An intrauterine device (IUD) is a small, T-shaped contraceptive device that a healthcare provider places inside a woman's uterus to prevent pregnancy. IUDs can be made of plastic or copper and work by either releasing hormones or creating an environment that is toxic to sperm. They are highly effective and can last several years, depending on the type. IUDs are considered a long-acting reversible contraceptive method. They can be removed at any time by a healthcare professional, allowing for the possibility of pregnancy to resume quickly. IUDs do not protect against sexually transmitted infections (STIs), so additional protection may be necessary.