What is an empty stomach?

DEAR DR. GOTT: I have two related medical questions that I have always wondered about. First, what does it mean, exactly, to take medication on an empty stomach?

I take prescription medication (Synthroid) daily due to hypothyroidism and it is to be taken on an empty stomach. How long must I have gone without eating before taking the medication to be considered to have an empty stomach? Also, how long must I wait after taking the medication before eating again? That is, if my stomach is empty when I take my pill, can I eat right away or must I still wait a period of time before eating so that I still have an empty stomach?
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