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 you are awake, your brain produces various waste chemical byproducts as part of its metabolism while performing the various functions needed to keep you aware, alert, and active. The longer you stay awake, the more of these waste products it produces, until they begin to interfere with the functioning of the brain. The mechanism the brain has to remove these waste products cannot operate while the brain is awake. Caffeine and other things can give a temporary rush that can help the brain work around the waste products to continue working, but eventually the waste products build up too far.
Caffeine basically blocks the receptors that tell you that you need to sleep
When you actually sleep, a lot of things happen including your brain being washed. Fluid comes in and washes the old fluid out. This is a very simple explanation and it’s far more detailed
Your muscles also relax and helps in repairing them
This is something caffeine cannot reproduce
Your brain needs to rest and recover for a set period of time. We do this by falling asleep. Getting tired is just your body telling you it’s time to get some rest and go to sleep.
Caffeine is a stimulant, which means that it tricks you into thinking you are not tired. Basically “covering up” the tired feeling. What it does not do is actually refresh your brain and body in the same way sleep does.
So after a certain number of hours, when the caffeine stimulation wears off, you will feel tired again – likely more tired than before you consumed caffeine, because you “covered up” a few gradients of feeling tired, but did not stop the process of actually getting tired. Of course, you can just consume caffeine again.
But eventually, one of two things will happen:
* You will be so tired that even caffeine can’t cover it up enough, and you will crash, OR
* If you power through enough, your body will eventually give away in more dangerous ways (such as a heart attack) because you aren’t giving it the rest it has been needing to recover. Reaching this stage is relatively difficult as most of us just crash before getting to this.
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Think of it like a bad charger cable. You can put some tape around it, and it will hold enough to work again. The tape allows the cable to continue functioning, but it does **not** fix the cable. Eventually, the tape will wear away and the cable will deteriorate some more. You can always wrap it in tape again, but eventually, the cable will just rip completely no matter the amount of tape.
Caffeine doesn’t make you not *need* sleep, it just makes you *feel* like you don’t need sleep. As you go through the day, your brain builds more and more *adenosine* which signals your body to feel fatigued. When you sleep, your body cleans up all that adenosine, so that in the morning you aren’t fatigued. The adenosine is really signaling to your brain and body that there’s a lot more going on – your brain needs to perform clean-up for a lot of different neurotransmitters and waste products.
The exact reason for why we need sleep is not well known. Probably we need to do that clean-up. Why can’t we do that while we’re awake? Scientists don’t know for sure. It probably interferes with your ability to form conscious, coherent thoughts. Sleep is also important for learning and building memories. Again, the exact mechanism isn’t known but during sleep your brain seems to build new connections better. So, what the adenosine is doing is telling your brain that it’s time for all that, *especially* the clean-up part.
Caffeine binds to the same receptors that the adenosine binds to, but caffeine doesn’t activate them. Instead, the caffeine just gets in the way and prevents the adenosine from working. It’s like the adenosine is a key and when it turns the “lock” in certain neurons, those neurons fire off “we’re tired” signals throughout your brain and body. The caffeine is like jamming the wrong key into that lock, so that it can’t unlock and the right adenosine “key” doesn’t fit in there anymore.
That works temporarily, but as your brain gets more and more “dirty” with waste products, and you keep putting off that clean-up cycle, the adenosine builds up more and more. You don’t build a “tolerance” for caffeine, so much as your tiredness just overwhelms the caffeine and you feel tired anyway. Eventually, your brain really just starts shutting down to preserve itself and do the clean-up tasks that it *must* do in order to function, regardless of how much caffeine you have.
Plus, caffeine stimulates the production of adrenaline, which is a hormone that signals your body to be alert and awake. For example, when you get scared, your brain dumps a ton of adrenaline to really ramp you up and get you ready to fight or run for your life. Your brain is always adding *some* adrenaline, though, to control how your body is functioning. Caffeine makes your brain increase the adrenaline that it produces, which gives you a bit more pep.
However, one organ significantly affected by adrenaline is your heart. Adrenaline makes your heart beat faster, spreading vital oxygen throughout your body when you might *really* need a lot (in order to fight or run). Your heart can’t keep that up forever, though. It never stops beating (until you die) but it *does* need to slow down and rest, just like your brain. Too much caffeine will cause an irregular heartbeat and can lead to palpitations (when you can feel your heart thumping in your chest). Normal caffeine consumption doesn’t really hurt you, but if you’re ingesting enough to keep you awake when it’s really unhealthy and you need to be sleeping – combined with your brain not really working the way it should be, the adrenaline can really mess with your heart start damaging your heart and fatigue your heart until it stops working correctly. Which is, you know, bad.
Point being, at some point your brain *must* sleep in order to function, and your heart *must* slow down and rest. Caffeine prevents those things from happening, which is ok when it’s in moderation, but pretty terrible if you try to postpone the inevitable.
Maybe a better question to ask yourself is why you need to sleep at all. If you can get so much done, be so productive, make food, make objects, keep watch… why would you evolve to shut down for a third of every day?
That’s an awful lot of shutting down and not being productive, and pretty frequently.
Well, the answer to that is, not sleeping makes your brain not function very well.
Your brain working isn’t a zero-sum game with the chemicals it uses. Instead it makes and consumes them more like gasoline, polluting its area, and its clean-up cycle happens during a lower function mode (sleep).
If that doesn’t happen, eventually it will die or put you into some very dangerous situations through delusion/hallucination.
And besides that, caffeine is more like a suggestion than an ‘on’ switch. Especially as you get adjusted to it. If you are tired and sleepy, it takes a lot of caffeine or even a more powerful stimulant to stay awake through sleepiness, until maybe you get to the point where your hormones stop doing their jobs so well and you stop getting those signals and stop being in control of being awake.
Actual ELI5: Caffeine doesn’t keep you awake, it just stops you feeling tired. That might help you stay awake longer, or make it harder to settle to sleep if you had a coffee before bed, but eventually you’re going to drop off.
I don’t understand this well enough to explain, but I do understand it enough to be excited to read the explanation and all the responses!
Caffine blocks the chemical signal that makes you feel sleepy. This also can make it more difficult to purposefully falling asleep. It doesnt stop your body from saying “Hey! Ive had enough from you tonight, young man, you get your ass to bed right now. “
Lets say you have a car. You see the gas is low, so you fill it up. That is sleeping.
Lets say you have a car. You see the gas is low, so you block the dial. That is taking caffeine.
One allows you to continue, while one helps you ignore the problem
The WIRED “support” episode about sleep covers this. Take a peak if you want.
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