A thin, beign square patch (1.75 inch square) that a woman wears on the skin of her belly, upper arm, butt, or back. It contains estrogen and progestin. It works by preventing ovulation, by causing the cervical mucous to thicken to prevent sperm from entering, and it makes the endometrium thinner to help prevent implantation. The advantages can include more regular periods, decreased period flow, less cramping, less acne, and a decreased risk of ovarian, uterine, and colorectal cancers. The disadvantages can include having a lower sex drive, mood issues, headaches, breast tenderness, and it is less effective in women who are obese. The failure rate is 7% per year with typical use.