An IUD, or intrauterine device, is a small, T-shaped device that a healthcare provider places inside a woman's uterus to prevent pregnancy. It works by either releasing hormones or using copper to create an environment that is not suitable for sperm, thus preventing fertilization. IUDs can be effective for several years, depending on the type. There are two main types of IUDs: hormonal and copper. The hormonal IUD releases progestin, which thickens cervical mucus and thins the uterine lining, while the copper IUD uses copper to deter sperm. Both options are reversible, meaning fertility returns quickly after removal.