insertion. Around a quarter or UK health professionals regularly use local anaesthetic for insertion, with another quarter either never or rarely offering it.¹⁹

Still, experiences of pain and discomfort vary from person to person. While some report excruciating pain, others describe the insertion as “uncomfortable” or “unremarkable”. Insertion is quick and whatever pain you experience should not last long.

There are many reasons why you might want to have your Mirena coil removed. For one, you may have decided that you would like to get pregnant, or you may find the side effects too troubling. You may have also had the Mirena in for five years, which means that it’s time for you to replace it.

Many people with wombs report that the removal procedure is much easier and simpler than insertion. After inserting a speculum, your doctor or nurse will grasp the threads of the device with forceps and gently give them a pull. The IUS should come out easily.

If the threads of your IUS are not visible (usually because they have curled up inside the cervix), then the doctor or nurse may use a device called a thread retriever. If this does not work, you may be referred to have an ultrasound to ensure that your IUS is still in place and has not been expelled. Some clinics will use an ultrasound device as a guide to help remove the IUS.

If the strings are not visible and all other methods have failed, you may be referred for a hysteroscopy: a procedure where a narrow telescope with a light and camera are passed into your womb through your cervix. This allows your doctor to examine the inside of your womb to locate the coil and then to remove it using forceps.

It is possible to get pregnant as soon as the Mirena is taken out, so be sure to use alternative contraception if this is not what you want

Hysteroscopic-guided removal is considered a superior and safe option to surgical removal, where ultrasound-guided removal has failed.²⁰ When deciding whether to move forward with a hysteroscopy, your doctor will consider whether you have had any previous traumatic experiences that may make the procedure difficult for you.²¹

It is possible to get pregnant as soon as the Mirena is taken out, so be sure to use alternative contraception if this is not what you want.

The decision to use the Mirena coil is different for different people, each of whom may value the various pros and cons in their own way. While it’s true that the Mirena can cause some side effects, there are also some notable benefits to the method.

Endometrial and other cancer protection

The Mirena coil has been found to have a protective effect on the lining of the womb (endometrium) from the stimulating effects of oestrogen, which prevents and causes regression of a condition called endometrial hyperplasia,²² where the endometrium becomes abnormally thick. This condition is not cancer, although people who have it may have an increased risk of developing womb cancer.²³

There is currently insufficient evidence to recommend its use as treatment for endometrial hyperplasia, but the Mirena is licensed in the UK for protection against endometrial hyperplasia in conjunction with oestrogen replacement therapy for up to 5 years.²⁴

Period and pelvic pain

While for some, the Mirena coil causes pain and cramping, in others, it has been shown to reduce period pain, along with pain due to endometriosis and adenomyosis.²⁵ There are a few theories as to why the Mirena can work to relieve endo pain: one is that it works to deplete the oestrogen and progesterone receptors in the endometrial tissue outside of the womb (so making it less “reactive”), and another is that its effects on the actual lining of the womb prevent the growth and multiplication of cells (“anti-proliferative effect”).²⁶

Heavy periods

The Mirena coil is actually licenced as a treatment for heavy menstrual bleeding and is recommended as a first-line treatment within the National Institute for Health and Care Excellence (NICE) guidelines²⁷ — national evidence-based recommendations for clinicians and other healthcare professionals. A Finnish study of 236 women in 2001 found that those with heavy menstrual bleeding had a significant improvement in their health-related quality of life due to using the Mirena.²⁸ Even people with heavy periods associated with fibroids (benign growths in uterine lining) have been shown to have lighter periods with Mirena coil.²⁹

Some people may experience side effects while using the Mirena coil. These include side effects experienced during and in the short term after insertion, and those experienced over a longer period of using the Mirena.

The below is a summary of side effects you may experience. Read a more in-depth breakdown of various Mirena coil side effects and how they are experienced.

Short-term side effects (during and after insertion) may include:

• Pain, including during insertion and cramps following insertion
• Infection — although if you test negative for infection prior to insertion, the risk of infection is negligible³⁰
• Fainting/cervical shock – this is when stimulation of the cervix (e.g. during insertion of the Mirena) causes low blood pressure. Healthcare providers will often check your blood pressure following insertion; if your blood pressure is low, they may ask you to stay lying down for a few minutes to prevent fainting
• Perforation of the uterus — this is when the Mirena makes a small hole in the wall of the uterus and is a rare occurrence. The chances of it happening are around 1 in 1000³¹
• Expulsion (where the Mirena coil falls out) — this is more likely to happen in the first three months following insertion. The risk of expulsion is 1 in 20³²

Long-term side effects and risks of the Mirena coil include:

• Hormonal side effects, including acne, breast tenderness, and headaches. There is no evidence to suggest that the Mirena causes weight gain or affects your libido³³
• Irregular bleeding and changes to periods. During the first 3-6 months of using a Mirena, you may experience changes to your period but this tends to improve over time.³⁴ In one large randomised trial, 24% of women using a Mirena coil had amenorrhoea (i.e. did not have any periods) after 3 years.³⁵

Ectopic pregnancy

The risk of becoming pregnant while using the Mirena coil is very small. However, if you do fall pregnant while using it, there is an increased chance of an ectopic pregnancy. This is where the fertilised egg implants outside of the womb, as opposed to on the endometrium (lining of the womb). Usually, a fertilised egg in an ectopic pregnancy will implant in one of the Fallopian tubes (93-98% of the time).³⁶

An ectopic pregnancy is considered serious, and prompt diagnosis is essential in reducing the risk of complications. Unfortunately, it is not possible to save the pregnancy, and your doctor will advise on the most appropriate procedure to remove the egg. This might be through use of drug treatment (usually a drug called methotrexate) or through surgery.³⁷

However, because it is so effective at preventing pregnancy, the Mirena actually reduces the overall risk of ectopic pregnancy when compared to using no contraception. The risk of ectopic pregnancy increases only if you become pregnant while using the Mirena coil, versus if you were to become pregnant without having a Mirena coil inside you.³⁸

Abortion

It is safe to have an IUS inserted immediately after abortion, although the risk of expulsion appears to be higher.³⁹ While the rate of expulsion is generally low, it has been found to be higher for second-trimester abortions than after first-trimester abortions.⁴⁰

Ovarian cysts

Functional ovarian cysts (which form as a result of the menstrual cycle) are reported as a common side effect of LNG-IUS use, however, most are asymptomatic and go away on their own.⁴¹

Should I get the Mirena coil?

It is important to weigh up the risks and benefits of any type of contraception you are considering using before making your choice. Because everyone is different, and there are many different factors that might affect the suitability of a particular method, it is essential to speak with your doctor about choosing the right contraception for you.

Your doctor may recommend a particular method but if there is a specific contraceptive you are interested in you can ask them directly if they think it would be appropriate. Taking into account your medical history and lifestyle, they will help you understand the relative pros and cons of each contraceptive method.

Featured image Sarahmirk – Own work, CC BY-SA 4.0. Image is of a white person’s hand holding out the Mirena coil. The image has been repeated to create a mirror effect, where both hands are facing the centre of the image. The hands are against a bright teal background

Page last updated January 2023
Next update due 2026