eli5 why does caffeine seem completely ineffective at times

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There are days where I can have a cup of tea or a can of redbull or even an espresso and just go to sleep in 15-20 minutes. But there are also days where it actually works. What causes this erratic behaviour of caffeine on the mind?

PS: I don’t intake a large amount of caffeine regularly but it’s behaviour is kinda weird

In: 25

From what I’ve read, it’s either just tolerance (though you say you don’t drink it regularly) or it could have to do with the amount of cortisol you have in your body.

Cortisol follows a rhythm and if you sleep and eat at regular times, production spikes when you’re waking up and when you normally eat lunch and dinner. Since cortisol inhibits the effects of caffeine you won’t really notice it if you’re drinking coffee around those times

Sources: random Internet articles

Edit: Soo, the more I’m reading about this the less confident I am in my answer so I wouldn’t really trust what I wrote…

I can’t seem to find the source I read this from, but if I remember correctly, caffeine works by binding to parts of your brain called adenosine receptors. Adenosine is responsible for regulating your sleep-wake cycle. However, just because these receptors are being taken up by the caffeine doesn’t mean that the adenosine is going away. It builds up in your system and you eventually reach a point where there is much more adenosine floating around in your body than there is caffeine, even if you drink more coffee. It eventually wins out, binds to the receptors, and makes caffeine less effective.

Caffeine doesn’t work instantly. It takes time to be absorbed into your blood and then to get to the brain. A coffee nap is a neat trick where you drink some coffee, take a 20 minute nap while the caffeine gets absorbed, then wake up really ready to go.

Caffeine works by bonding with the adenosine receptors in your brain. The trouble is, if your brain isn’t receiving adenosine like it is supposed to, it makes more receptors. So even though you’ve had your normal cup of coffee, you’re still feeling sleepy. So, of course, you have another cup of coffee, and the caffeine from *that* cup blocks the new receptors and you go on about your day. Which means your brain makes even *more* receptors.

In the meantime, the adenosine is just building up more and more, and when the caffeine goes away on its own the adenosine floods the now open receptors. And since you have more of them than you used to, you crash. *Hard*. This is where the withdrawal headaches come from. This can all happen over the course of a month.

The good news is the extra receptors go away after a week or so, so if you’ve reached the point where caffeine isn’t doing you any good take a couple of weeks off from it. I take a three week on, one week off approach, and I sleep better than I have in *years* as a result. Poop better, too.

Well everyone else gave you science answers, so I’m going to go a different route.

I have ADHD and stimulants calm me down so some people are just wired differently 🤷‍♀️