Mirena works by thickening cervical mucus, which stops sperm from reaching the egg. It also thins the uterine lining. In some women, it suppresses ovulation.
It’s used as a long-term contraceptive. Once inserted into the uterus, it can prevent pregnancy for up to five years.
Mirena is also used to treat:
- heavy periods, or menorrhagia
- chronic pelvic pain
When exploring a possible link between Mirena and breast cancer, it helps to understand the link between hormones and breast cancer.
Breast cancer can be fueled by the hormones estrogen or progesterone. Some breast cancers are fueled by HER2 proteins. Most of the time, breast cancer involves some combination of the three. Another type, triple-negative breast cancer, involves none of them.
According to BreastCancer.org, most breast cancers are hormone-positive. They are broken down into the following types:
- 80 percent of breast cancers are estrogen receptor-positive
- 65 percent are both estrogen and progesterone receptor-positive
- 13 percent are estrogen receptor-positive, but progesterone receptor-negative
- 2 percent are progesterone receptor-positive, but estrogen receptor-negative
The link between hormones and breast cancer comes down to the question of the particular synthetic hormone, and whether or not it is associated with breast cancer risk.
Reports vary about the link between breast cancer and Mirena. More research is needed for a definitive answer. Current studies point to a link between the two.
The package insert for Mirena states that if you have or have had breast cancer, or even suspect you might, you should not use hormonal contraception. It also acknowledges “spontaneous reports of breast cancer,” but says there’s not enough data to establish a link between Mirena and breast cancer.
Mirena has been on the U.S. market since 2001. It’s been the subject of a number of studies, but they’ve produced conflicting results, according to the American Cancer Society. Here are a few of those findings:
- 2005: A large post-marketing study published in the journal Obstetrics & Gynecology found that the levonorgestrel-releasing IUD is not associated with an increased risk of breast cancer.
- 2011: A retrospective, population-based, case-control study published in the journal Contraception found no increased risk of breast cancer in users of levonorgestrel-relasing IUDs.
- 2014: A large observational study published in Obstetrics & Gynecology found that levonorgestrel-releasing IUDs are associated with a higher than expected incidence of breast cancer.
- 2015: A large study published in Acta Oncologica found that use of a levonorgestrel-releasing IUD is associated with an increased risk of breast cancer.
‘But I heard that Mirena decreases your risk for breast cancer …’
There’s no evidence to suggest that Mirena lowers the risk of developing breast cancer. One reason for this confusion is that it may actually lower your risk of some other types of cancer.
In the 2014 study in Obstetrics & Gynecology mentioned above, researchers concluded that levonorgestrel-releasing IUDs are associated with a higher than expected incidence of breast cancer. That same study found a lower than expected incidence of these cancers:
Mirena is also associated with:
- lower risk of pelvic inflammatory disease (PID) caused by sexually transmitted infections (STIs)
- a decrease in pain due to endometriosis
- less menstrual pain
So, is there a link between Mirena and breast cancer?
More long-term studies are needed to correctly assess the potential link between levonorgestrel-releasing IUDs and breast cancer.
It’s important to keep in mind that there are other risk factors for breast cancer as well as other cancers. If you’re already at higher than average risk, ask your doctor if it’s safe to use any type of hormonal birth control.
Other brands of hormonal IUDs currently on the market are Liletta, Skyla, and Kyleena. All three labels carry the same warning as Mirena: that you shouldn’t use them if you currently have, previously had, or suspect breast cancer.
All acknowledge reports of breast cancer in women using hormonal IUDs. All three say there’s no conclusive evidence.
The level of hormones varies slightly with each product. Most studies investigating the link to breast cancer reference levonorgestrel-releasing IUDs in general, not specific brand names.
If you want to avoid hormones altogether, you still have the option of using an IUD. The copper T380A, marketed under the brand name ParaGard, is hormone-free. It works by triggering an immune response that creates a hostile environment for sperm.
Oral contraceptives also contain hormones. Some have estrogen, some have progestin, and some are a combination of both.
This is another area where studies are inconsistent, according to the National Cancer Institute. Overall, it appears that oral contraceptives may increase your risk of breast, cervical, and liver cancer, while decreasing your risk for endometrial and ovarian cancer.
When considering the association between hormone-based contraceptives and cancer, it’s important to remember that the risks aren’t the same for everyone. Here are a few other things that factor in to your breast cancer risk:
- family history of breast cancer
- early age at first menstruation
- later age at first pregnancy or no pregnancies
- menopause at late age
- how long you use hormone-based contraceptives
- if you’ve had hormone therapy
Discuss all your birth control options with your doctor. Here are some ideas for how to get that conversation started:
- Be sure to mention if you have a personal or family history of breast cancer or any other type of cancer.
- If you decide on an IUD, ask about the different types and the pros and cons of each. Compare the copper IUD to hormonal IUDs.
- There are many oral contraceptives to choose from. Ask about the benefits and risks of each.
- Other options include the sponge, patches, and shots. There are also diaphragms, condoms, and spermicides.
- No matter what method you ultimately choose, make sure you understand how to use it correctly.
Besides your health, you should also consider your personal preferences and how well each method fits into your lifestyle. If you choose an IUD, you’ll need a doctor to insert it and remove it, which you can have done at any time.
Everybody is different. Birth control is a personal decision. Some methods may be more reliable than others, and no method will work if you don’t use it or don’t use it correctly. That’s why it’s so important to choose something that you believe will be convenient and effective.
If you’re looking for long-term birth control that you don’t have to think about in the moment, Mirena is one option to consider. If you have any health concerns about using it, discuss them with your doctor before making your decision.