Eli5 why can’t we continuously take caffeine and never sleep?

Question

I work overnight shifts (11pm-7am) and take caffeine pills to stay awake. When I get home, even if I take more caffeine I’m sometimes still too tired and fall asleep. Why does it eventually stop working? Is there some sort of chemical limit? Why can’t caffeine replace sleep for longer periods of time (like days on end)?

In: 595

Answer 1

Actual ELI5:

When you go through your brain produces sleepy chemicals. When you have caffeine, it allows you to ignore those sleepy chemicals by turning off the things that detect them in your brain. But that doesn’t stop your brain producing the sleepy chemicals, just stops you from noticing them for a bit.