The Amicale only cares for fairies' health as far as it's required for a good Dust harvest. If a fairy's health costs more than it yields, they'll want to kill it.
That drug is a fairy hibernation hormone, it would have no effect on other creatures. In cities, fairies more commonly use antagonists, not to spend half of their life sleeping for nothing, but it still has its uses, like if a fairy has a health condition that requires extended rest.
Myces responds to the hormone, but is looks like her gland is not growing as fast as the rest of her.
You put some pretty deep thought into your story, its quite impressive!
It's the most amusing part for me!