Levonorgestrel
"I have taken Plan B 3 times so far and has worked every time. First time in July 2012 I had unprotected sex took Plan B 4 hours later and got my period with no delay on the exact day I was supposed to get it. The second time in September 2013 I just finished having my period on 8/20 and had protected sex on 9/4, the condom broke so I took Plan B 2 hrs later and got my period 2 weeks early on 9/9. The third time I took it was March 2014. Had a condom break so I took Plan B on 3/21, 4 hrs later. I was suppose to get my period on 4/2/14 but got it yesterday it came 3 days early. Never been so happy to see my period. If you are worried that the pill may not work don't be! It does work when you take it writhing the 72 hour time frame."