Mirena is a type of intrauterine devices (IUD) that prevents pregnancy for up to 5 years. It works by releasing a hormone called levonorgestrel, a type of progestin. Because of this, Mirena may not be the best choice if you have a history of breast cancer that is sensitive to progestin. But for most women, it's a very safe and effective choice.
The connection between birth control and breast cancer isn’t unique to Mirena. All hormonal contraception could slightly raise your odds of breast cancer.
That’s because the hormones estrogen and progesterone fuel certain breast cancers. Hormonal birth control contains man-made (synthetic) versions of one or both of these hormones. Progestin, the hormone in Mirena, is a man-made form of progesterone.
Don’t panic if you’re on hormonal birth control, though. Studies show again and again that the increased chance of breast cancer is small.
IUDs: The Basics
An IUD is a T-shaped plastic device that your doctor inserts in your uterus. To prevent pregnancy, Mirena slowly releases levonorgestrel to:
- Thicken the mucus in your cervix, so sperm can’t reach an egg
- Thin the lining of your uterus
- Stop your eggs from fully developing each month
In addition to Mirena, several other IUDs release levonorgestrel:
- Skyla prevents pregnancy for up to 3 years.
- Kyleena prevents pregnancy for up to 5 years.
- Liletta prevents pregnancy for up to 6 years.
ParaGard is a different type of IUD. It contains no hormones. Instead, the device is wrapped in copper wire. This causes inflammation that is toxic to egg and sperm (but safe for you).
Mirena and Cancer Risk
Many studies have looked at the link between combination birth control pills (which have man-made forms of estrogen and progesterone) and the risk of breast cancer. Less research has been done on the breast cancer risks of progestin-only birth control, like the Mirena IUD.
Some research on progestin-only birth control suggests that it doesn't raise your chance of breast cancer. Here’s what one large study found:
- Breast cancer risk was slightly higher in the average population than in women ages 40-54 who used IUDs with levonorgestrel. That's the hormone in Mirena.
- Breast cancer risk was slightly lower in the average population than in women ages 30-39 who used these IUDs.
- Regardless of age, there was no major difference in breast cancer risk between women who used this type of IUD and those who didn't.
- How long women used the IUD did not seem to affect their breast cancer risk.
More Research Is Needed
If some studies suggest that progestin-only birth control doesn’t increase chances of breast cancer, why would Mirena carry a warning about breast cancer?
Research on progestin-only birth control isn’t strong enough to have a definite answer. The studies simply don’t have enough people.
Should You Avoid Mirena?
Based on what we know now, it’s probably a good idea for women with progestin-sensitive breast cancer to choose a different type of birth control. In this type of cancer, cancer cells have substances called receptors that attach to progestin. The progestin helps cancer cells grow.
You may also want to skip Mirena, and any other hormonal birth control, if you have a strong family history of breast cancer. It’s one small step you can take to help protect yourself.
There are more important steps you can take. These well-studied strategies have been shown time and again to reduce breast cancer risk:
- Reach and maintain a healthy weight
- Get regular exercise
- Limit or skip alcohol
Benefits of Mirena
When choosing birth control, discuss the pros and cons with your doctor. For you, the benefits may outweigh any possible risks. With Mirena, these benefits may include:
- Lighter periods after 3 or more months
- Less menstrual pain
- Less pain from endometriosis
- Lower risk of endometrial cancer
- Lower risk of pelvic infection
If you have a family history of breast cancer, be sure to tell your doctor.