Evra Patch 3'sThe Evra patch is a hormonal birth control method that releases synthetic estrogen and progestin directly through the skin to prevent pregnancy. It works by stopping ovulation, thickening cervical mucus to block sperm, and thinning the uterine lining. When used correctly, it is up to 99% effective. How to Use It Application Schedule: Apply one patch a week for 3 weeks in a row to clean, dry skin on your buttocks, abdomen, upper outer arm, or back.