Mirena is contraceptive device known as intrauterine system (or IUS) developed and supplied by Bayer pharmaceutical company. It is a small plastic device in the shape of a letter T that is placed inside the vagina by a trained nurse or physician. Once inserted, it can remain there for as much as five years, while slowly releasing measured doses of active ingredient, synthetic hormone levonorgestrel which can efficiently mimic the activity of naturally-occurring sex hormone progesterone. As such, Mirena coil will work in almost the same way as hormonal contraceptive pills or patches.

What’s on this page?

With a one-time application, Mirena coil is highly efficient and it will not only provide a very high level of protection from unwanted pregnancy, but will also provide relief from heavy periods.

What is the role of levonorgestrel?

Sex hormones progesterone and oestrogen play crucial role in the monthly cycle the female body goes through each month in order to prepare itself for potential pregnancy. Progesterone is probably the more important of the two as it guides and triggers the release of the egg cells from the ovaries to the fallopian tubes where they can get fertilised. It also contributes to the build-up along the uterine wall, allowing the fertilised egg cell to implant successfully.

So, it comes as no surprise that pharmaceutical compounds that are highly adept at mimicking the activity of this sex hormone can interfere with the process and delay ovulation, indefinitely if needed, provided that there is a steady supply of the synthetic hormone.

How does Mirena work?

The mechanism of action described above is at the core of Mirena’s efficiency at preventing pregnancy. By releasing levonorgestrel, it will supplement the falling levels of progesterone which will in turn send a “signal” to the ovaries that it is not yet time for ovulation, so the egg cells won’t be released and conception will not be possible.

At the same time, this hormone will prevent the thickening of the uterine wall (known among the medical experts as endometrium), thus making it more difficult for the egg to implant. Finally, it will also contribute to the thickening of the cervical mucus which will make it much more difficult for the sperm to reach the egg cell. With this multidimensional approach, Mirena coil can successfully prevent pregnancy over the whole course of its activity.

How reliable is Mirena?

Mirena is one of the only two branded IUSs which can be obtained in the UK which testifies to its safety and reliability. It is highly efficient for as long as you avoid certain compounds, foodstuffs and medications which might impair its functionality. If there is no choice but to use some of those problematic medications, you should just use additional barrier contraception until the Mirena protection levels are back to their optimal values.

The problematic substances in question include:

  • Antiepileptics
  • Tuberculosis medications
  • HIV or AIDS medications
  • Antibiotics
  • St John’s wort
  • Cyclosporine

How can I get Mirena coil placed?

As was mentioned, you cannot apply Mirena coil by yourself and only a trained nurse or doctor can do it in a clinical setting. Prior to the procedure, you will be required to undergo certain checks and tests in order to help the doctor team make sure that Mirena is a safe option for you and there will be no subsequent complications.

However, just like with more conventional medications, Mirena will also come with official patient information leaflet and there you will be able to find all the relevant information regarding this procedure, but also regarding steps you should take to ensure maximum efficiency of this IUS.

What are Mirena side effects?

Despite being an intrauterine system, Mirena coil comes with potential for certain side effects, just like more conventional contraceptive pills. And just like with them, any signs of an allergic reaction should be treated as a cause for concern and you should report them to your doctor right away. Other worrisome side effects include:

  • Severe pain or fever after insertion
  • Prolonged bleeding
  • Pain in the lower abdomen
  • Unexpected bleedings
  • Pain during intercourse

Other documented side effects can be uncomfortable, but not really dangerous and they include:

Frequency of occurrence Side effects
Very common (1 in 10 women or more) Vaginal bleeding and spotting, infrequent menstrual periods, lighter menstrual periods
Common (1 in 10 women or less) Increased period pain, ovarian cysts, weight fluctuations, mood swings, headaches and migraines, pelvic pain, pain in the lower back, nausea, acne, increased hair growth, loss of libido, inflammation of the vagina, vaginal discharge, breast pain
Uncommon (1 in 100 women) Infection or inflammation of the neck of the womb, swelling of the abdomen, legs or ankles, hair loss, eczema, chloasma
Rare (1 in 1000 women) Skin rashes


Please note that this is not a complete list of all documented side effects. For a more comprehensive overview, please refer to the Mirena official patient information leaflet or consult your doctor.