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Mirena is a long-acting, reversible birth control implant called a hormonal intrauterine device (IUD) manufactured by Bayer Pharmaceuticals. An IUD is a small, flexible, T-shaped device that doctors implant in the uterus. Mirena uses levonorgestrel — a progestin birth control hormone — to prevent pregnancy. It releases a small amount of hormones into the uterus over time.

*Please seek the advice of a medical professional before discontinuing the use of this medical device.

Mirena IUD
Mirena IUD xray
Xray showing a Mirena IUD

The Food and Drug Administration (FDA) approved Mirena in 2000. In 2009, the FDA expanded Mirena’s approval to treat heavy menstrual bleeding in women already using an IUD. It is more than 99 percent effective in controlling pregnancy for up to 5 years. After 5 years, women should replace the IUD.  Doctors recommend Mirena for women who have had at least one child.

Globally, the IUD is the most popular form of reversible birth control with an estimated 150 million users. In the United States, the IUD’s popularity is growing and it made up about 10.4 percent of the contraceptives issued by doctors in 2011, up from 1.4 percent in 2002. About 2 million women use Mirena in the U.S.

Medical providers insert Mirena, and it usually costs about $800. Depending on insurance coverage, the cost may vary.

Bayer markets Mirena as more convenient and effective than most oral contraceptives. Once doctors implant the IUD, women don’t have to worry about taking a daily pill. The effectiveness of oral contraception relies on “perfect use,” meaning women must faithfully take their birth control daily. Oral contraceptives have a failure rate as high as 30 percent because women may forget to take the pill, while Mirena has a failure rate of less than 1 percent.

Despite Mirena’s effectiveness and ease of use, it is not without side effects.

How Does Mirena Work?

Mirena works by slowly releasing 20 mcg of levonorgestrel into the uterus each day. Throughout the course of 5 years, this dose decreases while effectively preventing pregnancy. In contrast, birth control pills typically release 150 mcg into the body. Oral contraceptives have a higher dose of hormones because they pass through the digestive tract before acting on the uterus. Mirena works by directly releasing the hormone into the uterus.

Because Mirena thins the lining of the uterus, it also decreases menstrual bleeding. After women receive the implant, women don’t need to do anything to prevent pregnancy for up to 5 years.

While Bayer doesn’t know the exact way Mirena works, it may work in one or more of the following ways:

  • Thickening the mucus on the cervical wall to prevent sperm from entering the uterus
  • Altering the wall of the uterus
  • Inhibiting survival of sperm

Mirena IUD Insertion

The Mirena intrauterine system includes a T-shaped body made from medical grade, polyethylene plastic, and a cylinder-shaped steroid reservoir that covers the vertical piece of the T.The steroid reservoir is made of silicone and 52 mg of levonorgestrel. This is the progestin hormone and active ingredient. Over time, the reservoir releases hormones into the uterus.

Mirena IUD upclose
Mirena IUD upclose

Mirena comes with a sterile insert applicator. Both the horizontal and vertical pieces of the T are 32mm in length, or about the size of a matchstick. At the end of the vertical piece, there is a small loop with attached polyethylene strings. These strings are for IUD removal.

The doctor or health care professional will perform an examination of the uterus to make sure it is safe to implant the device. Only a qualified health care professional should implant the IUD. The device slides into the uterus through the cylindrical sterile inserter. The horizontal part of the T (the arms) anchors the Mirena inside the uterus.

The doctor will trim the strings to an appropriate length for each patient, so the exact length can vary. Women should check the strings every month to ensure the IUD is still in place.
The examination, preparation and insertion take about 30 minutes. Some women may experience discomfort during the insertion, including cramps and feeling faint and nauseated.

Removing Mirena

The health care provider removes Mirena by using the attached string. The arms of the device are flexible and bend up when the device come out. However, sometimes the device can migrate outside of the uterus or become lodged in the uterine wall. When this happens, doctors must remove the device surgically.

Clinical Studies

In two large clinical trials, Mirena proved to be extremely effective in preventing pregnancy. In the studies, 1,169 women 18-35 years of age used Mirena for up to 5 years. The pregnancy rate over the 5 years was 0.7 per 100 women, or 0.7 percent. About 80 percent of women who wanted to become pregnant were able to do so within a year after removing Mirena.

Mirena clinical study statistics

Side Effects of Mirena

In clinical trials, researchers compared Mirena to a copper IUD and a combined oral contraceptive in women 18 to 35 years of age. For women using Mirena to control heavy periods, researchers studied women ages 26 to 50.

Common side effects of Mirena include:

  • Acne
  • Weight change
  • Mood changes
  • Breast tenderness
  • Nausea
  • Ovarian cysts
  • Vaginal discharge
  • Abnormal bleeding patterns

Mirena and Weight Gain

Weight gain is a concern of most women who use hormonal birth control. It is one of the listed side effects of Mirena. In clinical studies, less than 5 percent of women gained weight on Mirena.

In other studies of progestin-only birth control methods, including Mirena, there was little evidence of substantial weight gain.

In one medical review published in August 2016 in the Cochrane Library by Laureen M. Lopez and colleagues, researchers looked at 22 studies that included 11,450 women. The goal of the literature review was to study progestin-only birth control and changes in body weight.

Researchers found the average weight gain was 4.4 pounds at 6 or 12 months for most studies.

Pregnancy Risks & Other Serious Side Effects

Mirena is highly effective at preventing pregnancy, but some women may experience dangerous, life-threatening side effects such as perforation of the uterus, pelvic inflammatory disease and ectopic pregnancy (pregnancy that occurs outside the uterus). The device may also spontaneously move from the uterus and embed in other parts of the body such as the uterine wall or abdomen, requiring difficult surgery to remove.

Device Migration

One of the most dangerous side effects of Mirena occurs when the device migrates from its normal position in the uterus. Despite the fact that Bayer claims this is a rare occurrence with Mirena, a study published by the Department of Radiology at the Ronald Reagan UCLA Medical Center found that this is a “frequently encountered complication.”


IUDs migrate and can perforate the uterus and enter the abdominal cavity, pelvis, bladder or blood vessels.

When the IUD migrates, it can perforate the uterus and enter the abdominal cavity, pelvis, bladder or blood vessels. It can cause pain, infection, and damage to intestines and other nearby organs. This is a serious condition and requires surgery to correct. In some cases, emergency surgery is necessary to prevent further damage.

In order to locate the device, radiologists use an ultrasound or X-ray. In some cases, women have had to undergo several surgeries because the device is difficult to locate and remove. The risk of perforation of the uterus is also increased in women who use Mirena immediately after delivering a child, and the risk is elevated for at least 6 months after delivery.

Pregnancy complications

If a woman becomes pregnant with Mirena, doctors recommend surgically removing the zygote immediately. Otherwise, the patient can experience a septic abortion, a condition in which the uterus becomes septic, endangering both the patient and the pregnancy. Mirena can also cause miscarriage, premature delivery and sepsis.

Ectopic pregnancy

Of the women who become pregnant while using Mirena, half are ectopic pregnancies, which occur when an egg becomes fertilized outside of the uterus. It is often referred to as a “tubal pregnancy,” since it commonly occurs within one of the fallopian tubes. An ectopic pregnancy threatens the life of the mother. Women who have ectopic pregnancies often undergo surgery to remove the fertilized egg (zygote) and may become infertile.

Pelvic inflammatory disease

A bacterial infection that affects the female reproductive system can often result in pelvic inflammatory disease (PID). PID can cause infertility by damaging the uterus, ovaries and fallopian tubes. This condition can occur within three weeks after insertion of Mirena. The FDA warns that women with a history of PID should avoid Mirena and all IUDs.

Device expulsion

The body may spontaneously expel the device. During this time, the woman is unprotected from pregnancy. This occurs in about 6 percent of Mirena users. Some symptoms of a possible device expulsion include cramping, bleeding or spotting, pain during sexual intercourse and lengthened or absent device strings. Women who have never given birth are at higher risk for device expulsion.

Pseudotumor Cerebri & Intracranial Hypertension

Studies also link Mirena to an increase of pressure inside the skull called idiopathic intracranial hypertension, also called pseudotumor cerebri because symptoms mimic a brain tumor. It is most common in women of childbearing age.


Symptoms of this condition include nausea, dizziness, blurred or dimmed vision, ringing in ears, seeing light flashes and moderate to severe headaches.

Case studies as early as one published in 1995 in the New England Journal of Medicine show an association between levonorgestrel implants and intracranial hypertension. Dr. John B. Alder and colleagues reported on the cases of two women who were 16 and 19 years old. They were in general good health. They reported severe headaches and vision problems. Researchers recommended removing the IUD if intracranial pressure increases.

The FDA and Mirena

Bayer has also had problems with the FDA regarding Mirena. In reviewing the manufacturer’s script for advertising for the product, the FDA warned Bayer in a Dec. 30, 2009, letter that the company was in violation of the Federal Food, Drug, and Cosmetic Act.

Bayer HealthCare building
Bayer Healthcare Building

The agency further stated that the advertising included false or misleading presentations and misbranded the drug. According to the FDA, Bayer made false claims that the use of Mirena will result in “increased levels of intimacy, romance and by implication emotional satisfaction” when there is no evidence for this claim.

In addition, Bayer falsely insinuated that women who use Mirena will “look and feel great,” even though women using the product may experience weight gain, back pain, breast pain and acne. The advertising also omits important instructions with regard to the use of the device. The FDA has also warned Bayer for omitting risk information for complications.

Drugwatch.com Author


Michelle Llamas is a writer and researcher for Drugwatch.com. She is also the host of Drugwatch Podcast and has appeared as a guest on podcasts and radio shows.

View Sources
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