How long does Plan B take to start working?

It should take effect within 24 hours of taking it. However, it will not remove implantation if that has already happened. read more

Plan B will stop implantation from happening by causing you to begin a period that will remove the uterine lining in which the fertilized egg would have implanted, BUT if implantation has occurred, it will not work. read more

If you take it within 72 hours after you've had unprotected sex, levonorgestrel can reduce the risk of pregnancy by up to 89%. If you take Plan B One-Step within 24 hours, it is about 95% effective. read more

Update: Well, she took it about 40 hours after sex. I know plan b works by messing with her ovulation, but the thing is, she already ovulated. read more