As I understand it, substances will have different effects depending on how they are applied. So, a substance that might have a medicinal use if applied topically could be a toxic poison if ingested.

And I am sure the devs, looking over your question of which skills would be involved, would say, "yes." That is, all those skills would be involved -- possibly in combination, possibly sequentially. So, an apothecary might need an ingredient prepared by a skilled alchemist who used ingredients from a skilled herbalist.

I imagine that people will go around the world asking "delectable tea or deadly poison?" And sometimes the answer, like the answer to the skills, will be "yes."

Beathan's correct. There will be different ways to apply poisons and the effects will vary based on how they are applied. What we don't have is any definitive guide or list of toxins in the game. And chances are that SBS won't give us that. As with everything, this will likely be left to players to discover and document.

There also won't be any sort of modeling of the metabolics of poisons (or medicines) so nobody has to worry about how a poison will take effect. It's beyond the scope of this game (and really any game) to model the chemical reactions and processes that take place within the body.