As a medical doctor, i get very frustrated reading some very wrong information. Birth control pills are 99% effective. The reason they are not 100% effective is because there is always a chance of a patient missing a dose or taking a dose very late and effect the hormone cycle in the body. Some older brands of birth control did require you to take them for at least 14 days before having unprotected intercourse; however, many of the new brands available right now, it only requires 7 days. Some doctors do suggest their patients to be on the pill for at least couple of weeks before having unprotected sex, but that is just to be on the safe side. After the required period, if you do not miss your dose and take the pill correctly, your are protected from pregnancy! I have read some stupid comments in here and let me clear something up:
whoever says that you can get pregnant while taking birth control correctly has either no idea how the female cycle works or what birth control pills are. Its always best to consult with your own family doctor to make sure the pill that you are on only requires 7days. There are no pills on the market that require you to take them for 3 months to be protected.