Levonorgestrel
"I had a mishap with my boyfriend on Sept.4 where he came inside of me and immediately ran to CVS to get the Plan B. I took the pill within an hour of the accident.  I'm not sure whether it was a mixture of the Plan B and my regular birth control (which I started Sept.5) but the side effects hit me hard. I was extremely naseuas and fatigued. I mean to the point where any physical activity was draining. This went on for the next two weeks with mild cramping in between. The side effects subsided a bit but I am happy to say that my period came today Sept.29 only a day late! I am well over the "weight limit" for the pill and it worked for me and I was very fertile according to my ovulation calend. Hope this helps someone ease their minds a bit!"