Levonorgestrel
"I was sure I was ovulating when the condom broke, but I took Plan B 9 hours after the incident. I read on the Planned Parenthood website that if you are ovulating or have already ovulated, Plan B has no effect in preventing pregnancy. Luckily, I got my period on the exact day that I was supposed to. I rated 10 stars because if taken before ovulation, it is very effective as it mainly works by delaying ovulation. However, during or after ovulation it's not clear that it works to prevent pregnancy. I didn't get pregnant, and it may be because Plan B did it's job in preventing implantation, or it could have been because I was not actually ovulating. It is difficult to tell when exactly you are ovulating. Don't freak out just yet. Good luck!"