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Why Does Caffeine Stop Working Over Time? · So That's Why

• 0:04
  Jen Oliver: Welcome to the, so that's Why podcast, where we unpack the
• 0:08
  science behind everyday questions.
• 0:10
  I'm Jen.
• 0:10
  Chris Smith: I'm Chris.
• 0:11
  Jamie Eynon: and, I'm Jamie.
• 0:13
  Jen Oliver: So tell me if this sounds familiar.
• 0:15
  You used to drink caffeine and feel like you could conquer the day, but
• 0:19
  now you drink it just to start feeling like you're running on a low battery.
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  Why does caffeine lose its magic?
• 0:27
  Jamie Eynon: Yeah, and it's especially noticeable with coffee.
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  There's a full on arms race going on.
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  You start with a single shot latte.
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  The next thing you know you're ordering a quadruple espresso
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  and the barista is looking at you like you need an intervention.
• 0:40
  Chris Smith: Totally, and it probably won't surprise you that nearly 90%
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  of adults consume caffeine daily.
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  Um, it's the most widely used psychoactive substance on the planet,
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  and yet most people have no idea why it gradually loses its punch.
• 0:52
  Jamie Eynon: And before we get into Jen, you are more of a tea person.
• 0:55
  Aren't you
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  Jen Oliver: Guilty as charged?
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  I'm a solid four cups of tea a day person, but I've noticed the same thing.
• 1:02
  You know, that first Brew of the morning used to give me like a proper lift,
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  but now it just feels like maintenance.
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  Chris Smith: That's because the mechanism is identical, whether it's coffee,
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  tea, energy, drinks, or cola, the molecule, doing the work is the same.
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  Caffeine tea has less per cup, typically, uh, 30 to 50 milligrams compared to about
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  95 milligrams in coffee, but your brain responds to it in exactly the same way.
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  So today we're talking about all caffeine, not just from coffee.
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  Jamie Eynon: Plus we'll get into why some people can drink espresso at 9:00
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  PM and sleep soundly while others are wide from a lunchtime cup, whether
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  you can actually do anything about it.
• 1:40
  Jen Oliver: So what's really going on here, because most
• 1:43
  people think caffeine tolerance, it's just a minor inconvenience.
• 1:46
  Chris Smith: They do, but it is much more than that.
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  In fact, a 2017 trial found that while caffeine still improved
• 1:53
  mental and physical performance after two weeks of daily use.
• 1:56
  Those benefits completely disappeared after one month of daily intake,
• 2:01
  Jamie Eynon: and that's a big deal though, isn't it?
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  If you are relying on a cup of coffee or tea to get through a busy morning
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  or power through a deadline, and it's basically doing nothing after a few weeks.
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  You're just going through the motions.
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  Jen Oliver: So the effects completely disappear after one month.
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  So every January when I set my, you know, new, new year, new me goals, my caffeine's
• 2:21
  already checked out before I have,
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  Chris Smith: I know, depression.
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  Right?
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  And here's where the part that like really gets people, because
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  research shows that once that full tolerance develops habitual caffeine.
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  Drinkers are essentially consuming it just to return to the baseline
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  they had before they started.
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  So without that morning cup, they'd actually feel worse than someone who'd
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  never touched the caffeine at all.
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  Jamie Eynon: So we're all locked in a cycle where our brew stops giving us
• 2:45
  a boost and just stops us feeling, or just stops us feeling terrible instead.
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  Jen Oliver: I mean, it's a pretty sobering thought for something we all
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  reach for first thing in the morning.
• 2:54
  But Chris, what is actually going on in our brains to cause this?
• 2:58
  Chris Smith: So to understand caffeine tolerance, we need to start
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  with a molecule called adenosine.
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  So throughout the day, your body produces this adenosine as a
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  natural byproduct of burning energy.
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  Adenosine binds to specific receptors in your brain, mainly called
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  the A one and A two A receptors.
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  And when it does, those receptors send you the signal you are tired, slow down.
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  Jen Oliver: So adenosine is essentially your brain's built-in brake pedal,
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  the longer you're awake and active.
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  The more adenosine accumulates and the stronger that signal
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  to be to rest becomes,
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  Chris Smith: that's it.
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  But what gets really interesting is that caffeine is structurally
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  almost identical to adenosine.
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  So when you drink coffee or tea, the caffeine molecules
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  slot into those same receptors.
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  But they don't activate them.
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  They just sit there blocking, adenosine from getting through.
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  Jamie Eynon: So the tired message is still being sent.
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  Caffeine is just stopping it from being delivered.
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  Chris Smith: Exactly right.
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  So think of it as like noise canceling headphones for your
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  brain's tiredness signals.
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  The noise is still there, but you just can't hear them.
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  Jen Oliver: Which is a really important distinction because that
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  means caffeine doesn't actually create energy or alertness.
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  It's just blocking your ability to feel tired.
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  So the adenosine is still building up in the background the whole time.
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  Chris Smith: Yeah, precisely.
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  And this is really the key to everything.
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  So your brain notices that it's tired signals.
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  Aren't getting through.
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  So it adapts by becoming more sensitive to them.
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  In fact, it does this by growing more adenosine receptors to compensate.
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  And a landmark study found that regular caffeine users increased adenosine
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  receptors in the brain by about 20 to 30%.
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  And another study showed that about 400 milligrams of caffeine per day, which
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  is roughly four cups of coffee for just 14 days, was enough to significantly
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  increase those receptors in humans.
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  Jamie Eynon: So your brain is basically hiring extra staff to handle the
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  complaints your coffee keeps ignoring.
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  Chris Smith: Yeah.
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  That's a great way of putting it.
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  And once those extra receptors are in place.
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  You now need more caffeine of course, to block a greater number of them.
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  The dose that once made you feel sharp now barely gets you back to normal.
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  Jen Oliver: And how quickly does this all happen?
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  Because it feels like a gradual thing.
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  But I can imagine the biology probably kicks in a lot faster than we'd expect
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  Chris Smith: it is it?
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  It's much faster once you read up it.
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  It's quite surprising.
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  In fact, one study found that complete tolerance to caffeine's
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  effects on blood pressure and heart rate occurred after just one to
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  four days of regular consumption.
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  The alertness and, uh, focus benefits last a bit longer, but a 2024 review confirmed
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  that measurable receptor changes occur within two weeks at moderate intake doses.
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  Jen Oliver: So within a fortnight, your brain's already restructured itself
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  to counteract your caffeine habit.
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  I mean, that's incredibly fast.
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  Jamie Eynon: And this explains the crash too, doesn't it?
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  Because I've noticed if I skip my afternoon coffee, I feel worse than if
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  I'd never had a coffee at all that day.
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  Jen Oliver: Mm-hmm.
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  Chris Smith: Yeah, that is spot on.
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  And it's one of the most counterintuitive parts.
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  'cause while caffeine, these occupying those receptors we talked
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  about, adenosine keeps accumulating.
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  So once the caffeine wears off and it's half-life is about.
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  Four to six hours, all that built up adenosine floods in at once.
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  So for chronic users, it's even worse because you've now got more
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  receptors than you started with.
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  So the tiredness signals hit harder than it would for a non caffeine drinker.
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  Jen Oliver: So habitual caffeine drinkers actually experience more fatigue without
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  it than someone who never drinks it.
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  I mean, that's quite the trade off.
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  Chris Smith: I know.
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  Depressing isn't it?
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  Um, a researcher described caffeine as a alone of the awake feeling rather
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  than the creation of any new energy.
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  So at some point you have to pay it back with interest.
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  Jamie Eynon: Caffeine is basically a payday loan for your brain.
• 6:44
  Good short term.
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  But the repayment plan is rough.
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  Jen Oliver: And the twist is that not everyone gets the same repayment plan.
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  Genetics play a big role in how caffeine affects different people.
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  Chris Smith: That's right.
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  And twin studies suggest it that genetics account for about 36 to,
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  I think 58% of the differences in how people respond to caffeine.
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  And there are two key genes involved here.
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  The first one is called the CYP one A two, which produces the enzyme
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  responsible for metabolizing about 95% of the caffeine in your body.
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  And a small variation in this gene can determine whether you
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  are a fast or a slow metabolizer.
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  So fast metabolizers down caffeine about one and a half or 1.6 times
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  faster than a slow metabolizer.
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  Jamie Eynon: So that friend who swears they can have an espresso
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  after dinner and sleep fine.
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  They're not making it up.
• 7:36
  Chris Smith: No, not at all.
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  And about 10% of the population carry a genetic variant, um, linked to
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  higher caffeine tolerance, and that allows them to consume larger amounts
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  later in the day without side effects.
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  The second gene called adora two A affects the adenosine receptor itself.
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  Different variations determine whether caffeine is more likely to keep you
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  awake or more likely to make you anxious.
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  Jen Oliver: So your entire relationship with caffeine, how much it wakes you
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  up, how quickly you build tolerance, whether it keeps you up at night,
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  is heavily influenced by your DNA.
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  So that explains why some people can drink caffeine late in the
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  day and feel fine while others are wired for hours after just one
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  cup in the afternoon, which is me.
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  That is me.
• 8:21
  Jamie Eynon: This explains every argument in every office, kitchen, ever.
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  How can you drink at 4:00 PM How can you not?
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  Turns out we're all just having a genetics debate and we didn't know it.
• 8:31
  Chris Smith: Totally.
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  And there's a myth worth addressing here.
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  I'm always the myth buster.
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  Jen Oliver: You are the Myth Buster
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  or Captain Sensible.
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  Chris Smith: I know so many people believe they've successfully adapted
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  to less sleep by using caffeine, but multiple studies show that while
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  you might feel less acutely tired.
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  The cognitive performance continually deteriorates.
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  So your brain is actually becoming numb to its own impairment.
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  Jen Oliver: So we touched on this in our sleep episode, the idea that
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  people can accumulate sleep debt without realizing how impaired they
• 9:00
  are, and then caffeine masks that even further, which is why it's such a trap.
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  Jamie Eynon: Uh, what about age?
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  I definitely feel like coffee hits differently now compared
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  to how it did in my twenties.
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  Chris Smith: No, absolutely.
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  So caffeine, metabolism slows with age, meaning it stays
• 9:14
  in your system for longer.
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  This is why many people find they can't tolerate a late afternoon
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  coffee as they get older.
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  They're not just imagining it, so their liver is simply processing it more slowly,
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  Jen Oliver: which explains why some people naturally switch to lower
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  caffeine like decaf tea over time, because lower caffeine per cup means
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  less impact on your sleep, especially if your metabolism slows with age.
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  Jamie Eynon: Alright, so the big question we actually, can we
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  actually do anything about this?
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  Or are we stuck in an endless cycle?
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  Chris Smith: Yeah, you can absolutely manage it.
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  And the most effective approach is strategic use of caffeine rather
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  than habitual use of caffeine.
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  So research shows that using caffeine on only days when you genuinely need
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  peak performance, let's say two to three days a week, prevents that steady
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  receptor buildup that causes tolerance.
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  Jen Oliver: And for people who wanna reset their tolerance, studies show that.
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  Brain receptor sensitivity.
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  It typically normalizes within about two weeks of stopping caffeine.
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  After a two week break, your sensitivity returns roughly to 70, 80% of its
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  original level, but heavy users obviously might need, you know, up
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  to two full months for a full reset,
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  Jamie Eynon: two weeks without coffee.
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  I think most people would rather live.
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  With weaker caffeine effects than deal with two weeks with no coffee.
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  Jen Oliver: Definitely.
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  Chris Smith: Uh, yeah, I think that's fair.
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  And there is a gentler option you can take.
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  So gradually reducing that caffeine intake by about 25% every 10 days,
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  that will produce significantly fewer withdrawal symptoms.
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  And research shows that about 80% fewer severe effects compared
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  to stopping abruptly for people.
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  Jen Oliver: It is also worth mentioning that caffeine withdrawal
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  is actually clinically recognized.
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  It's no joke is it?
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  You know, people experience symptoms such as headaches, fatigue,
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  irritability, difficulty concentrating, and those symptoms typically peak
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  a few days after, but then they do resolve within a couple of weeks.
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  Jamie Eynon: And that applies to tea drinkers too?
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  Chris Smith: It does, although tea drinkers often have a smoother
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  experience 'cause their daily caffeine intake tends to be lower.
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  If like Jen, you're on about four cups of tea a day, you're looking at maybe 150
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  to 200 milligrams of caffeine in total.
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  If you compare that to the same number of coffees like four a day,
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  that's closer to 400 milligrams.
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  So the withdrawal is proportionate to the intake.
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  Jen Oliver: I mean, that's reassuring.
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  So tea drinkers like myself might build tolerance more slowly.
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  And have a gentler time.
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  Resetting
• 11:41
  Chris Smith: generally yes, and keeping daily intake below roughly 200
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  milligrams, which is about two standard coffees or forties that slows the
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  rate at which that tolerance builds.
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  And one study found that 400 milligrams of caffeine daily for only seven
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  days, had no measurable receptor effect, but the same dose for 14 days.
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  Did.
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  So moderate tea drinking may sit in that sweet spot where you're getting
• 12:05
  some benefit without triggering those major receptor changes.
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  Jamie Eynon: So it's about finding that balance where you are getting the
• 12:11
  benefit without tipping into the zone where your brain starts remodeling.
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  Jen Oliver: And here's something else that's really interesting.
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  For anyone who exercises, caffeine still appears to boost physical
• 12:22
  performance, even intolerant individuals.
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  And a study showed that caffeine supplements, they enhance physical
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  performance by an average of around 11%.
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  So those that are habitual uses, they might need a higher dose, but the
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  benefit doesn't disappear entirely the way the mental alertness benefit does.
• 12:41
  Chris Smith: No.
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  And 11% is huge, isn't it?
• 12:42
  Jen Oliver: Mm-hmm.
• 12:43
  Chris Smith: But the catch is that caffeine improves performance.
• 12:45
  But can disrupt sleep.
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  And of course poor sleep undermines recovery.
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  So for anyone exercising regularly, the timing matters.
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  Ideally, no caffeine within about eight hours of bedtime.
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  Jamie Eynon: That's really interesting because.
• 12:59
  It creates a real tension.
• 13:00
  You want the performance boost, but not at the cost of your sleep.
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  Jen Oliver: And I think, uh, you know, most of us have probably been
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  in that cycle where we drink the caffeine to compensate for poor sleep.
• 13:10
  Then the caffeine disrupts our sleep, so then we need more the next day.
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  It's, it is the definition of a vicious circle.
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  Chris Smith: Yeah, it really is.
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  And, and it connects directly to what we discussed in previous episodes.
• 13:21
  So sleep quality affects everything.
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  Mood.
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  Cognitive function, uh, exercise recovery, even how your body manages inflammation
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  and caffeine tolerance sits right in the middle of all these systems.
• 13:33
  Jamie Eynon: Uh, and hydration too, right?
• 13:35
  If you're drinking four or five cups of coffee a day or tea because one
• 13:39
  doesn't cut it anymore, that's a lot of fluid moving through your system.
• 13:41
  Jen Oliver: Yeah, that's a good point.
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  At normal consumption levels, coffee and tea are both hydrating and we
• 13:46
  covered that in our hydration episodes.
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  But when tolerance pushes intake higher, it's worth being aware
• 13:53
  of your overall fluid balance.
• 13:55
  Chris Smith: Yeah, totally.
• 13:56
  And what is really striking is that caffeine tolerance is a
• 13:58
  perfect example of how our bodies constantly adapt to maintain balance.
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  And we saw the same principle with sweat acclimatization, with sleep cycles,
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  even with cholesterol regulation, the body's always adjusting and adapting.
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  Jamie Eynon: So understanding this isn't just about coffee, it's about
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  us understanding how your body works.
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  Full stop.
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  Jen Oliver: So why does your morning coffee or tea stop working?
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  Chris Smith: It stops working because your brain physically adapts to
• 14:27
  caffeine by growing more adenosine receptors, sometimes 20 to 30% more.
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  The dose that once blocked enough receptors to make you feel alert now
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  can't keep up with increased numbers.
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  You end up drinking caffeine just to feel the way you would naturally without it.
• 14:42
  Jamie Eynon: So we went from one cup making us feel super human to four
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  cups making us feel merely human.
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  And we've been calling that a coffee habit when it's actually
• 14:50
  a brain renovation project.
• 14:53
  Jen Oliver: So that's why caffeine stops working, and now you know that your
• 14:57
  relationship with it is shaped by your genetics, your habits, and your brain's
• 15:02
  relentless drive to maintain balance.
• 15:05
  But the good news is once you understand the mechanisms, you can
• 15:08
  work with it rather than against it.
• 15:11
  Chris Smith: You can.
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  And the advice is to use caffeine strategically, not habitually.
• 15:15
  So a periodic reset or simply cutting back can restore much of that original effect.
• 15:20
  Sometimes less really is more.
• 15:22
  Jen Oliver: So that's it for this week.
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  Make sure you hit that subscribe button.
• 15:26
  We're unpacking the science behind everyday questions each week,
• 15:30
  and tell us in the comments what questions you'd like us to explore.
• 15:34
  Thanks for geeking out with us, but for now, that's it from me.
• 15:38
  Jamie Eynon: That's it from me.
• 15:39
  Chris Smith: And that's it from me.
• 15:41
  Jen Oliver: Bye for now.