Leatherworking: What are curing agents?

[skycaptain]

I've learned how to use Curing Agents, and it lets me add one when I craft an item. But what are they?! I can't craft them, I've searched google and I can't find the answer. What are the curing agents and how do I get them? Guides online tell me I unlock the ability to use them but they never tell me what they are.

[Elbob]

I believe those are made by alchemists, writhefire oil and stable fluidic draconium

[loras]

I've learned how to use Curing Agents, and it lets me add one when I craft an item. But what are they?! I can't craft them, I've searched google and I can't find the answer. What are the curing agents and how do I get them? Guides online tell me I unlock the ability to use them but they never tell me what they are.

Unironically piss, or something chemically similar. In real life anyway.
No idea what WoW uses though.