Evra Transdermal Patch is a patch type birth control which is indeed designed to prevent pregnancy by delivering two types of sex hormones. Ethinylestradiol is a synthetic estrogen, which is commonly used in various hormonal contraceptives. Estrogen plays a role in regulating the menstrual cycle and suppressing the release of luteinizing hormone (LH). Norelgestromin is a synthetic progestin, which is a synthetic form of the hormone progesterone. Progestins are known to have various effects, including thickening of cervical mucus and alterations to the endometrial lining. The combined actions of ethinylestradiol and norelgestromin in the Evra patch help to prevent pregnancy through multiple mechanisms. The primary mechanism of action is the suppression of ovulation, which means that it prevents the release of an egg from the ovaries. The patch also alters the cervical mucus, making it thicker and less permeable to sperm. This makes it more difficult for sperm to penetrate the cervix and reach the egg. Changes in the endometrial lining may reduce the likelihood of implantation of a fertilized egg in the uterus. The combination of these mechanisms makes Evra an effective method of contraception when used correctly.