Normal birth control pills don't stop fertilization, so the 2 week old fertilized egg simply fails to send the signal that says, "Don't dump me" and the period happens.
Plan B does exactly the same thing, but not having the constant hormones in the blood means a bigger dose is needed for the effect.
In both cases, a fertilized egg--two week old baby if you prefer--is flushed down the toilet.
Normal birth control pills don't stop fertilization, so the 2 week old fertilized egg simply fails to send the signal that says, "Don't dump me" and the period happens.
Plan B does exactly the same thing, but not having the constant hormones in the blood means a bigger dose is needed for the effect.
In both cases, a fertilized egg--two week old baby if you prefer--is flushed down the toilet.