I read this short story a long time ago (maybe early 2000's?) and I feel like I maybe have invented many of the details, but here's what I remember:
I think it was a magical realist author, like Borges or Márquez or something. It was probably in a collection of short stories. I was reading a lot of 60's and 70's sci-fi at the time, so it might have been a collection of that sort of story. The setting was Earth or earth-like, with a vaguely fantasy/historical feeling. The story took place in a village, I think, with a marketplace.
The story was about a man who wants to commit suicide, but he has obligations he feels bad about walking out on. Instead, he buys a potion which will induce unconsciousness - his body will still perform all the actions as if he were alive, but he will have no subjective consciousness of it. Basically a philosophical zombie.
Meanwhile, another character wants to murder the guy (for some reason?) but feels bad about it, so he buys the same potion and slips it to the guy.
The climax of the story is that the original character, having been fed the potion in his sleep, wakes up, seems to debate with himself, and then takes his own dose of the potion.
I guess it's a story about the nature of consciousness etc? I feel like the story was maybe named for the potion seller, like the market where he bought the potion, or something? The trouble is that I'm not sure how much of the above actually happened in the story, and how much I've constructed trying to make it make sense when I told someone else about it.