by Ros Wood

The Mirena coil is a small plastic T-shaped intrauterine device that is increasingly being used to treat women with endometriosis. It contains a progestogen (progesterone-like substance) that is released into the uterus over a period of 5 years. It is sometimes also known by its generic name the levongorgestrel intrauterine system or LNG-IUS.

Mirena has been used around the world as a contraceptive since the early 1990s. However, it is only in the last few years that gynaecologists have begun investigating its possible use for the treatment of endometriosis, even though it has not been approved for this use in most countries.

Little information is available on the use of Mirena for women with endometriosis. Only a few studies have been published, the longest of which followed women for 3 years. However, to date, the studies indicate that it is an effective treatment for endometriosis, and may have the potential to be a long-term treatment for women who want to postpone pregnancy.

If Mirena proves to be an effective long-term treatment, it offers several potential advantages over current treatments: theoretically fewer side effects, no need to take tablets every day or have regular injections, no need for contraception, and the option of continuous treatment that avoids the roller-coaster of alternating short-term treatments and recurrences.

However, more well designed clinical trials are needed before its true role can be determined.

How it works

It is not known precisely how progestins relieve the symptoms of endometriosis, but they probably work by suppressing the growth of endometrial implants in some way, causing them to gradually waste away [3]. They may also reduce endometriosis-induced inflammation in the pelvic cavity [4].

At the dosages usually used for endometriosis, most women will stop ovulating and menstruating during treatment. The levonorgestrel intrauterine system does not always stop ovulation.

In the first 3–6 months, many women will experience spotting, but some may experience heavy or prolonged bleeding. Later, most women will have lighter periods than previously, and some will have no periods.

Most women will resume ovulating and menstruating within 4–6 weeks of stopping treatment. With depot medroxyprogesterone acetate, women will not start ovulating and menstruating again until after the drug has been completely removed from their bodies. How long this takes will depend on the dose used and how rapidly their body metabolises the drug.

Women who have had long-acting injections may experience prolonged delays in the return of menstruation, and a few women may not menstruate for more than a year after their last injection. Therefore, it is recommended that you do not use depot medroxyprogesterone acetate if you may wish to become pregnant soon after treatment.


Before inserting a Mirena coil, your doctor will conduct a thorough examination to make sure you do not have any problems that would prevent you using the coil.

You should not have a coil inserted if you are or suspect that you may be pregnant. Also, you should not have a coil inserted within 6 weeks of having vaginal birth or within 12 weeks of having a caesarean birth, because there is greater chance that the coil will perforate (protrude through) the uterus if you do so.

It is also vital that you have not had a genital infection in the 3 months before fitting.

Some gynaecologists are hesitant to insert a Mirena coil in women who have not had children, because their smaller uteri may result in more problems with uterine cramping.

The Mirena coil can be fitted in the gynaecologist’s rooms, or during a laparoscopy if you have given your permission beforehand.

You may feel some discomfort while the coil is being inserted, and you may feel some cramping for up to a few hours afterwards, particularly if you have not given birth previously. You may also feel a little faint afterwards, but this is normal and you just need to rest for a while.

It is recommended that you do not have sexual intercourse for 24 hours after having the coil inserted.
When the coil is in place, you should not be able to feel it, and it is unlikely that your sexual partner will be aware of it during intercourse.

The Mirena coil lasts for 5 years, after which you can have it replaced. The coil can be removed at any time. To remove the coil, the gynaecologist pulls on the strings during a gynaecological examination. Usually, removal is uncomfortable for only a second or two.

Side effects

In the longest clinical trial reported to date, the women had relatively few side effects, and most of the side effects were quite mild. Of the women who had their coil removed because of side effects, most did so because of irregular bleeding, pelvic pain or weight gain, and most did so in the first 12 months.

Irregular bleeding
Most common side effect of Mirena is irregular vaginal bleeding, which includes erratic bleeding, frequent spotting or light bleeding between periods, heavy bleeding, and longer or shorter periods. However, these problems usually settle after 3–6 months.

Progestogen-related symptoms
Although the levongorgestrel in the coil is released into the uterus, a small amount is absorbed into the bloodstream. The amount of levongorgestrel in the blood is about one-seventh of that found in women using the oral contraceptive pill, so fewer women experience side effects than with the other progestogen treatments for endometriosis (oral contraceptive pill, Duphaston, Provera, etc). If side effects do occur, they are usually quite mild and tolerable, and they often disappear after 4–6 weeks.

The progestogen-related side effects include:

  • acne
  • decreased libido
  • headache
  • lower abdominal pain
  • low back pain
  • nausea
  • period pain
  • sweating
  • tender breasts
  • water retention
  • weight gain.

Ovarian cysts
Women using the Mirena coil are more likely to develop benign ‘simple’ ovarian cysts. The most common symptom of a simple cyst is abdominal pain that does not resolve with simple painkillers. Such cysts usually disappear without treatment in 2–3 months.

Pelvic infection
The Mirena coil system is designed to minimise the risk of infection, but there is still a slight risk of developing a pelvic infection while using the coil, particularly in the first 3 weeks after insertion. Such infections are usually related to sexually transmitted diseases, and you are more likely to develop an infection if you or your partner has several sexual partners. Overall, about 1.5% of women will develop an infection with 5 years use of the coil. You can reduce your risk of developing an infection by using a condom when having sex with anybody other than your long-term sexual partner.

If you develop a pelvic infection, it must be treated promptly. Contact your doctor immediately if you begin experiencing persistent lower abdominal pain, fever, pain with intercourse or abnormal bleeding as these symptoms may indicate a pelvic infection.

If you develop a pelvic infection, the coil should be removed.

Effectiveness for pain symptoms

Several small clinical trials have investigated the effectiveness of the Mirena coil for the treatment of endometriosis. The results to date indicate that it reduces period pain over 3 years, with most of the improvement being in the first 12–18 months. However, whether the improvement in symptoms would continue for the entire 5 year life of the coil is not known.

The only trial that compared use of the Mirena coil with a GnRH agonist found that both treatments were equally effective in relieving endometriosis pain over a 6 month treatment.

Effectiveness for infertility

Like all the hormonal treatments for endometriosis, the Mirena coil should not be used to treat infertility.

Keeping track

Visit gynaecologist
You should visit your gynaecologist about 6 weeks after having the Mirena coil inserted, and every 12 months thereafter.

Check in place
In about 5% of women, the muscular contractions of the uterus push the coil out of place or expel it from the uterus. This is most likely to occur in the first few months after insertion.

Each month, you should check that the coil is in place by feeling for the two fine black threads hanging from its base. If you cannot feel the threads, contact your doctor.

If the Mirena coil has been dislodged, you may be able to feel the lower end of the device, or you may experience persistent pain or abnormal bleeding, or you or your partner may feel pain or discomfort during intercourse. If the coil has been expelled, you may not be aware of the expulsion initially, but later you will probably experience changes in your bleeding pattern and eventually a return to your previous bleeding pattern. If you have any signs of dislodgement or expulsion, contact your gynaecologist immediately.

Don’t ever pull on the threads, because you may accidentally pull out the device.

Pregnancy and breastfeeding

You should not have a coil inserted if you are or may be pregnant.

The coil is a long-term contraceptive device with a low failure rate. Nevertheless, if there is any possibility that you may have become pregnant while using the device, contact your doctor so the device can be removed.

Small amounts of progestogens have been found in the milk of mothers using Mirena. The amounts are similar to that found in the milk of mothers taking the progestogen-only mini pill. Extensive experience of breastfeeding while on the mini pill indicates that it has no harmful effects on the baby.


Mirena does not interact with other drugs, foods or alcohol.

  1. Lockhat FB, Emembolu JO, and Konje JC. The evaluation of the effectiveness of an intrauterine-administered progestogen (levonorgestrel) in the symptomatic treatment of endometriosis and in the staging of the disease. Hum Reprod 2004;19:179-184.
  2. Lockhat FB, Emembolu JO, and Konje JC. The efficacy, side-effects and continuation rates in women with symptomatic endometriosis undergoing treatment with an intra-uterine administered progestogen (levonorgestrel): a 3 year follow-up. Hum Reprod 2005;20:789-793.
  3. Petta CA, Ferriani RA, Abrao MS, Hassan D, Rosa E Silva JC, Podgaec S, and Bahamondes L. Randomized clinical trial of a levonorgestrel-releasing intrauterine system and a depot GnRH analogue for the treatment of chronic pelvic pain in women with endometriosis. Hum Reprod 2005;20:1993-1998.
  4. Varma R, Sinha D, and Gupta JK. Non-contraceptive uses of levonorgestrel-releasing hormone system (LNG-IUS)-A systematic enquiry and overview. Eur J Obstet Gynecol Reprod Biol 2006;125(1):9-28.
  5. Vercellini P, Aimi G, Panazza S, De GO, Pesole A and Crosignani PG. A levonorgestrel-releasing intrauterine system for the treatment of dysmenorrhea associated with endometriosis: a pilot study. Fertil Steril 1999;72:505-508.
Thank you to the following for reviewing this article prior to its publication

Michael East, Consultant Gynaecologist, Oxford Clinic, Christchurch, New Zealand
Andrew Prentice, University Senior Lecturer and Consultant Gynaecologist, Cambridge University, UK
Paolo Vercellini, Associate Professor, University of Milano, Italy

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