What would happen if I used regular eye drops while my contact lenses were in?
IANAD, but assuming you’re using soft contact lenses, the drug would probably be absorbed by the lens. This means that a) it’s not going where it’s intended to go; and b) if you don’t throw out your lenses after each wearing, the drug could build up in them to potentially dangerous levels. I don’t know how hard lenses would interact with drops, and this may not be true of all of drugs, but I know that I got strict instructions from several different doctors to make sure I removed my lenses before putting in my Patanol (allergy eye drops) and left them out for at least ten minutes after taking the drops.