http://en.wikipedia.org/wiki/Emergency_contraception
The effectiveness of emergency contraception is presented
differently from the effectiveness of ongoing methods of birth
control: it is expressed as a percentage reduction in pregnancy
rate for a single use of EC. Different ECP regimens have different
effectiveness levels, and even for a single regimen different
studies may find varying rates of effectiveness.
he most common side effect reported by users of emergency
contraceptive pills was nausea
Other common side effects (each reported by less than 20% of
levonorgestrel-only users in both the 1998 and 2002 WHO trials)
were abdominal pain, fatigue, headache, dizziness, and breast
tenderness.[3][19][33] Side
effects usually do not occur for more than a few days after
treatment, and they generally resolve within 24 hours.[24]
