The F.D.A. defines an empty stomach as “one hour before eating, or two hours after eating.” The F.D.A.'s two-hour rule is just a rule of thumb; the stomach will probably not be completely empty. The specific definition of an empty stomach varies from drug to drug.

What is the meaning of on an empty stomach?

Definition of on an empty stomach

: with nothing in the stomach : after having not eaten for a time Take this medication on an empty stomach.

Is it on an empty stomach or in an empty stomach?

without eating anything: You should never go to work on an empty stomach.