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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Your body is very good at building tolerance to caffeine because sleep is important for survival so it will adjust itself to become more tolerant to higher doses as you ingest more and more coffee. Caffeine blocks adenosine from signalling that you’re tired so you feel awake but your body responds by building more adenosine receptors to counter this chemical from stimulating you.
Adenosine never leaves your body, it just builds up more and more while the receptor is blocked. Eventually your body will be so overloaded with this that it will collapse asleep the moment your half-life on caffeine hits or your tolerance builds up high enough.
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