Oda doesnt drop this info for nothing: So I am afraid to think about what will happen after though. The medicine did heal him, but didnt restore his energy.
Anyway, Oda didnt draw a full sequence to show that the medicine kick off, that tell me that Zoro is just resting due to Enma draining his energy. Why is Oda holding the effect of the medicine especially after Zoro finishing his fight with King. Simple more is coming.
How do we know that the medicine will kick in? well Oda will draw that which didnt happen yet.