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How Caffeine Tricks Your Brain into Feeling Alert

Posted by Cassandra Collins on

How Caffeine Tricks Your Brain into Feeling Alert

TL;DR: You can thank a molecule in your brain called adenosine for the dreaded afternoon slump. Luckily, the caffeine in your cup of coffee tricks your brain by blocking adenosine, so you feel as wide awake as you did earlier in the day.

Here at Halo Neuroscience, we’re obsessed with figuring out how the brain works — and how we can optimize it to learn even faster with neurostimulation. But we know you can’t study the performance of the brain in isolation — there are a million different factors that affect how our brains perform. One of those factors is how the substances we consume (think coffee, alcohol, and medications) interact with the chemicals naturally found in our brains. Today, we explore how caffeine works to trick your brain into feeling alert.

Coffee—the morning miracle

If you’re anything like me and the rest of the Halo team, your day does not truly begin until the coffee kicks in. In fact, this survey found that over 64% of Americans start their day with a cup of coffee.

You’ve probably heard that the stimulating caffeine in coffee is what makes you feel more alert. But how exactly does caffeine take you from zombie to fully functioning professional?

It turns out caffeine’s mystical powers can all be explained by — you guessed it— neuroscience.

Adenosine—the molecules that makes you feel sleepy

To understand how caffeine works in the brain, you need to know a little bit about a molecule called adenosine.

Adenosine is a chemical that is present in every single cell in your body. You probably remember it from high school bio as ATP — adenosine triphosphate—a compound form of adenosine that your cells use as energy.

A molecule of ATP

But adenosine on its own doesn’t give you energy—it actually makes you feel sleepy.

When you wake up, adenosine starts binding to matching receptors in your brain just like a key fits into one specific lock. This starts to slow down your neural activity so you feel sleepy. As the day goes on, more and more adenosine binds to adenosine receptors — that’s why you feel sleepier and sleepier the longer you’re awake.

Neurofact: In official neuroscience lingo, adenosine is what we call an inhibitory neurotransmitter, meaning it works to inhibit, or decrease, activity in the brain.

Thankfully, when you sleep, your brain breaks down all that adenosine… so you should wake up feeling bright eyed and bushy tailed, right?

Not necessarily. If you don’t sleep for long enough, your brain won’t have enough time to clear out all the adenosine. That’s right, just what you needed—another reason to feel guilty about not getting those elusive 8 hours.

So just like how your blood alcohol content increases the more you drink, and then decreases slowly after you stop drinking, your adenosine levels rise the longer you stay awake, and then slowly decrease as you sleep.

Wait a minute, I thought we were talking about caffeine?

When you drink coffee, it gets dissolved into your bloodstream and enters the brain where all those adenosine molecules are hanging out.

Caffeine has the same basic “key” shape as adenosine, so it can fit in the same receptor “locks” in the brain that adenosine does.

Basically, caffeine fools adenosine receptors into thinking it is adenosine. 

But caffeine fails to make us feel sleepy like adenosine would when it binds to adenosine receptors.

So you get all these caffeine molecules filling up your adenosine receptors, blocking adenosine from binding to them and preventing you from feeling sleepy.

That’s why you feel more alert when you drink coffee — caffeine tricks your brain into thinking its adenosine-free just like when you first wake up.

Further amplifying caffeine’s alertness boost, all that unbound adenosine tells the adrenal glands to produce adrenaline. Plus caffeine increases levels of dopamine—that feel-good neurotransmitter you get lots of when do you something pleasurable like eat chocolate.

Neurofact: Caffeine is what we call an antagonist for adenosine. Caffeine blocks adenosine from binding to its receptors just like the antagonist (bad guy) of a story works against the protagonist (good guy).

Okay great! The more caffeine, the better.

Not so fast— caffeine dependency is real! As you drink more and more caffeine, your brain tries to compensate by making more adenosine receptors. The result it that you need to take in even more caffeine to block those extra adenosine receptors and get the same alertness effect.

This is how you get into a dependency cycle where you continually have to rev up your caffeine intake to match your increased number of adenosine receptors.

Don’t care if you’re dependent as long as you never have to sleep again? Don’t hook yourself up to an IV of Red Bull quite yet. Just because you don’t feel sleepy doesn’t mean that your brain isn’t tired.

Think about what you’ve heard about people with genetic conditions that prevent them from feeling pain — often these people end up hurting themselves because they don’t take proper precautions to avoid pain-inducing situations. Likewise, people who don’t feel tired get themselves into dangerous situations like driving a car that they normally would have avoided if they realized how tired they actually were.

So what should I do with this info?

At Halo, we know that our users care about performing their best at everything they do. So here are two action items for you:

  1. If you still feel sleepy after getting out of bed in the morning, chances are you didn’t give you brain enough time to wash out all that sleepiness-inducing adenosine. Try to get some more sleep!

  2. Use caffeine sparingly to fool your brain into thinking you’re not tired. But don’t trick your brain for too long, or you may end up caffeine-dependent—or worse—falling asleep at the wheel.


Not enough coffee in the world to give you that 25th hour you need to learn a new skill? Test Halo neurostimulation — if you don’t see results in 30 days, just send it back. We’ll even cover shipping.

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