What is Mirena&Reg;?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 06 January 2020
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Mirena® is an intrauterine (inside the uterus) device or IUD, that is primarily used to prevent unwanted pregnancy. Unlike the copper IUD called the ParaGuard®, Mirena® combines the benefits of IUD protection with low dose hormones, which may provide additional protection against pregnancy. Due to the fact that this IUD or intrauterine system does have hormones (progestin), it has different recommendations for use than ParaGuard®, though many women can choose either one as a reliable birth control device.

There are several ways Mirena® works. The irritation to the cervix produced by having a foreign device in it creates an increase in cervical mucus. This mucus tends to block sperm, and actually may kill it. Incidence of ovulation occurs with less frequency, due to hormone release, so chances of getting pregnant are reduced. The lining of the uterus is also thinned, which may make it difficult for fertilized eggs to implant.

The actual Mirena® device requires insertion in a doctor's office. The small T-shaped device is inserted through the cervix. For most women this is at least mildly uncomfortable, and may be helped by using an over the counter pain reliever before the procedure. Timing the insertion at different points in a women’s cycle may make a difference in how much insertion is felt, and women who have had children vaginally typically have less discomfort.


Once the device is in place, women can feel small threads that extrude from the cervix. They are instructed to manually examine these threads each month after menstruation, and to see a doctor if they cannot find the threads, or if the threads are longer. Some women do expel the device, and this is more common in women who have not previously had children, though incidence is still rare, at about 4%.

Potential complications from insertion include that it can perforate the uterus. Pregnancy may still result, though it is extremely rare, when the device is in place. Pregnancies occurring have higher likelihood of being ectopic and removal of the device during pregnancy hazards risk for miscarriage. There is no birth control device that doesn’t have some risk of pregnancy however, and all IUDs are considered some of the most effective methods, with risk of pregnancy below 1-2%. IUDs don’t prevent sexual transmitted diseases, though, and women who are not in stable relationships with a single partner may be advised to still use condoms or to consider other birth control methods.

When Mirena® is tolerated, the device can remain in place for up to 5 years, or it can be removed in a doctor’s office if a woman would like to become pregnant or if the device is causing problems. It usually does result in shorter periods, though some women might have long and very heavy periods and may become anemic, requiring removal sooner. On the other hand, some women may use this device specifically to shorten periods and cure heavy bleeding.

There are some people who should not use Mirena®. These include those who have pelvic inflammatory disease or a history of breast or ovarian cancer, smokers over the age of 35, people with AIDs or hepatitis, anyone with deep vein thrombosis, and those with active uterine infections or with other types of STDs. It’s important to discuss all risks and benefits of using an IUD with skilled physician, and be able to give a detailed medical history in order to determine if an IUD is the right choice.



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