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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When the fuel light comes on in your car because you’re low on gas, you can make the light turn off temporarily by driving up and down hills and tricking the gauge, but that doesn’t actually put more gas in your car—when it runs out, the car will stop running, even if you somehow tricked the fuel light into turning off (or even broke it). It’s kinda like that. Your body needs sleep to run either way—feeling tired is just the warning light. Caffeine doesn’t replace sleep in the same way that breaking a signal light doesn’t solve the root problem that it turned on to alert you of.
This isn’t really an answer to your question, but just some examples of what happens to a body when extremely sleep deprived. When I was in architecture school, people would often live off maybe 8 hours of sleep. For the whole week. And then pull two all-nighters in a row. And that was usually preceded by weeks of significant sleep deprivation as well. By the end of it, we would look and feel so disgusting. Our skin would be mottled. Our faces would look like they had been deflated. People would sometimes randomly vomit. We’d have gastrointestinal problems, body tremors, heart palpitations. My body would have a hard time regulating my body temperature. We had to make models during this time and many would have accidents, like pushing their fingers into bandsaws and sanding their whole fingernails off with belt sanders. It was a truly horrible culture. If you’re motivated enough, you can stay up for long periods of time, even to the point where you’re breaking your body down. I somehow did it without caffeine, but most of my classmates drank it. I know you’re just asking out of curiosity, but our bodies need sleep to function properly. If they don’t get it for prolonged periods, everything starts to go downhill. No one is missing out on any extra life by getting good sleep. Good sleep makes all your waking hours better.
Because without sleep, you will eventually hallucinate and then die, and your body knows this and will try to shut you down before you get there.
Caffeine doesn’t replace sleep or make you feel rested, it stops you feeling tired despite being so
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.
The way that I’ve always understood it is that caffeine takes up receptors in your brain that are intended for your natural sleep chemical.
But the sleep chemical builds up in your brain like a pressure and eventually the pressure will get so high that any more caffeine added to the mix simply won’t be able to reach those receptors before the sleep chemical can and your brain will fall asleep
I’m sure other people can add greater detail, or more information but I thought I’d keep it simple (plus I’m not an expert so that’s about the extent of my understanding anyway :P)
Caffeine fits into the pockets where adenosine is supposed to go. When the adenosine fills up the pockets, it makes you sleepy. When the caffeine is in the pockets, the adenosine can’t fit. Your body is all like “I made adenosine, but still no sleepy, I guess I’ll make extra tomorrow because if no sleepy, then dead.” Body then makes too much adenosine and the pockets get full too early. Don’t fill your adenosine pockets with caffeine. Get some sleeytime.
Body becomes resistant to caffeine levels if you continuously take it your body operates normally as if you had never had any.
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.
Ever been around someone with mania who’s been up for 3 days? That’s why.
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