It all depends upon your blood test results. If your numbers are in the normal range ie (what a 23 y.o. Chinese flighter pilot has) then you should be ok. I wouldn't bring it up during the medical. If everything tests normal even though you use medication you should be fine. If your numbers are outside of the normal range they will order extensive blood/thyroid tests and I doubt you have any chance. In other words don't let the cat out of the bag until it is discovered.