caffeine suppresses receptors for the alarm molecules that accumulate as you remain awake, called adenosine. unable to detect the adenosine levels, you are unable to feel tired. however if you’re already tired, those receptors have already been triggered, so coffee is actually kind of bad for waking you up from being sleepy. it will stop any further sleepiness, if you fight off what sleepiness you have. (at least until the brain responds to strangely low detected adenosine by growing more receptors, and now caffeine doesn’t block them all unless you drink even more coffee)

And the coffee tips Celestia off, and she raises royal hell when she finds out how they’ve been treating Spike.

@Officer Hot-Pants
 
Damn, and that sounds pretty hilarious too.

@raw19  
I recall reading a story a while back where someone did take advantage of that, though only for pranks. Don’t remember exactly what they sent her.

@neo4812  
Very good thing.

@raw19  
good thing they haven’t discovered how to make bombs yet

@brony-in-denial
 
That would be truly hilarious.
 
…..Huh. In a way, Spike is a serious weakness of Celestia’s. If someone kidnapped Twilight or Rarity, they could force Spike to air-mail bombs to Celestia’s face.

Spike, you know it’s against the law for dragons to drink coffee.

spike language!

Run Spike ! D:

And now Celestia’s covered in hot coffee.

oh boy more patronizing

Who goes there!?