IUD hormonal or copper, hormonal IUDs use the hormone progestin which thicken the mucus that lives on the cervix, which blocks and traps the sperm, and 2) the hormones also sometimes stop eggs from leaving your ovaries, copper is toxic to sperm. It makes the uterus and fallopian tubes produce fluid that kills sperm, side effects include pain during insertion, irregular periods, heavy periods with stronger cramps