Why Does Caffeine Make Me Tired? 8 Reasons That Explain It

Ever reach for an espresso hoping to perk yourself up, only to get to the bottom of the cup feeling more drowsy than before? Or what about turning to an energy drink to get you through an all-nighter only for your eyelids to keep on drooping? 

One of the most well-known effects of caffeine is that it can wake you up, but it doesn’t always do the trick. In fact, you may find yourself even more tired after a cup of joe than before you started drinking it. 

However, while caffeine can certainly affect your sleep – and therefore your energy levels the next day — it may not be the caffeine itself that’s making you feel tired.

Below, we’ll dive into the many reasons why you may be feeling tired, even after drinking a coffee. Plus, more importantly, we’ll explain how to fix them. 

Want to master the art of consuming caffeine? We’ve answered every question you could have about caffeine, sleep, and energy here.

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Tired (pun intended) of wondering what’s causing your caffeine crash? Here’s why caffeine may be having the opposite effect you’re looking for. 

1. You Can Feel the Effects of Adenosine Again 

Adenosine is naturally made in the body and acts as a neurotransmitter, depressing the central nervous system and telling the brain when to rest. Its rate of production outpaces its rate of removal during the time we’re awake, eventually reaching the point where it makes us feel drowsy and we feel the urge to sleep. When we sleep, it’s purged from our system, so we wake up with much lower adenosine levels, starting the cycle over again. This is one way our sleep-wake cycle is regulated. 

Caffeine changes things, however. It binds to the adenosine receptors in your brain, meaning caffeine blocks adenosine from doing its job, so you won’t feel the drowsiness effects of the chemical in your system. But the buildup of adenosine continues all the time you’re awake. So, when your body metabolizes all the caffeine you’ve had, and adenosine can bind to those receptors again, you’ll not only feel all the tiredness you had before, but all the extra tiredness that’s been building up, too. 

This is why you may feel more tired when caffeine wears off compared to when you first consumed it. It’s not the caffeine causing it, though. It’s your body’s natural build up of sleepiness. 

However, research suggests people who regularly consume caffeine have an increased number of adenosine receptors and therefore become more sensitive to the sleepiness adenosine makes you feel. Once caffeine wears off and adenosine can do its job again, you’ll feel a rush of tiredness and the strong urge to grab another coffee. 

2. You’ve Got High Sleep Debt

Sleep debt is the measure of how much sleep you owe your body over the last 14 nights. It’s measured against your sleep need, the genetically determined amount of sleep you need. What does that mean in real world terms? Let’s look at an example. 

If your sleep need is 8 hours and 30 minutes, but you’ve been getting less than 7 hours a night, you’ll have built up quite a bit of sleep debt. 

This sleep debt affects everything from your mood to your productivity to your mental and physical health. But it also simply makes you feel tired throughout the day — and no amount of coffee can fix high sleep debt.

Caffeine can work as a pick-me-up, of course, but it only temporarily masks how tired you feel. So, if you’re finding yourself feeling more tired after a coffee, it may simply be your sleep debt catching up with you. This is made worse if you repeatedly reach for caffeine instead of catching up on sleep. 

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3. You Have Caffeine-Related Sleep Loss 

As we explained above, high sleep debt may be the reason why you’re feeling so sleepy. But caffeine may actually be making this worse. If you have too much caffeine too close to bedtime, it’ll hugely impact your sleep. With caffeine temporarily blocking your adenosine receptors, you may not feel sleepy until much later, and therefore you’ll likely stay up much later than your body naturally wants you to. 

A 2023 meta analysis on the effect of caffeine on subsequent sleep found caffeine consumption reduced total sleep time by 45 min and sleep efficiency by 7%, with increases in sleep latency and time spent awake at night. Light sleep also increased at the expense of deep sleep.

With less sleep, your sleep debt will only get worse, meaning you’ll feel more tired the next day and be tempted to increase your coffee consumption even more — and the vicious cycle continues. 

And caffeine lasts in your system much longer than you think. Caffeine has a half-life of three to seven hours — this is the amount of time it takes for your body to break down half of the caffeine in your system. Everyone metabolizes caffeine at different rates, but it could last for 12 hours, meaning your lunchtime latte could still be lingering around midnight, pushing back when you feel sleepy.  

We’ve covered more on how long caffeine lasts here. 

But even when caffeine wears off, you may still struggle to fall asleep and meet your sleep need. That’s because you’ve missed your Melatonin Window. In the RISE app, this is the roughly one-hour window of time when your brain is making the most of the sleep hormone melatonin it will all night. If you get to sleep within this window, you’ll have a much easier time falling and staying asleep. 

If you miss it though, because you’ve been kept awake by caffeine, you may find it harder to drift off. This, of course, leads to more sleep debt the next day, and more tiredness, even if you consume caffeine. 

4. You’ve Developed Caffeine Tolerance  

Caffeine may not be making you feel tired, it just may not be making you feel as awake as it used to. That’s because your body can actually develop a tolerance to it, meaning you need more and more to feel the same stimulating effects. 

If you don’t up the amount of caffeine you have, you may start feeling the effects of sleep debt or even just general adenosine building up over the day, where caffeine used to mask this. 

It’s a slippery slope, though. If you start reaching for more caffeine, to try and feel the same effects of coffee, for example, you run the risk of struggling to fall asleep at night, not meeting your sleep need, and then feeling more tired the next day. 

5. You’re in a Natural Energy Dip

Our energy levels naturally fluctuate throughout the day as part of our circadian rhythm — our internal body clock that runs over a roughly 24-hour cycle. So, even if we’re not sleep deprived, we’ll still feel periods of higher and lower energy. 

One of these periods of lower energy comes in the afternoon. You’ll feel it more and for longer if you’ve got a lot of sleep debt, but even those of us who are all caught up on sleep will feel a bit more sluggish and low on energy during this time. 

What does coffee have to do with this? Well, even if you’ve had a caffeinated drink recently, you may be experiencing tiredness as part of this dip in energy. 

The RISE app predicts your circadian rhythm and takes into account how long and what times you slept the night before to tell you when these energy peaks and dips will be each day.

6. You’re Experiencing Withdrawal Symptoms

It may sound counterintuitive to be experiencing withdrawal symptoms, while still consuming caffeine, but research shows you don’t need to have cut out caffeine altogether to feel withdrawal. 

For example, one study found when people who were used to consuming 300 milligrams of caffeine cut down to 200 mg or less, they experienced withdrawal symptoms. And while 100 mg of caffeine sounds like a lot, that’s equivalent to about one 8-ounce cup of coffee. So, if you’re used to drinking four cups of coffee a day, and you go down to three, this may be the reason why you’re feeling tired — it’s the withdrawal symptoms not the coffee itself. And you may start feeling these symptoms 12 to 24 hours after your last sip of coffee, but it can happen sooner.

Caffeine also triggers adrenaline and the stress hormone cortisol, so without these, you’re left feeling less alert and awake than you’re used to.  

Symptoms of caffeine withdrawal includes: 

• Fatigue 
• Headaches 
• Depressed mood 
• Difficulty concentrating 
• Brain fog 

We’ve covered how long caffeine withdrawal symptoms last here. 

7. You’re Experiencing a Sugar Crash 

Most of us don’t only drink black coffee, so it may not be the caffeine in your drink that’s making you feel tired, it may be the sugar. This is true if you add sugar, sweeteners, or flavored syrups to your coffee drinks, or if you drink sugary soft drinks and energy drinks. 

And it may not even be the sugar in your caffeine. If you regularly drink coffee with a sugary breakfast, or sip a soft drink with a lunch of simple carbs, you may experience a sugar rush and then sugar crash from these things instead. 

Your blood sugar levels spike shortly after eating and drinking simple sugars, only to crash a few hours later, leaving you feeling more tired than ever.

Symptoms of a sugar crash include: 

• Fatigue 
• Headaches
• Irritability 
• Difficulty concentrating 
• Hunger 

8. You’re Dehydrated 

Caffeine is a diuretic, or something that makes you pee more often than usual. So, one theory for why caffeine makes you feel tired is that it can dehydrate you, as you’re losing liquids at a faster rate. And one of the most common symptoms of dehydration is fatigue. 

Caffeine increases blood flow to the kidneys and stops the reabsorption of sodium, magnesium, and calcium, which makes you expel more water. Plus, caffeine may stimulate the muscles in the bladder responsible for contracting and expelling urine.

However, not all scientists agree caffeine has this effect. A meta-analysis looking at several caffeine studies found consuming up to 400 mg per day — about the same as four cups of coffee — did not cause dehydration. 

However, when caffeine intake is higher, it may cause dehydration. One study had participants consume about 4 mg of caffeine per pound of bodyweight. Their urine increased by about 14 fluid ounces compared to those taking a placebo. 

You may feel these dehydrating side effects more if you haven’t had caffeine for a few days. One study had participants drink six cups of coffee after being deprived of caffeine for five days. Their urine output increased by about 25 fluid ounces over the four hour trial, causing dehydration. 

But the effect may wear off quickly. Another study in the same meta-analysis found urine output increased on day one, but not on day two or three of the study, showing that you may become tolerant to caffeine's diuretic effects.

Another theory is if you’re regularly reaching for coffee, tea, energy drinks, and caffeinated soft drinks throughout the day, you’re less likely to be reaching for water, too, which could lead to dehydration and therefore fatigue. 

So, now you know the many reasons why caffeine may be making you feel tired, it’s time to fight against them. 

There are some easy fixes like:

• Reduce the amount of sugar you have with your caffeine 
• Make sure you’re staying hydrated 
• Ride the withdrawal symptoms until they pass – this could be up to nine days

Long-term fixes to drastically improve your energy levels include: 

Pay Down Sleep Debt

The RISE app can calculate how much sleep debt you have. We recommend keeping this below five hours to feel and perform your best each day, and to reduce daytime drowsiness. If you find you’ve got a lot of sleep debt, you can pay some of it back by: 

• Taking a nap 
• Waking up a little later
• Going to sleep a little earlier 
• Maintaining good sleep hygiene — this helps you fall asleep faster and wake up less often during the night, therefore getting more sleep overall   

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Honor Your Caffeine Cutoff Time

If you’re struggling to fall asleep at night, and experiencing tiredness the next day, being a coffee drinker may be to blame. But that doesn’t mean you have to cut out all caffeine consumption altogether – you just need to honor your caffeine cutoff time.

This is the time of day when you should stop consuming caffeinated drinks — or anything else containing caffeine — to give your body enough time to break it down before bedtime. Most people’s cutoff time will be around noon, although night owls might be able to consume caffeine up until about 2 p.m. 

This time will be different for everyone, and it can change each day as it’s based on the timing of your circadian rhythm. RISE can take the guesswork out of it by predicting your unique cutoff time each day, and reminding you when you should have your last sip of coffee or tea 10 hours before your Melatonin Window. 

But remember, it’s more than just caffeinated beverages, chocolate – especially dark chocolate – contains caffeine. And even decaf coffee contains it too, even if it is in lower quantities. 

Sync Up With Your Circadian Rhythm 

We mentioned how you may be in a natural energy dip when feeling tired in the afternoon. RISE can tell you when these are coming by showing you a prediction of your energy cycle each day. This way, you can try to schedule demanding tasks for when you’ll have more energy, and save easy tasks for your dip in energy, or simply use this time to rest (or take a nap if you’re trying to pay back some sleep debt). 

Beyond staying in sync with your energy peaks and dips, you can also use RISE to check the timing of your Melatonin Window each day, and aim to go to sleep in this one-hour window. This will help you fall asleep more easily and stay asleep all night, meaning you’re much more likely to meet your sleep need and feel much more energy the next day. 

Boost Your Energy Levels With RISE 

There are many reasons why caffeine may be making you feel tired – like keeping you up later than usual – but there are also many reasons why it may not be the caffeine at all – think sleep debt and being in a natural energy dip. 

The RISE app can help boost your energy, whether you decide to drink coffee or not. It can tell you your ideal caffeine cutoff time each day, so your daily coffee habit won’t impact your bedtime. The app can also calculate how much sleep debt you have, and keep track of it as you work to pay it back, and predict your energy cycle each day, so you know when those dips in energy are coming. 

With all this knowledge at your fingertips, you can boost your energy levels and reach your full potential each day. 

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Your Caffeine Questions Answered:

• When should you stop drinking coffee?
• How long does caffeine last?
• How long does caffeine withdrawal last?
• How much caffeine is too much?
• How to get energy without caffeine
• Why doesn't caffeine affect me?
• Why do energy drinks make me tired?
• All of your sleep, energy, and caffeine questions answered (in one place)

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