Levonorgestrel
"I had an accident on the most fertile day of my cycle and was so afraid since both of my children were conceived on the first try so I am incredibly fertile. I took the pill an hour after sex and had minimal side effects over the next week. Mostly menstrual like cramps and tingly breasts. However because those can be pregnancy symptoms I was totally panicking. 9 days after taking the pill I had some strong cramps and noticed a little bright red blood after wiping. I thought it was implantation bleeding since my period wasn't due for another 5 days and I had it with both my other pregnancies. I figured the pill didn't work since I took it on the day of ovulation. But over the next hour it turned into a full period! Plan b worked!!!!!!!"