throughout the body, but we have the body actually producing that drug. So we have at least two sources or more sources for that substance to appear in blood.
And to make things even more complicated, especially with hormones, there's also a feedback process where it isn't simply a steady body production, that as blood concentrations go up and down, that production and that storage of that compound changes with changes in the blood concentrations or the body concentrations. So that adds a level of complexity that really creates certainly technical problems in using our normal methods for doing bioequivalence, and certainly that process and the amount in blood that did not come from our formulation has to be taken into account if one hopes to use pharmacokinetic measures to determine bioequivalence and determine difference between formulations.
So I've redrawn this and it's drawn for illustration, not entirely supposed to be accurate or representative of any given product, but I've changed the supposedly nice properties of pharmacokinetic data to say, well, now we're dealing with a baseline or that substance is already there before we start to add the contribution