What Caffeine Really Does To Your Brain

I recently stopped drinking coffee. Yeah, I know, why would anybody do that? For me it was a combination of health-related reasons, and overall I can say I’m happy I did. If you had asked me a few days after I kicked it, though, I would have told you it was one of the dumbest things I ever even thought of doing — that is, if my head stopped pounding long enough to answer you in a complete sentence.

This radical life adjustment made me curious about the effects of caffeine on the brain, so I did some research. The most surprising thing I found was that caffeine doesn’t really jack up the volume in our brain the way most of us think it does — the story about how our favorite drug works isn't nearly so straightforward.

First, what caffeine does not do.

Caffeine does not, by itself, make you a super productive, super fast, super talky jitter machine. That venti Café Americano is not the sole reason you’re able to cram six hours of work into 45 minutes, or that you’re shockingly charming between the hours of 8-11 a.m.

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What caffeine does do is one heck of an impersonation. In your brain, caffeine is the quintessential mimic of a neurochemical called adenosine. Adenosine is produced by neurons throughout the day as they fire, and as more of it is produced, the more your nervous system ratchets down.

Your nervous system monitors adenosine levels through receptors, particularly the A1 receptor that is found in your brain and throughout your body. As the chemical passes through the receptors, your adenosine tab increases until your nervous system pays it off by putting you to sleep.

The remarkable talent of caffeine is to mimic adenosine’s shape and size and enter the receptors without activating them. The receptors are then effectively blocked by caffeine (in clinical terms, caffeine is an antagonist of the A1 adenosine receptor).

This is important not only because by blocking the receptors caffeine disrupts the nervous system’s monitoring of the adenosine tab, but also because of the players who make an appearance as this is happening. The neurotransmitters dopamine and glutamate, the brain’s own home-grown stimulants, are freer to do their stimulating work with the adenosine tab on hold, and that’s the effect you feel not long after downing your triple shot skinny mochaccino.

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In other words, it’s not the caffeine that’s doing the stimulating. Instead, it’s keeping the doors blocked while the real party animals of the brain do what they love to do.

As every good coffee drinker knows, this effect lessens over time. It steadily takes more and more caffeine to achieve the same level of stimulation from your excitatory neurotransmitters. This is the irritating dynamic we all know as “tolerance.”

The reason it seems that coffee and tea became a morning ritual is that caffeine helps fight off the sleepy feelings we’re left with after a night of paying off a full adenosine tab. That’s something our favorite legal drug is quite proficient at doing.

What it’s not so good at doing, though we’d like it to be, is keeping us chugging away no matter how much sleep we miss. For a little while, it might seem like caffeine is warding off sleep deprivation, but the effect won’t last. Eventually, the nervous system wins (it pays to remember: the house always wins).

Of course, these effects vary depending on many things, including body type, weight, and age. For some, one cup of coffee will help kick things up; for others, it might take three cups. And as mentioned, tolerance of caffeine is a major variable no matter what source you prefer for your drug of choice.

So if you decide to kick the habit, how long will it take to work through withdrawal? That depends on how much caffeine you routinely consume, but for the average two or three-cup a day coffee drinker, expect up to 10 days of symptoms like headaches, fatigue and a general feeling of wanting to shout loudly into peoples' faces.

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David DiSalvo is a science and technology writer working at the intersection of cognition and culture and the author of What Makes Your Brain Happy And Why You Should Do The Opposite. Check out his website for more.