Plan B One-Step, Next Choice One Dose, and other levonorgestrel-based emergency contraception pills work because of the synthetic hormone progestin. Basically, progestin tricks your body into thinking it’s already pregnant. And that jumpstarts your body’s pregnancy-preventing reactions. Birth control pills use this same science (in low, daily doses). [On the other hand, ella acts to suppress progesterone](https://www.bedsider.org/features/850). This delays ovulation for up to five days, giving sperm time to die before an egg is released. (And that’s good because sperm can survive in your uterus anywhere from three to six days after sex.) Ella may also thin the lining of your uterus, making it harder for a fertilized egg to be implanted. While all [methods of emergency contraception] (https://www.bedsider.org/features/87) can be used up to five days after unprotected sex, Plan B One-Step and Next Choice One Dose are most effective when used within 72 hours (three days), and they work even better within 24 hours. But ella is just as effective on the fifth day as it is on the first.