How ineffective is BC when taking antibiotics for an infection? I just got prescribed antibiotics for what is thought to be a throat infection and the pharmacist told me my birth control will be ineffective...I assume in the sense of safe sex but like is it ineffective on regulating and such? My periods are heavy (8 days mostly a super plus tampon time for like 6 of those days) I need all the help I can get in lowering the heaviness and the inconsistencies in my cycle