How long after taking the birth control pill does it become effective. i am taking the brand alesse if that matters.

Generally immediate: If the pill is started in the first 5-7 days from the onset of a menstrual period, it usually stops the next ovulation. To be on the safe side, use a backup method for 2 weeks. Remember, the pill does not prevent any diseases, so using condoms is generally recommended until marriage which will also serve as a back up method.