Can you take birth control while on your period? will it last longer or shorter

Likely shorter: When first starting the birth control pill (bcp), you can start the pill as soon as you start your period and lilely have a shorter period. Most bcp's have 7 inactive pills to allow for a period - some of the newer bcp's have only 4 inactive pills. If you start your new pack of pills after only 3 or 4 days of the inactive pills in your pack, your periods will be shorter.