The other day, in a conversation about the meme of "X is natural, so it's good for you!", I jokingly suggested strychnine arsenate. Strychnine is an alkaloid, so can form a compound with acids, for example arsenic acid (H₃AsO₄, analogous to phosphoric acid).
I am slightly surprised to discover that not only is it a thing, not merely is it a compound with
known properties, there are chemical suppliers that will
sell it to one.
The only use for it that I've been able to find in a quick on-line search, apart from a cagey "chemical research", is for making homeopathic preparations. I might have guessed.
It's possible that its real purpose in supply catalogues is to send a warning note to local police agencies that they might want to keep an eye on you.