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Mirena IUD - a harmless device?

The levonorgestrel intrauterine device (IUD) is a form of long-acting reversible contraception (LARC) that is inserted into the uterus to prevent pregnancy. It is a small, T-shaped plastic device that releases the hormone levonorgestrel into the uterus over a period of time. Levonorgestrel is a synthetic progestin, which is a type of hormone similar to the natural hormone progesterone.

Here's how the levonorgestrel IUD works:

  1. Prevents sperm from reaching the egg: Levonorgestrel thickens the cervical mucus, making it difficult for sperm to swim through the cervix and reach the egg in the fallopian tubes. This reduces the chances of fertilization.

  2. Inhibits ovulation: In some cases, levonorgestrel may also suppress ovulation, preventing the release of eggs from the ovaries. This further reduces the likelihood of pregnancy.

  3. Thins the uterine lining: Levonorgestrel can thin the lining of the uterus, making it less suitable for implantation of a fertilized egg. If fertilization does occur, the fertilized egg may have difficulty implanting and developing, leading to a reduced risk of pregnancy.


In addition to its contraceptive benefits, the levonorgestrel IUD may also offer other advantages such as reducing menstrual bleeding and cramping for some individuals.



It has long been postulated that IUDs only release progestins locally in the uterline lining. However, several studies have shown that the synthetic progestins have systemic absorption, hence why ovulation can be suppressed.


Some studies have suggested a slight increase in the risk of breast cancer among users of hormonal contraceptives, including levonorgestrel IUDs regardless of age and indication. The effect of LNG-IUS on breast cancer risk seems to be larger in older users. The odds ratio was found to be 1.16 in women of all ages; for women aged <50 years it was 1.12 ; and for women aged ≥50 years it was 1.52. An odds ratio of 1.16 suggests that the odds of breast cancer happening are 1.16 times higher in the IUD group compared to women who had never used the IUD.


Christiane Kuhl, M.D., a leading breast cancer researcher and chief of the Department of Radiology at RWTH Aachen University noticed that women with a hormonal IUD in place often show higher background parenchymal enhancement on contrast-enhanced breast MRI. Background parenchymal enhancement —the initial enhancement of normal breast tissue—is a sensitive marker of hormone levels. Half of the women in the study underwent the first breast MRI exam before IUD placement and the second with the IUD in place. The other half had their first MRI with IUD placement and the second MRI after IUD removal. This enabled the researchers to avoid age-related effects on background parenchymal enhancement that might affect interpretation of the results. Analysis showed that IUD use led to significant increase of enhancement in 23 of 48 patients, indicating that there are hormonal effects caused by IUD use that occur well beyond the uterus.


Furthermore, the levonorgestrel in IUDs has androgenic effects and can cause acne, hair thinning and hair growth in the face. Other studies have reported psychiatric symptoms associated with LNG-IUDs, predominantly depression.


Before making a decision to get an IUD, make sure you weigh all risks and benefits with your doctor.


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