Caffeine is not just tea or coffee.
It is the main active ingredient in energy drinks, fat burners, chocolate, Coca-Cola, some desserts, and, of course, various types of coffee and tea.
It is caffeine that is responsible for the characteristic effects of these products, such as improved mood, stimulation of internal metabolism, and a surge of mental and physical energy 1-3.
Due to its effect on internal metabolism, caffeine can be beneficial for weight loss.
Scientific studies indicate that consuming caffeine in moderate doses poses no harm to health 4, but very high doses, especially overdose, can have unpleasant and even life-threatening side effects.
This is what we will discuss. Below, we will talk about the typical side effects of caffeine overdose, as well as try to understand what “moderate consumption” means and “how much is too much?”.
These questions are particularly relevant given the rapid increase in the range of caffeine-containing products on the market, their popularity, and the inherent difficulty in controlling daily dosage.
Main thoughts:
Side Effects of Caffeine Overdose
Scientific studies indicate that sensitivity to caffeine is individual and has a genetic predisposition. That is, some people can consume significantly higher doses of caffeine than others without negative health consequences 5,6.
Conversely, beginners whose bodies are not accustomed to caffeine may experience side effects at doses that are considered moderate 4,7.
Below we will discuss 9 side effects of caffeine overdose, the presence of which is a reason to reconsider your diet.
In moderate doses, caffeine poses no harm to health. Sensitivity to caffeine is individual and programmed in genes: side effects of overdose can manifest in different people at different doses
1 Irritability
A feeling of unwarranted anxiety is a well-known side effect of caffeine.
This occurs because caffeine blocks the action of adenosine—a chemical in the brain responsible for the feeling of fatigue. At the same time, adenosine stimulates the release of adrenaline—a hormone that increases energy 8.
In cases of caffeine overdose, these effects are amplified, manifesting as irritability and nervousness.
The American Psychiatric Association identifies caffeine overdose as one of the most common causes of psychiatric disorders related to irritability.
Overdose occurs at extremely high doses of caffeine (1000 mg or more).
Researchers state that even a moderate single dose of caffeine can lead to increased breathing rates and heightened stress levels 11,12.
In one experiment, it was shown that when 25 healthy men consumed approximately 300 mg of caffeine, their stress levels doubled compared to those who took a placebo.
Regular caffeine intake does not affect stress resilience: that is, both those who consume it occasionally and those who are avid coffee and tea drinkers are equally susceptible to its negative side effect of psychological instability 12.
To avoid caffeine overdose and its associated side effects, it is important to understand how much caffeine is actually contained in various types of coffee, tea, and other products.
For example, a large Grande coffee at Starbucks contains 330 mg of caffeine – that is, a third of the dose considered to be excessively high, at which the risk of overdose significantly increases.
We mentioned the caffeine content in some other popular drinks and fat burners in the article Caffeine for Weight Loss: Harm and Benefit.
If you notice irritability in yourself – reconsider your dose.
Caffeine overdose leads to psychological instability in the form of irritability and increased susceptibility to stress. Regular caffeine intake does not affect predisposition.
2 Sleep Disturbance or Insomnia
Caffeine is primarily known for its ability to invigorate and relieve drowsiness.
Caffeine overdose can make it nearly impossible to get a full night’s sleep, and thus recovery.
Scientific studies show that increased doses of caffeine increase the time needed to fall asleep, and can also reduce sleep duration, especially in older adults 13, 14.
At the same time, small and moderate doses of caffeine have virtually no negative side effects on sleep 15.
But remember the relativity of the concept of a moderate dose.
Many people who complain about poor sleep and problems falling asleep may not actually realize that they are consuming too large doses of caffeine.
It is important to understand that caffeine is not just coffee and tea. Coffee and tea are indeed among the most caffeine-rich natural products. Other sources of caffeine include energy drinks, Coca-Cola and other carbonated beverages, some medications, and fat burners.
For example, a serving of an energy drink contains an average of 500 mg of caffeine 16, just like a fat burner pill.
The dose of caffeine that affects sleep is individual and determined by genetics.
Caffeine intake in the afternoon is more likely to deprive you of sleep, as its effects last for several hours. Studies indicate that while caffeine remains in the body for an average of 5 hours, for some people the time period can be as short as 1.5 hours, while for others it can be up to 9 hours 17.
In one of the experiments aimed at understanding how caffeine intake affects sleep, 12 healthy adult volunteers consumed 400 mg of caffeine either 6 hours before sleep, 4 hours before, or right before bedtime. In all three groups, both the time taken to fall asleep and the time spent awake during the night significantly increased 18.
This indicates that to avoid the side effects of caffeine related to sleep disturbances, it is important not only to control the dose of caffeine but also the timing of its intake.
Caffeine provides a feeling of alertness during the day, but one of the characteristic side effects of its consumption is sleep disruption. The dosage is not the only factor; the timing of intake also matters.
3 Digestive Issues
One of the side effects of coffee noted by those who drink it in the morning is the unpleasant sensation of “movement” in the intestines.
This is explained by the fact that coffee stimulates the secretion of gastrin – a hormone produced by the stomach that activates intestinal function. Interestingly, decaffeinated coffee has the same effect, suggesting that caffeine may not be involved in this process 19,20,21.
However, according to research, caffeine can also stimulate active intestinal activity, increasing peristalsis – the wave-like contractions that help move food along 21.
Considering this side effect, it is not surprising that large doses of caffeine can lead to loose stools.
For many years, coffee has been blamed for contributing to the development of stomach ulcers, but recent large-scale studies involving over 8000 people do not confirm a relationship between them 22.
On the other hand, some studies suggest that caffeinated beverages (especially coffee) may worsen a condition where food from the stomach returns to the esophagus due to the relaxation of the muscles that prevent this (Gastroesophageal reflux disease) 23-25.
Small doses of caffeine improve gastrointestinal motility; in large doses, caffeine can lead to loose stools and the development of a condition where food returns from the stomach to the esophagus.
4 Muscle Tissue Breakdown
Rhabdomyolysis is a serious condition in which damaged muscle fibers break down and enter the bloodstream, subsequently affecting the kidneys and leading to impaired function.
The causes of this condition include injuries, infections, drugs, muscle overexertion, and bites from venomous snakes or insects.
There are several documented cases where excessive doses of caffeine have caused rhabdomyolysis, although they are rare 26-29.
In one case, a woman who drank 1 liter of coffee containing 565 ml of caffeine experienced side effects of rhabdomyolysis in the form of diarrhea, vomiting, and dark-colored urine. She managed to recover with the help of medication 29.
565 ml of caffeine is a very large single dose, especially for those who are very sensitive to it or do not consume it regularly.
To avoid rhabdomyolysis, it is recommended to take no more than 250 mg of caffeine per day.
Large doses of caffeine can lead to side effects in the form of the destruction of damaged muscle cells and their entry into the bloodstream, and then into the kidneys, subsequently impairing their function. To avoid this, take no more than 250 mg of caffeine per day.
5 Caffeine Dependence
Despite all the positive effects of caffeine consumption, it is a well-known fact that one of its side effects is the formation of dependence.
A thorough scientific investigation of this issue indicates that although caffeine, like cocaine and amphetamines, causes the release of certain chemicals in the brain, caffeine dependence has a different nature than that of classic drugs 30.
In large doses, caffeine forms psychological and physiological dependence.
One manifestation of caffeine dependence is a strong desire to consume it after waking up. If this does not occur, subjects experience impaired concentration and mental activity 31.
The frequency of caffeine consumption plays a role in the development of dependence.
In one study, 213 avid coffee drinkers were asked to describe their feelings after not consuming caffeine for 16 hours. Most of them reported headaches, fatigue, and other withdrawal symptoms 32.
Although caffeine dependence differs from drug addiction, regular consumption increases the likelihood of developing dependence on its positive effects.
Regular caffeine consumption leads to an addiction to its stimulating effects; disruption of regularity can lead to symptoms similar in nature to withdrawal.
6 Increased Blood Pressure
Caffeine, contrary to popular belief, does not increase the risk of developing cardiovascular diseases and heart attacks in most people.
However, some studies confirm that one of the side effects of caffeine is an increase in blood pressure, as it stimulates the nervous system 33-36.
High blood pressure is undoubtedly a factor that increases the risk of heart attack or stroke, as it can lead to damage to the arteries over time, which restricts blood flow to the brain and heart.
The effect of caffeine on blood pressure is temporary, i.e., it does not lead to chronic elevation.
Beginners, whose bodies are not accustomed to caffeine consumption, are most susceptible to the side effect of increased blood pressure.
Caffeine intake leads to an increase in blood pressure during exercise in healthy individuals 37.
To avoid negative side effects of caffeine on the heart, do not consume it in large doses and before training.
Caffeine increases blood pressure when consumed in large doses by healthy individuals before training or by beginners. This side effect is temporary.
7 Increased Heart Rate
The stimulating effect of caffeine causes the heart to beat faster.
There may also be arrhythmia in the form of atrial fibrillation. This effect has been observed in young people after consuming energy drinks containing very high doses of caffeine 39.
In one case, a woman who took an extremely high dose of caffeine in pill form in a suicide attempt developed very rapid heartbeat, kidney dysfunction, and some other health issues 40.
However, this side effect of caffeine is individual, and in some cases, even those with heart problems can tolerate extremely high doses of caffeine without issues.
In one study, 51 patients after a heart attack were given 100 mg of caffeine every hour for 5 hours: their heart rates remained stable 41.
The general advice is: if you experience heart rhythm disturbances when consuming caffeinated beverages, it is better to reduce the dose.
Large doses of caffeine can lead to arrhythmia in some individuals. This side effect is individual. If you observe it in yourself, it is better to reduce the dose.
8 Fatigue
Coffee, tea, and other caffeinated beverages are well-known energy boosters.
However, they also have the opposite side effect – feelings of severe fatigue and exhaustion after caffeine levels drop in the body.
One scientific review of 41 studies on this issue shows that although energy drinks containing caffeine increase concentration and attention, and improve mood for several hours, those who consume them very frequently feel much more exhausted than usual the next day 42.
Naturally, to avoid this side effect, one can have a cup of coffee the next day (similar to an alcoholic who drinks to cure a hangover) and do this regularly. But this, in turn, can lead to sleep disturbances and the development of caffeine dependence.
For maximum positive effects of caffeine and to avoid feelings of fatigue and tiredness, consume caffeine in moderate doses and avoid overdose.
Although caffeine is a known stimulant, its overdose can lead to a state of fatigue after its effects wear off.
9 Frequent urination
Frequent urination is a characteristic side effect of caffeine-containing beverages. The reason for this is the complex action of caffeine.
You may have noticed that after drinking coffee or tea, the urges to urinate become more frequent. This is also confirmed by scientific studies 43-45.
It seems that high doses of caffeine can lead to the development of urinary incontinence.
This is supported by a large scientific study on the causes of urinary incontinence in 65,000 women. Those who consumed 450 mg of caffeine per day had a significantly higher risk of developing incontinence compared to those who consumed less than 150 mg of caffeine per day 45.
If you drink caffeine-containing beverages and notice that you are running to the bathroom more often than usual, reduce your caffeine intake and see if the symptoms disappear.
Large doses of caffeine cause increased urination and can lead to the development of urinary incontinence.
Conclusion
Low and moderate doses of caffeine have positive health effects for most people.
Large doses and caffeine overdose can lead to side effects that not only affect quality of life but can also have serious health consequences.
Overall, the body’s reaction to caffeine is individual: what is normal for one person may be too much for another.
To enjoy the benefits of caffeine without unwanted side effects, consume it in moderate amounts.
Monitor your condition and try to notice the characteristic side effects of caffeine (sleep disturbances, fatigue and irritability, increased heart rate and frequency of urination, etc.) in time, which indicate that you should reduce your dose.
