How does birth control pills help you regulate you period? and how long should you take them if thats the only purpose of taking them?

BC Pills: Bc pills work by giving you a constant concentration of hormones (an estrogen & a progesterone). Usually, fluctuations in your body's hormones control your cycle and ovulation. Bc pills give a constant amount of the hormone; during the 'off' days you're taking a sugar pill (no hormones); the drop in hormones causes your period. Take the pills as long as you want to regulate your cycle.

Programmed cycle: Birth control pills use hormones to supress ovulation. Those same hormones effect the lining of the uterus so when you take the pills without hormones you have your period. It is overriding whatever cycle you normally have - regular or irregular. They do not fix the problem you have that is making you irregular. You can take them up to age 35 for smokers and into the 40's for non-smokers.