Mirena is considered safe for most people. It has been FDA-approved since 2000, carries no boxed warning (the FDA’s most serious safety label), and is one of the most studied contraceptive devices in the world. That said, it does carry real risks that vary depending on your health history, whether you’ve recently given birth, and whether you’re breastfeeding. Here’s what those risks actually look like.
How Common Are Serious Complications?
The complications that concern people most are uterine perforation (the device poking through the uterine wall) and pelvic inflammatory disease (PID). Both are rare, but worth understanding.
A large multisite study found that the overall five-year rate of uterine perforation was 0.61%, or roughly 6 in 1,000 insertions. For people who were not recently postpartum, that rate dropped to 0.29%. For those who had recently given birth, the rate was higher at 1.37%. Breastfeeding further increases the risk. Perforation can reduce contraceptive effectiveness and sometimes requires surgical removal, but it’s not common.
PID risk is highest in the first 20 days after insertion, according to the CDC. After that initial window, the rate drops significantly and stays low for the life of the device. People who have an existing sexually transmitted infection at the time of placement face a higher risk, which is why screening typically happens before or on the same day as insertion. Same-day STI screening and placement has been shown to keep PID rates low.
Expulsion: When the Device Comes Out on Its Own
About 1 in 20 Mirena users will experience expulsion, where the device partially or fully slips out of place. This is most likely in the first three months, and especially within the first year. Expulsion can happen without you noticing, which means contraceptive protection drops without any obvious sign.
Several factors raise the odds. Insertion right after vaginal delivery carries a 17% expulsion rate at six months, compared to about 3% when placement happens later. Expulsion rates are also higher after cesarean delivery (though less so than after vaginal birth), in adolescents, in people with fibroids or uterine cavity distortion, in those with a BMI over 25, and in people who use menstrual cups alongside the IUD. If you’ve had a previous expulsion, you’re more likely to have another one.
Pregnancy With Mirena in Place
Mirena is over 99% effective at preventing pregnancy, but no method is perfect. If pregnancy does occur with the device still in place, the risks are serious: ectopic pregnancy (where the embryo implants outside the uterus), miscarriage, infection, and preterm delivery. The FDA labeling states that Mirena should be removed if pregnancy is detected, though removal itself carries some risk of pregnancy loss.
Breast Cancer: A Small but Real Signal
This is one of the more debated aspects of Mirena’s safety profile. A large study reviewed by the American College of Obstetricians and Gynecologists found that Mirena users had a relative risk of breast cancer of 1.21 compared to people who had never used hormonal contraception. In practical terms, that’s a 21% increase in relative risk. Notably, this risk did not grow with longer use, which is unusual for a hormone-driven effect.
To put this in context, the absolute increase in risk is small because breast cancer rates in premenopausal people are low to begin with. A 21% relative increase on a small baseline number is still a small number. But for anyone with a personal or family history of breast cancer, it’s a conversation worth having before choosing Mirena. The device is not recommended for people who currently have or have had breast cancer.
Mood Changes and Depression
Mirena releases a low dose of a progestin hormone directly into the uterus, and most of it stays local. But some is absorbed into the bloodstream, and for certain people, that’s enough to affect mood. Hormonal contraceptives of all types, including Mirena, can influence emotional well-being, particularly in people who already have depression or a family history of it.
There’s no reliable way to predict whether Mirena will affect your mood before you try it. For people without a history of depression, negative emotional effects that do appear tend to resolve within a few months. For those who are already managing a mood disorder, the picture is less predictable, and the effects may persist.
Ovarian Cysts and Bleeding Changes
Mirena can cause enlarged ovarian follicles or cysts. These are usually painless and resolve on their own, but they occasionally cause pelvic discomfort and may need monitoring. Your provider will want to evaluate any persistent cyst.
Bleeding changes are one of the most common experiences with Mirena, not dangerous but worth knowing about. Many people have irregular spotting for the first three to six months. After that, periods often become much lighter, and some people stop having periods entirely. This is a normal hormonal effect, not a sign of a problem, but it catches some users off guard.
Who Should Not Use Mirena
Mirena is not appropriate for everyone. You should avoid it if you have:
- Breast cancer (current or past)
- Uterine or cervical cancer
- Liver disease
- An active pelvic infection or current pelvic inflammatory disease
- Unexplained vaginal bleeding
- Uterine abnormalities, such as fibroids that interfere with placement or a uterus that isn’t typically shaped
If you’re postpartum, timing matters. Insertion right after vaginal delivery raises the chance of expulsion. And if you’re breastfeeding, the risk of uterine perforation during insertion is higher than it would be otherwise.
How Long Mirena Lasts
Mirena is currently FDA-approved for up to eight years of contraceptive use, following a label update in 2022 that extended it from the original five-year approval. The device continues to release enough hormone to prevent pregnancy throughout that period, and there is no evidence that safety risks increase with the extended timeline. After eight years, or sooner if you choose, the device is removed in a quick office procedure and fertility typically returns rapidly.