Mirena™ information sheet

What is the Mirena™ intrauterine system?

The Mirena™ intrauterine system (you may also know it as a ‘hormone coil’) is a small T-shaped, plastic device that is fitted into the womb. There are different types of intrauterine systems, but the Mirena™ is particularly useful. This is because, in addition to it being a form of contraception, it can also be used as part of your hormone replacement therapy (HRT).

Using the Mirena ™ as part of your HRT

HRT consists of two hormones – oestrogen and progestogen. Oestrogen manages most menopause symptoms, and progestogen protects the lining of the womb. That’s because if you still have a womb (you haven’t had a hysterectomy) and you take oestrogen by itself, it can thicken the lining of your womb, increasing your risk of womb cancer. Progestogen prevents the lining of your womb from thickening.

Once a Mirena™ has been fitted, it lasts for 5 years (this use is outside its product license – but is used in line with guidance from the Faculty of Sexual and Reproductive Healthcare). If you have a Mirena™ fitted, you only need to take oestrogen, which can come in a patch, gel, spray, or tablet.

Where can I get it fitted?

Many GPs and nurses fit Mirena™ and you can usually get this done at your GP practice or a local sexual health clinic. Before you have the Mirena™ fitted, you need to make sure that you aren’t pregnant and/or don’t have any sexually transmitted infections (STIs). If you’re at risk of an STI, the nurse or doctor will take a swab, or you may be given antibiotics at the time of fitting.

How is it fitted?

Having a Mirena™ fitted takes around 5-10 minutes, though your appointment will usually be longer than that.

You can sometimes (but not always) experience intense, short-lasting period-like pains during fitting, and you may get some period-like cramps over the next few days.

 A doctor or nurse will first examine you internally and then use a speculum to see the cervix (this feels a bit like having a smear).

The Mirena™ comes folded in a slim ‘introducer’, which is passed through the neck of the womb (cervix) and released into the cavity. Two thin threads are left hanging into the vagina. A medical professional uses the threads to remove the coil. You may be able to check the threads are present – particularly initially, but with time the threads curl over the neck of the womb and so you may not be able to feel them. Your partner should not be able to feel the threads during sex. If they are felt during sex, please see a doctor or nurse to check the fitting and trim the threads if needed.

What are the advantages?

• You only absorb a tiny amount of progestogen into your body. Some women tolerate this better than progestogen tablets.
• Most women have significantly lighter periods or no periods at all.
• A Mirena™ can help make periods less painful.
• You don’t have to remember to take a tablet.
• It’s very effective contraception – less than 1 in 100 women will become pregnant if the Mirena™ is correctly fitted.
• It’s usually easy to remove.
• It’s not affected by other medicines.
• If you’re using it for contraception alone (and not as part of HRT), and if you have it fitted after the age of 45, you can use it till you’re through the menopause for contraception. If you’re using it as part of HRT too, you must have it changed or use an alternative progestogen, after 5 years.
• The Mirena™ shouldn’t affect your sex drive.

What are the disadvantages?

• The main disadvantage of the Mirena™ is that sometimes it’s not possible to fit one because the channel through the cervix is very narrow or because there may be fibroids obstructing the passage of the Mirena™.
• In the first 3-6 months after you have a Mirena™ fitted, it’s common to have some irregular bleeding, which can be annoying.
• Some women may get side effects, such as acne, headaches, and breast tenderness, though any side effects usually settle in the first few months.
• Occasionally, some women are very intolerant to progestogen, and it can cause low mood or anxiety.
• Very occasionally, the Mirena™ can become dislodged or come out. Checking that you can feel the threads in the vagina is a way to ensure that the Mirena™ is still where it is meant to be. Contact a doctor if you have any doubts and use additional contraception (such as condoms) if you’re using it for that reason.
• While it is being fitted, there’s a very small risk – around 2 in 1000 insertions – of making a very small hole in the wall of the womb (more information can be found here: https://www.fsrh.org/standards-and-guidance/documents/ceuguidanceintrauterinecontraception/). This is why it’s important that a trained doctor or nurse fits the Mirena™. If there were a chance that a perforation had happened, you would need to have an ultrasound or X-ray and, in a worst-case scenario, an operation to retrieve the coil.
• The risk of getting cysts (fluid-filled sacs) of the ovary is greater when you have a Mirena™. They are usually harmless, don’t cause symptoms, and go away by themselves.
• You are at the most risk of getting an infection in the first few weeks after having your Mirena™ fitted.

If you’ve had a Mirena™ fitted, you should always see a doctor if you develop a fever, abnormal or offensive vaginal discharge (as a sign of infection), pelvic pain, abnormal vaginal bleeding (more than the expected frequent spotting), if you suspect pregnancy or if you cannot feel the threads, or you can feel the hard plastic stem of the Mirena™ in the vagina.

For more information:

• https://www.fsrh.org/standards-and-guidance/documents/ceuguidanceintrauterinecontraception/
• https://www.medicines.org.uk/emc/files/pil.1132.pdf

If you would like a Mirena™ fitted, the best first port of call would be your GP practice or local sexual health clinic.