Could taking birth control pills and substituting sugar pills with real ones all month round be harmful?
It would be pointless. The sugar pills do not contain anything
in them to keep you from getting pregnant. The placebos (or sugar
pills) are there as "reminders" to keep you in the habit of taking
them and so when you know to start a new pack. The sugar pills are
not needed during your period,that's why they are sugar pills. If
you take the placebos when you are supposed to be taking the
"active" ones, they are inaffective and you might as well not be
taking them at all.