What is the effectiveness of Mirena?

Mirena is over 99 percent effective for birth control, according to the Mirena website. Once a health care professional places the intrauterine device, it continuously prevents pregnancy for up to five years.

Mirena offers low-maintenance birth control. A patient needs to check once a month to ensure it remains correctly positioned, notes Mirena. The intrauterine device releases a hormone that prevents pregnancy and reduces heavy bleeding during monthly periods. When a woman wants to become pregnant, her health care professional is able to remove the device. Approximately 80 percent of women become pregnant within one year once the device is removed.