system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do so many brands of energy drinks, and sometimes even coffee, just put me to sleep right away?  I don’t think I have ADD or anything else that could cause reverse reactions.

* Red Bull makes me zonk the eff out asap

* 5 Hour Energy Drink used to work, but now only the maximum 5 HR Energy works *sometimes*

* Monster *may* work, *sometimes*.  

* Rockstar and Redline usually work.
gpt
If you're already tired, caffeine won't work too well. Since you're five, I'll just put it this way.

In your brain, there's something called adenosine. You know those shaped blocks with squares, circles, diamonds and stars? Your brain has ZILLIONS of little holes shaped like that, and adenosine is like a block that's shaped like a star. So it fits in the little star-shaped holes. Inside those star-shaped holes are buttons that tell your brain that you're sleepy. (There's a lot of other kinds of buttons too.)

When you drink things like coffee or Red Bull, they have caffeine. Caffeine is also like little star-shaped blocks, but they're uhh... really fluffy. So they don't push the sleepy buttons in your brain. So you don't get tired. However, if there's already a bunch of adenosine blocks ALREADY pushing your sleepy buttons, they're taking up all the star-holes in your brain and the caffeine is too late. If the caffeine gets there first, then they won the race and block the buttons in the star-holes, so you don't get tired at all. 

But then you can't go to sleep and you drive your mom and dad crazy.

On the other hand, if you're not tired at all and caffeine makes you go to sleep, maybe you have really sensitive sleepy-buttons.