So it is both food and poison at the same time. — Leghorn

Yep. Food poisoning is totally a thing (getting poisoned by your food), and this is the reverse of that (getting fed by your poison).

Therefore it both nourishes and poisons the body, and the body is both bettered and made worse at the same time. — Leghorn

No. It is intended by its user to poison the body, make it worse, but it has the effect of nourishing the body, bettering it. It's thus poison by its use-intent and food by its use-effect.

But I must make note of this apparent caveat in what you said: “TO THE EXTENT THAT the use of something”, etc.... — Leghorn

That caveat is because I'm not yet certain that this (new to me) idea of use defining a thing applies to all things. Do we use stars for something and is that what makes them stars, or are stars just stars because they are what they are? They don't seem to fit the pattern by which a rock can be made a chair not by any change to the rock, but by its being used as a thing to sit on.

Which also seems to connect to the gender example in the OP: a person is made their gender (but not their sex) by them being treated by society as a person of that gender. I guess maybe what all of this thread boils down to is that "chair" is a social construct; "food" and "poison" likewise? But not stars, or sexes?

They don't seem to fit the pattern by which a rock can be made a chair not by any change to the rock, but by its being used as a thing to sit on. — Pfhorrest

This reminded me of when I helped my landlord, Archie, one day repair a vacated room in the boarding house. He needed a hammer (we already had a nail), but neither of us had brought one. Spying an empty tequila bottle sitting on the window sill, Archie took it up and, wielding it like a hammer, drove the nail into the jamb. I was amazed that the bottle didn’t break during this process...but it didn’t. Indeed it admirably served as a hammer, without us having to go searching for a “real” one. I got the sense that Archie, being an old-timer, had not used this trick then for the first time...

...numerous examples of this sort of thing can be drawn from the teeth of necessity, the mother of invention. Who has not found a sheet of cardboard in the trunk of their car that could be cut and rounded into a funnel through which to pour transmission fluid or engine oil in lieu of an actual funnel made for that purpose?

The question is, did these extemporaneous things, cardboard and glass, in that moment, become hammers and funnels, or did they merely stand in for them as scrap packaging and containers of alcohol?