"ladies please note- bone of the ways plan b works is to prevent ovulation, so in simple terms, if you have already ovulated- it can be useless! that isn&#039;t something that was disclosed to me, &amp; most people have no idea! it&#039;s a catch 22 because you can usually only get pregnant when you ovulate ..anyways.. i had sex once, i took it 12 hrs after unprotected sex. ended up getting pregnant. i must have already ovulated.then i later had a miscarriage(chemical pregnancy) b/c the way my doctor explained it, plan b does three things: 
1. prevent ovulation
2. thicken cervical fluid (stops spermies)
3. thins lining of uterus to prevent egg implanting
i had a miscarriage b/c the egg was never able to implant. i feel horribly about it today &amp; wanted to share, hope this helps"