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How Does Mirena Work to Prevent Pregnancy?

There is no single explanation for how Mirena works; most likely it prevents pregnancy in several ways.

Mirena releases small amounts of a progestin-only hormone (levonorgestrel) locally into your uterus. This is the same hormone that is often used in birth control pills.

Mirena may:

• Thicken cervical mucus to prevent sperm from entering your uterus
• Inhibit sperm from reaching or fertilizing your egg
• Thin the lining of your uterus

Mirena may stop the release of your egg from your ovary, but this is not the way it works in most cases. Most likely, the above actions work together to prevent pregnancy. Like other forms of birth control, Mirena is not 100% effective.

Indications & Usage

Mirena (levonorgestrel-releasing intrauterine system) is a hormone-releasing system placed in your uterus to prevent pregnancy for as long as you want for up to 5 years. Mirena also treats heavy periods in women who choose intrauterine contraception.

Important Safety Information About Mirena

Only you and your healthcare provider can decide if Mirena is right for you. Mirena is recommended for women who have had a child.

• Don't use Mirena if you have a pelvic infection, get infections easily or have certain cancers. Less than 1% of users get a serious infection called pelvic inflammatory disease. If you have persistent pelvic or abdominal pain, see your healthcare provider.
• Mirena may attach to or go through the wall of the uterus and cause other problems. If Mirena comes out, use back-up birth control and call your healthcare provider.
• Although uncommon, pregnancy while using Mirena can be life threatening and may result in loss of pregnancy or fertility.
• Ovarian cysts may occur but usually disappear.
• Bleeding and spotting may increase in the first few months and continue to be irregular. Periods over time may become shorter, lighter or even stop.