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)?
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Imagine that fatigue is the force that gradually, harder and harder, presses on the sleep lever.
Caffeine temporarily blocks the switch (adenosine receptors) and creates an opposite force (cortisol, dopamine) making sleep impossible. But the force that acts on the switch continues to increase as if nothing is happening.
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