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