The Mirena is a type of IUD, that is placed inside your uterus (by a doctor or nurse practitioner) to prevent pregnancy for up to 5 years. It's a T-shaped piece of plastic that emits hormones into your uterus directly, so it is considered an IUC (intrauterine contraceptive) or an IUS (intrauterine system). The hormones stay in the uterus and are not systemic, meaning they do not go to other parts of your body. This is why it won't cause significant weight gain like oral contraceptives sometimes do or increase breast tenderness. Another bonus is that the Mirena might also shorten, lighten, or even eliminate periods while you use it.
OK, but how does Mirena work? The small amounts of levonorgestrel (hormones) released by Mirena make your cervical mucus thick and tacky so sperm can't swim through it so it is difficult for them to make it to your uterus. If the sperm get in, then they can't make it to the egg to fertilize it.
Another way the Mirena, or IUDs in general, prevent pregnancy is it promote the production of white blood cells. When a foreign object is placed inside the uterus, the body creates white blood cells to defend itself. So when you have sex, if sperm do make it through your tacky mucus to your uterus, the white blood cells will attack them. Even if a sperm does fertilize the egg, the white blood cells will destroy that too.
Interested in how effective it is? To see the stats, just read more
Mirena is 99.9% effective at preventing pregnancy and like metal IUDs, it needs to be fitted and removed by a medical professional. Though once it's in place, that's it. You won't need to use any other form of birth control or even think about it.
Fit's Tips: Mirena is great if you are looking for hassle-free birth control for up to 5 years straight. Just a reminder, it DOES NOT prevent against STDs, so that's why it's great to use if you are in a long-term relationship with someone you know is disease-free.
It's also a great option if you've already had kids and aren't planning on having anymore, or if you know it's going to be many years before you want to start a family. If this interests you, ask you doctor about Mirena. Some doctors recommend against the using the IUD if you have not had children for they are more difficult to insert if you haven't had children.