As long as fiber is combined with plenty of extra water, with five or six glasses daily being fine, the bowels WILL move under normal
constipation circumstances,
and under medicine-induced
constipation, as long as some way of making the bowels move is used, then fiber is not the enemy.
Actually, pain-killers don't ONLY slow bowel movement, but primarily they are drying in their effect, hence the sensation of "dry mouth." This is why water is so important.