Mirena is a hormonal intrauterine device (IUD) that's inserted into the uterus for long-term birth control (contraception). A T-shaped plastic frame that releases a type of progestin, Mirena thickens the cervical mucus to prevent sperm from reaching or fertilizing an egg. Mirena also thins the lining of the uterus and partially suppresses ovulation.
Mirena is one of two hormonal IUDs with Food and Drug Administration approval. The other is Skyla, which prevents pregnancy for up to three years. Mirena prevents pregnancy for up to five years after insertion.