Levonorgestrel
"My boyfriend and I had an accident where the condom slipped last week on Wednesday, May 15. Within the first hour, we went to a pharmacy and I took Plan B One Step. I was nervous because my period didn't come on Saturday, like it was supposed to. Keep in mind that I also recently went off of birth control so I could switch brands, so my period would have been erratic anyway. Still, as you can imagine, I lived the next days in panic. But the package on the box says to wait up to one week after your expected period. It has been nine days since I've taken the pill, but sure enough, this morning, Friday, May 24, I woke up with terrible cramps and lots of bleeding. I've never been so happy to get my period!"