Mirena is an intrauterine device that releases levonorgestrel, a synthetic form of the hormone progesterone. Women take it for contraceptive and medical purposes. Some studies link the device to breast cancer, although, there is a need for more research to confirm this.
The Mirena intrauterine device (IUD) works by thickening the mucus in the cervix. This prevents sperm from reaching the eggs that ovaries release.
It also makes the uterine walls thinner, which partially suppresses ovulation for some women. For this reason, the Mirena IUD can help a woman manage heavy menstrual bleeding and other hormone related health problems.
In this article, we present the research behind the possible link between the Mirena IUD and breast cancer, as well as looking at other IUDs and their potential risks.
The most recent label information from the U.S. Food and Drug Administration (FDA) acknowledges a potential breast cancer risk for women who use the Mirena IUD, stating:
"Women who currently have or have had breast cancer, or suspect breast cancer, should not use hormonal contraception because some breast cancers are hormone-sensitive."
However, the label goes on to note that research studies on the increased risk are not definite, advising the following:
"Observational studies of the risk of breast cancer with use of a LNG-releasing IUS do not provide conclusive evidence of increased risk."
Research that found no link
Mirena has been available for more than 15 years. Research has not yet provided a conclusive answer about its possible link to breast cancer.
One of the earliest studies about a link between Mirena and breast cancer appeared in the journal Obstetrics & Gynecology in 2005. The results of that study concluded that there was not an association between the use of Mirena and increased breast cancer risk.
Another study from 2011 in the journal Contraception also did not find an increased risk of breast cancer in people using Mirena.
Research suggesting a link
A 2014 observational study in Obstetrics & Gynecology looked at women aged 30–49 years from Finland who used the Mirena IUD to control heavy menstrual bleeding.
The findings showed that Mirena decreased the risk of endometrial, ovarian, pancreatic, and lung cancers. However, the study reported a higher incidence of breast cancer than the researchers expected.
The journal Acta Oncologica published a large study in 2015 that also found a connection between the increased risk of breast cancer and Mirena use.
A 2016 systematic review in Breast Cancer Research and Treatment did not associate progestin-only birth control with a higher incidence of breast cancer. However, the researchers noted that small sample size limited most of the studies, and there was a need for scientists to do further research.
More studies are necessary to help medical professionals better understand the effects of synthetic progesterone on women when they are prescribing a Mirena IUD.
Post Reproductive Health published a more recent review in 2017. It stated that the risk of breast cancer that hormonal contraception induced is relatively low and that the benefits of contraceptives may outweigh the risks. However, again, the review said the limited evidence should not imply safety.
There do not appear to be any research studies indicating an increased risk of breast cancer from using the ParaGard IUD (copper IUD), which does not release hormones. If women want to avoid hormonal birth control altogether, ParaGard might be a more suitable option.
Several studies, including a 2017 review in the journal Evolution, Medicine, and Public Health, have reported an increase in the incidence of breast cancer in women who use hormonal oral birth control.
The review considered data from 12 separate studies on hormonal birth control that contained serum estradiol and progesterone. The age range of those using the contraceptive was 19–40 years.
The researchers found that the participants' breast cancer risk was higher after exposure to these hormones. However, they only linked their results to the types of hormonal birth control under investigation and were unaware of any increased risks associated with other hormonal birth control methods.
The level of hormones depends on the product, so it is sensible for women to discuss their concerns with a doctor to determine whether any risks outweigh the benefits.
While research has been inconclusive, it suggests that the Mirena coil is unlikely to significantly increase a woman's breast cancer risk in those who do not already have a high risk.
Birth control is a personal choice. While some methods might be more reliable than others, it is essential to use birth control safely. A key factor in choosing birth control should be its effectiveness and suitability for individual lives.
When making a decision, a woman should seek consultation with her doctor about any health concerns so that the doctor can help her determine the best option.
Are there situations where I will medically require a Mirena coil, and are there no alternatives? I experience heavy menstrual bleeding but have a high risk of breast cancer.
Studies have found that Mirena (or a progestin-releasing coil device) is more effective than oral tablets for treating heavy menstrual bleeding.
Doctors do not typically recommend Paragard, or the copper IUD, which is nonhormonal, for treating heavy menstrual bleeding. However, other alternatives such as surgery to remove the uterus or the uterine lining are options, though they are more invasive and costly.
It’s best to discuss the right option for treating heavy menstrual bleeding with your doctor.Yamini Ranchod, PhD, MS Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.