Caffeine Overdose: Top 11 Symptoms You Need To Know

Maybe you can’t start your day without it. Maybe you need it to get you through the afternoon slump.

Or maybe it’s saved you during many nights of studying or working (or partying).

So many of us rely on a little caffeine kick to get started or keep us going throughout the day.  

But when does a good thing become a bad thing?

It’s important to listen to the warning signs your body gives you that let you know when something good for you becomes unhealthy.

If you are showing several of the following symptoms at once, you may have had too much caffeine.

#1 Increased Heart Rate/Palpitations

You might experience that racing feeling in your heart, an irregular pulse, a feeling like your heart is skipping beats, or flip-flopping around your chest.

Increased Heart Rate

You probably already know that caffeine is a stimulant—it gets your heart to work harder and that gets your blood flowing to your organs and muscles faster, helping to give you that extra boost of energy (1). 

That doesn’t sound so bad, after all the same thing happens when we are exercising.

But the difference here is the sustained amount of time that caffeine is making your heart beat so hard—possibly several hours—and you can’t control it the same way as when you exercise.

Your heart has to work continuously to keep up with the stimulation until it works its way out of your body.

If you find that your heart rate doesn’t go back to normal or the symptoms are severe, you may need to see a doctor (2).

#2 Jitters and Restlessness

You, like many of us, might find caffeinated drinks to be an awesomely delicious way to get some extra energy, and that boost can feel great.


Yet too much caffeine can put your body over the edge so to speak.

That stimulation from caffeine gets hormones like adrenaline to pump out more into your body, and too much adrenaline can make you start to get jittery or shake (3). 

Think of it as a similar effect to when you are frightened—you get an extra shot of adrenaline and you might shake or feel jittery from the “nerves” (4). 

The caffeine also quickly gives your body an overabundance of energy that it can’t use, causing you to feel “buzzy” with energy.

Pretty impossible to get into a restful state under those circumstances, instead you can become restless or even hyperactive from the caffeine.

This heightened and extended state can put a strain on your nervous system, especially your adrenals, causing them to become fatigued (5).

#3 Anxiety

That caffeinated coffee or tea can be soothing, and so some people drink them to help cope with stress.


However, an overdose of caffeine can have the opposite effect.

We’ve already discussed how it can get your central nervous system in a bit of a tizzy, and that extra adrenaline puts your body into a “fight or flight” mode—like when your scared, it’s the thing that instinctively makes you either flee from danger or fight for your life (6). 

It’s a heightened state of anxiety (7). 

The caffeine also affects your body’s release of dopamine, the hormone in your brain that gives you happy feelings and helps to regulate anxiety and inhibits the flow of the neurotransmitter GABA which helps to keep your brain calm (8). 

As you might expect, the anxiety levels found in men and women due to a caffeine overdose differ, and a small study found that an uptick in anxiety was more often seen in men (9).

#4 Mental Confusion

Isn’t caffeine supposed to make you more alert and sharpen your thinking?

For many it does, and often people feel that their brain is muddled when they don’t have their coffee.

Mental Confusion

But having an overabundance of caffeine can have the opposite of the desired effect.

Caffeine is considered to be a psychoactive substance which means that it affects the thinking part of your brain, altering your thoughts and mood (10). 

Instead of making your brain clear, too much caffeine can cause your thoughts and speech to ramble (similar to drinking a bit too much alcohol) or cause you to feel depressed.

In fact, the American Psychiatric Association has labeled this effect as one of four caffeine-related disorders.

These symptoms including the anxiety we mentioned in the previous point, can be easily confused for a mental disorder (11).

So it’s important to look at or let your doctor know any other symptoms you might experience in order to determine whether these are related to caffeine toxicity.

#5 Hallucinations

Being that caffeine is mind-altering as we just talked about, an overabundance can cause your brain to have trouble distinguishing reality, possibly causing you to see and hear things that aren’t real.


In study of what happens to your brain on excessive caffeine, people were exposed to the sound of white noise (that static-y sound on old radios and TVs) but claimed that they heard the song “White Christmas” playing (12). 

It’s thought that this symptom could be caused by a lot of caffeine boosting your body’s stress hormone, cortisol, and these high-stress levels can cause visual or audio hallucinations.

As much as this might be somewhat unnerving if you’re experiencing it, this isn’t usually considered to be serious unless it interferes with your daily life.

It is worth mentioning though that long-term stress has some serious impacts on your body, even if those stress spikes are from too much caffeine (13).

#6 Insomnia

Besides increasing the flow of adrenaline which keeps your body and mind from being in a restful state, caffeine messes with the brain chemicals (melatonin and adenosine) that let your body know when it’s time to go to sleep (14).


So it tricks you into staying awake instead of letting you feel sleepy, kind of like leaving the light switch in your brain stuck in the “on” position (15).

Many of us might cut ourselves off from the caffeine earlier in the day, having too much caffeine, even in the late afternoon or early evening can still be affecting your ability to fall into a nice restful sleep, or even sleep at all.

Research shows that it can take a normal amount of caffeine 6 hours to leave the body, though some studies show that it can keep your brain awake for up to 9 hours, which is more likely the effect you’ll get with an overdose (16).

It’s easy to underestimate just how much caffeine you’ve had, or how late you can keep drinking without it affecting your sleep (17). 

Try cutting out the caffeine earlier in the day to help your body get sleepy when it needs to.

#7 Increased Thirst

Anyone of us who drink a lot of caffeinated beverages knows the effects it can have on our bladders (18). 

For years caffeine has been said to be a culprit in dehydrating your body, but that is a little misleading.

Increased Thirst

It’s not actually the caffeine that dehydrates your body, but high amounts of it have a diuretic effect, aka it makes you pee a lot.

All that caffeine stimulation doesn’t just affect one part of your body, it’s going to hit your kidneys as well.

And being that the caffeine is a foreign substance, your body is going to do what it takes to get it out, especially when there is too much of it (19).

So, when you end up peeing a lot, you lose too much water and salt from your body, and that is what makes you dehydrated and thirstier than normal (20). 

With all that heart pumping, blood pressure raising, and adrenaline flowing, an overdose of caffeine can get you’re your sweat glands into the action.  

This sweatiness can further contribute to your body’s dehydration and need to drink water (21).

Of course, if you’ve been out in the sun and you’ve had a lot of caffeine, it’s going to worsen the dehydration and your thirst will be more urgent.

If you experience this symptom, make sure you’re turning to life-saving water to help you out, not more caffeinated drinks.

#8 Diarrhea

Surprise, caffeine stimulates your digestive system as well.

Acid producing caffeine sends signals to your body to produce more bile, the stuff that helps break down waste and get it ready to go out.


Too much bile caused by an overdose of caffeine builds up and can contribute to diarrhea.

The caffeine also causes your intestines to expand and contract faster (they’re overstimulated, too) causing a laxative effect on your system.

Although it’s not completely understood by the medical community a high amount of caffeine has this effect on your urge to go, but our digestive system is pretty sensitive, so generally, your body will tell itself that what goes in must go out.

This is especially true if it wants to get rid of too much of a foreign substance like caffeine (22). 

Especially when combined with all that peeing, diarrhea can further dehydrate your body.

#9 Heartburn, Nausea, and Vomiting

Too much caffeine can have other quite unpleasant effects on your digestive system.

When an excess of caffeine hits your stomach, some funky things can start to happen.


Your stomach is already full of acid and caffeine just piles it on.

This excess irritates the muscle at the end of your esophagus, making everything in your stomach, including the acid, start to flow upward, causing that burning sensation in your chest and esophagus (23). 

All that acid also irritates your stomach lining which can leave you feeling queasy.

Although most people only experience nausea, there are some people who end up vomiting from too much caffeine intake.

Coffee, being the diuretic that it is, means that it’s going to cause your body to give up its fluids, and you don’t always get to choose the most pleasant way for that to happen (24).

#10 Headaches or Migraines

When it comes to headaches, caffeine can be a double-edged sword.

A moderate amount of caffeine can be used to help ease headaches, in fact, a number of over-the-counter migraine medications include caffeine.


It’s also possible that caffeine affects the neurotransmitters in your brain that help block head pain (25). 

So then why might you suffer from a headache after drinking too much caffeine?

It’s not actually the caffeine that is causing the headache.

Caffeine constricts the blood vessels in your head and when it’s gone out of your system, they expand again.

Your blood vessels expanding back to their normal size is what can cause you to have a headache, also known as a rebound headache (26). 

If you’re in the habit of grabbing a cup of coffee or caffeine-laden painkillers whenever you get a headache.

It’s important to recognize whether your headache is a symptom of too much caffeine so you can treat it with non-caffeinated pain relievers. 

#11 Fatigue

Since we’ve beaten you over the head with the fact that caffeine is a stimulant that keeps you alert and awake, it might seem a bit crazy that fatigue is a symptom of a caffeine overdose.


But the fatigue you’re feeling after having a lot of caffeine is also a rebound effect—it wasn’t directly caused by the caffeine, but it was a result of it leaving your body.

When your body is tired, caffeine can give you a false energy.

It can be awesome to have so much energy to get what you need to be done, but ultimately, it’s only masking the underlying tiredness and the reasons why your body is tired.

Caffeine is only a temporary fix and in the long run, it can stress your adrenals which will leave you chronically fatigued.

So, if your body is tired, get it the rest it needs (27). 


We hope that you found this list helpful, and you may have even recognized some of the symptoms we’ve talked about.

It’s important to take care of your body—you’ve got it for the long haul.

So many of us have become reliant on caffeine to function, to the detriment of our own health and ironically, our ability to function sometimes.

We’ve done plenty of talking, now we want to know what you think.

Please share a comment below or share this article with someone who might benefit.

My name is Kathy Gallo, Editor of Daily Cupo, a Coffee buff. The guide you find here is designed exactly for you, and it is our hope that you find it not only interesting but also actionable.

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