How do emergency contraception pills actually work? Watch ASAP Science's short video below for a quick, informative tour of the female reproductive system and some interesting facts about conception (and prevention thereof). By altering the hormonal cycle of the female body, Plan B stops the egg from coming into contact with sperm altogether, either preventing ovulation or trapping sperm on the way. If the egg has already been fertilized, however, the pills have no effect. Mitchell Moffit and Gregory Brown, who produce the videos, talk about the making of the series in an interview with the Atlantic Video channel here.