So something that I've been a little confused about - plan b(morning after pill) is about 90% and above effective if you use it within the first 24 hours, then decreases effectiveness and is pretty much useless after 5 days after unprotected sex. I've been told that plan b is just a much higher dose of hormones than birth control. So why is it that regular birth control is so much more effective than plan b if the dosage is lower?