Why does coffee make me sleepy?

15 October 2013

Question

Why is it that when I drink coffee it can make me more sleepy? Other people seem to drink coffee and wake up!

Answer

We posed this question to the brain panel...

Mike - It depends on the time course. I'd be surprised if somebody would drink a cup of coffee then immediately feels sleepy. But I think it's perfectly reasonable to feel sleepy a little bit later on because, what's happening when you drink coffee, is that caffeine blocks the action of a "tiredness transmitter" in the brain called adenosine.

Adenosine progressively damps down brain activity as it accumulates during the day, contributing to sleepiness. When we go to sleep, the adenosine is flushed out from the brain again so that we feel rested and refreshed when we wake up.

If you block the effect of adenosine with caffeine, then you will feel more awake. But, later on, when the coffee effect wears off after it gets eliminated, which takes 4 hours or so, the adenosine is still there, and then that may kick in and make you feel sleepy. But I don't know of a circumstances where you would drink coffee and then suddenly feel sleepy.

Bill - Except, perhaps, if you had a strong association with coffee as a thing that you took next to going to sleep. Like children hear nursery melodies and they're put to sleep by it. If you had a routine in which you drank coffee and then went to sleep, it may be a signal to sleep and would help you get to sleep. Is that possible?

Hannah - Or maybe he associates coffee with incredibly boring activities like being in the office?

Katie - Feeling really tired?

Comments

I'm 23 and every time i have tried coffee no matter where it was, at school, an important event i needed to stay awake for or my friends house i have fallen asleep within 20 minutes and i will stay asleep for around 16 hours. Coffee to me is like strong sleeping pills. So many people drink coffee so it comes up in my daily life alot. Every time i tell someone "i dont drink coffee because it puts me to sleep" they ask me if i have ADHD. Which i dont know. Is this something that only happens to me?

Hi - This also happens to me sometimes. Most of the time I can drink coffee and it will keep me awake, even hours later. But sometimes - especially when drinking coffee at a diner - I will get immediately drowsy and if it is a day off, I fall asleep within about half an hour and will sleep for an hour or so. So, like the 2 ladies before me, I'm not talking about coffee in the morning and then a crash in the afternoon - there's something about the coffee that makes me sleepy. My own hypothesis is that the particular batch has less caffeine in it, and the "hot milk" from the cream I put in it makes me drowsy.... But I don't think this is so because it often happens (BUT NOT ALWAYS) after drinking it in a restaurant and putting that fake cream in it, which is all most places seem to offer any more. It seems like there's no simple answer for this apparently common phenomenon.

I can drink two 20ounce cups of coffee in the morning, I put ice in it directly so it won't be so hot, but I can lay down as soon as I finish my second cup , and that's usually around 5:30 or 6:00 am and go right to sleep.im not sure why or how, but I'll prove it to anyone that wants to see.

Coffee definitely makes me sleepy, not 4 hours later, immediately after I finish a cup. By sleepy, I mean, I'm likely to go to sleep, if I'm not working and it's my free time. I've been drinking about 5 cups of coffee a day for my whole life, maybe that's the reason. Would love to know why.

When I drink coffee (doesn't matter how it's made or what's in it), I immediately feel a headache coming on and then get very tired. I once fell asleep while in college after I drank a large cup from Starbucks with the intention of staying awake. I wonder why it affects me so differently.

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