The Nature of the Device: The Mirena is an intrauterine device (IUD) developed and marketed by Bayer Pharmaceutics Company to prevent pregnancy for up to five years. The t-shaped plastic IUD is 99% effective, far better than oral contraceptives. Like other IUDs, the Mirena works by slowly releasing the birth-control hormone levonorgestrel into the uterus. The device is also approved to treat excessive menstrual bleeding.
