This article was written by Dr. Babar Naeem (MBBS, MRCPCH) – a licensed and practicing medical doctor – to ensure maximum factual accuracy and unique content.
Caffeinated drinks are a popular way to increase alertness to improve mental and physical performance.
However, because caffeine is a stimulant that reduces tiredness, these drinks can make it harder to get to sleep.
Furthermore, it can be difficult to know exactly how much caffeine is in various types of drinks and how long the caffeine will stay in your system to the point of keeping you awake.
So how long does caffeine stay in your system and keep you awake?
Caffeine stays in your system for up to 10-12 hours. Half of the caffeine will be out of your system after around 5-6 hours, with maximum concentration in the blood occurring after around 1 hour. 100mg of caffeine (1 cup of coffee) can keep you awake for between 4 and 10 hours depending on your tolerance.
In the rest of this article, I have used my knowledge as a medical doctor and my access to research papers to provide you with a detailed list of the caffeine content for the most popular caffeinated drinks and how long they are likely to keep you awake.
I have also explained in more detail the personal factors that explain why caffeine is more likely to keep certain individuals awake than others.
I have also included a section that explains how to get caffeine out of your system quickly so that you can get to sleep.
The Effects of Popular Caffeinated Drinks on Wakefulness
The table below summarizes the amount of caffeine found in the most commonly consumed caffeinated drinks and the approximate amount of time the caffeine will stay in your system and keep you awake:
|Caffeine Source||Approx Time of Wakefulness|
|1 cup of coffee (100mg/8oz cup)||4-10 hours|
|1 cup of black tea (47mg/8oz cup)||2-5 hours|
|1 cup of chai tea (26mg/8oz cup)||1-2.5 hours|
|1 cup of green tea (33mg/8oz cup)||1.3-3.3 hours|
|1 cup of iced tea (26mg/8oz cup)||1-2.5 hours|
|Coca Cola (30mg/12oz)||1.2-3 hours|
|Diet Coke (47mg/12oz)||2-5 hours|
|Full Throttle (108mg/12oz)||4.3-10.8 hours|
|Monster (120mg/12oz)||4.8-12 hours|
|Mountain Dew (55mg/12oz)||2.1-5.4 hours|
|Regular Pepsi (37mg/12oz)||1.5-3.7 hours|
|Red Bull (114mg/12oz)||4.6-11.4 hours|
Coffee: 100mg Per 8oz Cup (4-10 Hours of Wakefulness)
The caffeine content of coffee can vary greatly depending on the preparation, but on average it contains approximately 100mg per 240ml (8oz) cup of coffee, and because approximately half of the caffeine will still be in your system 5-6 hours later, sleep may not be possible for up to 12 hours after consumption – depending on your sensitivity and consumption volume.
However, because the level of caffeine in the body starts falling after 5-6 hours, it is reasonable to go to bed 4 hours after drinking coffee – although sleep may not be possible until up to 12 hours have passed.
McCusker and his colleagues did a very interesting study in 2003.
They purchased coffee from 20 different stores in the United States, and measured the caffeine content of each, with the help of advanced chromatographic techniques.
The caffeine content of a single cup of coffee was found to be anywhere between 58 and 259 mg.
In the same study, they also measured the caffeine content of coffee purchased from the same store at different times.
They found that caffeine content could vary from 130 to 280 mg per cup .
Espresso has a very high caffeine content of 480 to 600 mg per 8 ounces.
So a small serving size of 1.5 to 2 ounces is usually safe, but it can be dangerous if taken in large amounts .
As the toxic dose of caffeine is about 10g per day, approximately 100 cups of coffee would be required, per day, to produce a toxic effect.
Although that seems impossible, if you are drinking coffee along with other drugs or dietary supplements, total caffeine content may accumulate.
The caffeine content of decaffeinated drinks is very small; approximately 2 to 6mg per 250 ml.
Tea: 26-47mg Per 8oz Cup (1-5 Hours of Wakefulness)
The caffeine content of tea varies but is generally less than an equivalent cup of coffee – per 8oz cup, black tea contains 47mg; chai tea 26mg; green tea 33mg; iced tea 26mg; and even ‘caffeine-free’ herbal tea contains around 12mg .
There are many factors that influence the caffeine content of tea – such as the parts of the plant used, the growing conditions, the type of tea, the fertilizer used, and the brewing method.
The caffeine content of tea is very small, but it also contains other active ingredients, like theophylline, theobromine, and L-theanine that make keep you awake.
The reduced content of caffeine in tea is actually helpful and reduces stress.
Researchers in Japan studied the beneficial effects of green tea and found that it improves sleep quality due to its stress-reducing effect .
Soft Drinks: 30-46mg Per 12oz (1.2-5 Hours of Wakefulness)
The caffeine content of soft drinks is variable but is generally less than other beverages.
The FDA limits the caffeine content of carbonated drinks to 0.02% or 71 mg for a 355ml (12 ounces) beverage.
According to UpToDate Medicine, the caffeine content in a 355ml (12 oz) bottle of Coke is 30mg, Diet Coke has 47mg, Pepsi contains 37 mg, Mountain Dew has 55mg, and 7-Up has none.
As 400mg of caffeine is generally considered safe, a person can consume up to 10 (355ml) cans of Coke without experiencing the significant side effects of caffeine.
However, please remember that soft drinks have many other side effects like weight gain, increased blood pressure, high cholesterol, diabetes, heart attack, and dental problems.
Although the small caffeine content doesn’t cause sleep disturbance, other ingredients like sugar can result in shorter sleep duration and frequent awakening.
According to research, individuals who drink more than three soft drinks per day have a 50% increased chance of having sleep disturbance than those who drink one or fewer drinks per day .
Therefore, a person should avoid drinking soft drinks in the evening and at night, in order to have a night of good quality sleep.
Energy Drinks: 108-120mg Per 12oz (4-12 Hours of Wakefulness)
Energy drinks are some of the most caffeine-dense drinks that you can consume – per 12oz, Monster has 120mg, Red Bull has 114mg, Full Throttle has 108mg, and Mountain Dew has 54mg; which can potentially keep you awake for between 2 and 12 hours .
Energy drinks can cause significant sleep disturbance due to multiple factors, including CNS stimulation, diuresis, increased blood pressure, and dehydration .
According to a study published by the CDC, those individuals who take three or more energy drinks per day usually sleep less than 4 hours a night.
I do not recommend taking energy drinks in the evening or at night.
The best recommendation is to take energy drinks at least 6 to 8 hours before sleep .
How Caffeine Affects Your Body
Below is an explanation as to how caffeine affects your body:
Caffeine Enters the System Rapidly After Ingestion
Caffeine is absorbed quickly from the gastrointestinal tract in human beings.
Almost all caffeine (99%) is absorbed within 45 minutes of intake.
Caffeine Performs a Stimulatory Function
Caffeine is a very potent stimulator of the nervous system and keeps the body alert.
Caffeine exerts its effects on many organs; however, the CNS effects are the most important.
The main action of caffeine is the blockage of adenosine receptors.
Adenosine receptors are found in all brain parts which are activated when adenosine attaches to them.
Once activated, they release inhibitory chemicals, resulting in relaxation, fatigue, and increased sleep duration.
The chemical structure of caffeine resembles that of adenosine, which means it can attach to adenosine receptors.
When caffeine occupies these receptors, adenosine cannot mediate its relaxation effects.
Inhibitory chemicals are reduced, while excitatory chemicals predominate in the brain.
This results in alertness, decreased sleep, short reaction time, and increased performance.
These properties of caffeine make it very useful for neurodegenerative diseases like Parkinson’s Disease.
Increases Energy Expenditure
Another function of caffeine is to increase the body’s metabolic rate, which results in increased energy expenditure.
That’s why caffeine-containing beverages, like green tea, are commonly used for weight management, obesity, and diabetes mellitus.
The cardiovascular effects are also important; these include increased heart rate, increased blood pressure, and increased risk of heart disease.
Caffeine is Removed from the System Through the Liver and Kidneys
There are two mechanisms by which caffeine can be removed from the system.
A small amount of caffeine is directly filtered out of the body in the urine, by the kidneys.
The liver metabolizes the rest into its metabolites, including paraxanthine, theobromine, and theophylline, which are excreted in the urine.
Half-life is the time a drug takes in the body to be reduced by 50%.
The half-life of caffeine is about 5-6 hours.
This means that if you take 100 mg of caffeine, then after 5-6 hours, only 50mg will remain in the body.
Please remember that complete removal of the drug takes many half-lives; 4 to 5 half-lives are required to remove 95 to 97% of the drug from the body.
So we can safely say that after 20 to 24 hours, only a small amount of caffeine is left in the body, while a major portion (97%) will have been removed .
Paraxanthine mediates many of the pharmacological effects of caffeine.
So the extent of conversion to Paraxanthine is also a factor that determines the true time caffeine works in the system.
6 Factors Affecting the Duration of Action of Caffeine
Caffeine affects people differently.
Here are 6 factors that can affect how caffeine impacts your system:
The metabolizing of caffeine decreases as we age, and caffeine stays in the system for a longer period.
According to a survey, about 90% of Americans take caffeine daily, consuming an average of 200 mg per day.
We commonly prescribe caffeine to premature neonates, to decrease the risks of apnea and breathing problems.
Some older people also love to consume coffee in the evening, and at night.
But the physiological and metabolic effects of caffeine are different in different age groups.
Older people have increased sensitivity to caffeine, due to low-fat tissue.
Researchers have shown that the blood levels of older people have higher caffeine content than younger people, after receiving the same dose.
Moreover, caffeine stays much longer (about 33%) in the older people’s systems, compared to younger individuals .
2: Genetic Factors
Genetic factors play a very important role in determining the amount of caffeine a person can drink, and the individual’s response to the caffeine.
About 90% of caffeine is metabolized in the liver, coded by a gene called CYP1A2.
Individuals show different thresholds to caffeine’s effects and side effects, due to polymorphism of the CYP1A2.
Individuals with higher CYP1A2 activity are fast metabolizers and can tolerate a large amount of coffee without experiencing any stimulant effects.
Slow metabolizers have low enzyme activity and are sensitive to even a small amount of caffeine .
These individuals are more susceptible to anxiety, panic attacks, increased blood pressure, sleep disturbance, and insomnia.
The activity of CYP1A2 is also affected by many factors, such as smoking, drug use, and dietary factors.
Most of the effects of caffeine are produced by its actions on the adenosine and dopamine receptors.
Research has shown that many genetic variations exist in the number and activity of these receptors.
Polymorphism in the receptors is also one of the causes of the difference in sensitivity to caffeine intake .
3: Caffeine Tolerance
The stimulant effects of caffeine are reduced with the continued use of caffeine.
Caffeine works by blocking the adenosine receptors in the brain and increasing the concentration of excitatory neurotransmitters.
When caffeine is consumed regularly over time, the body responds by increasing the number of adenosine receptors.
Therefore, it becomes more difficult to block the action of adenosine.
An increased dose of caffeine is required to produce the same stimulatory effects.
Smoking increases the metabolizing of caffeine, by increasing the activity of the enzyme xanthine oxidase in the liver.
When smoking is stopped, the metabolization of caffeine returns to the baseline level .
Smoking also influences the activity of the CYP1A2 gene, resulting in increased activity of the enzymes responsible for eliminating caffeine from the system.
However, smoking shares many of the stimulatory effects of caffeine.
So please remember that although smoking increases the clearance of caffeine from the system, it can produce all of these effects by itself.
So individuals who are taking caffeine and nicotine together are at increased risk of developing sleep disturbance, insomnia, hypertension, anxiety, and panic attacks.
5: Contraceptive Use
The use of oral contraceptive pills can double the half-life of caffeine, and increase the length of time it stays in the system.
This is due to decreased excretion of caffeine and its metabolites (especially paraxanthine) from the kidneys .
So a person taking contraceptives and caffeine experiences stimulatory effects for a longer period of time than others.
6: Liver Disease
As most of the metabolization of caffeine takes place in the liver, liver disease will decrease the removal of caffeine from the body.
The liver can be affected by chronic alcohol intake, hepatitis B & C, diabetes, obesity, and drugs.
These factors result in the loss of the liver’s normal function.
This is called Chronic Liver Disease (CLD).
In CLD, the activity of CYP1A2 is compromised, resulting in the decreased metabolization of the caffeine.
Hence, the time for which it stays in the system is prolonged.
Researchers at the Biochemistry Department, Bromley Hospital, Kent, U.K, designed a trial to study this effect.
They divided the subjects into two groups.
One group had chronic liver disease, while the other consisted of healthy individuals.
They gave an equal dose of oral caffeine to both groups and measured the caffeine levels in the blood, and its urinary excretion.
They found out that patients with CLD had decreased excretion of caffeine, and that their serum levels were higher than the others .
4 Ways Caffeine Keeps You Awake
There are many ways by which caffeine exerts its stimulatory effects and keeps you awake.
Four of them are discussed below:
1: Increased Concentration of Excitatory Chemicals in the Brain
Although caffeine can affect almost every organ in the body, its effects on the central nervous system are most pronounced.
The psycho-stimulant actions of caffeine are mediated through the adenosine receptors.
Adenosine receptors (AR) are found abundantly in all parts of the brain.
There are four classes of these receptors: A1, A2A, A2B, and A3.
A1 and A2A are the only receptors that are affected by caffeine.
A2B has a very small affinity for caffeine, while A3 is usually involved with different diseases.
Adenosine binds to these receptors and increases the release of inhibitory neurotransmitters like GABA and serotonin.
It exerts a relaxant and sleep-promoting effect.
Caffeine and paraxanthine look like adenosine to the receptors, because of a similarity in their structure.
Caffeine and its metabolites (like paraxanthine and theophylline) compete with adenosine to bind to target receptors.
When we consume caffeine in small amounts, there isn’t enough caffeine in the brain to block the action of adenosine.
However, when caffeine levels increase in the body, adenosine blockage also increases.
According to researchers, about 4 to 5 cups of coffee, or 450mg of caffeine, are required to block 50% of the adenosine receptors .
When adenosine receptors are blocked, the concentration of excitatory neurotransmitters, like glutamate, acetylcholine, dopamine, and epinephrine increases – while inhibitory chemicals, like dopamine, serotonin, and GABA decrease.
This results in increased alertness, improved cognition, decreased sleepiness, prolonged sleep latency, and increased cerebral perfusion.
When caffeine intake exceeds 400mg per day, it can result in hyperactivity, decreased attention span, jitteriness, and convulsions.
This effect of caffeine is very useful for some diseases, like Parkinson’s and Alzheimer’s disease, in which neurotransmitters are decreased in the body.
Several studies have shown that caffeine can improve motor and non-motor symptoms of Parkinson’s disease, and can be very useful in its management.
The dopamine receptor is another receptor in the brain that is blocked by caffeine, to produce similar stimulant effects.
2: Cardiovascular Effects
Caffeine also has stimulatory effects on the cardiovascular system and results in increased coronary blood flow.
These effects are usually produced when caffeine is used regularly.
They are produced by the inhibition of an enzyme called phosphodiesterase.
Inhibition of this enzyme results in increased catecholamine (adrenaline and nor-epinephrine), which results in a fight or flight response.
Cardiovascular effects of caffeine include increased heart rate, palpitations, and irregular heartbeat.
Caffeine also constricts blood vessels, which results in increased blood pressure.
When a large amount of caffeine is used for a long period, the incidence of heart failure, arrhythmia, and sudden cardiac arrest, increases .
A person with a racing heart rate is more likely to remain awake than a person with normal heart activity.
In my professional opinion, heart patients should avoid using caffeine, as they are more likely to develop these side effects.
3: Increased Production of Urine
Another factor that keeps us awake is the increased production of urine, and the urge to urinate at night.
Coffee consumption is usually considered safe, as it does not increase the risk of chronic kidney disease.
However, caffeine does affect the kidneys in a way that is important for sleep-conscious people.
Caffeine also blocks the adenosine receptors in the kidneys, resulting in increased blood flow to the kidneys.
The secretion of an enzyme called renin is also increased by caffeine consumption.
These effects result in increased urine production, an effect known as diuresis .
When we consume coffee or other caffeine-containing beverages, the diuresis effect is highest at night.
This leads to a disturbed sleep cycle, frequent awakening, and daytime sleepiness.
4: Increased Anxiety and Agitation
Although the stimulatory effects of caffeine are generally useful during the day, this is may not be the case for patients with anxiety disorder.
Caffeine tends to mimic many symptoms of anxiety, such as restlessness, nervousness, racing heart rate, and gastrointestinal problems .
Caffeine consumption worsens the disease if a person already has an anxiety disorder.
Moreover, many of the drugs used for anxiety can negatively interact with caffeine, and make it very difficult for the patient to control the symptoms.
Anxiety results in sleep disturbance, which further worsens the anxiety, and the cycle continues.
5 Ways to Get Caffeine Out of Your System Quickly
Here are 5 ways to get caffeine out of your system faster so that you can get to sleep:
1: Stop Further Ingestion of Caffeine
As the stimulatory effects of caffeine wean off spontaneously from the body after a few hours, the best strategy is to let the body flush the caffeine from its system naturally.
What we can do to help, is to stop consuming more caffeine.
This may seem obvious but should be stressed, as many sources of caffeine are not widely known, and you could unwittingly continue adding new caffeine to your system.
These sources include soft drinks, chocolate, chewing gum, and energy drinks.
Caffeine is also present in some painkillers, flu medicines, and many supplements.
Another recommendation for cutting off caffeine intake is to choose decaffeinated drinks that contain a negligible amount of caffeine but provide the same benefits.
I always tell my patients to taper off their dose of caffeine gradually, to avoid withdrawal symptoms.
When caffeine is used for a long period, the body can become dependent.
Therefore, if caffeine intake is stopped abruptly, you can develop a set of withdrawal symptoms.
These may include headache, fatigue, lethargy, nausea, and difficulty concentrating.
So the best advice is to slowly decrease the amount of caffeine you consume each day, until ultimately withdrawing it completely.
2: Drink Plenty of Water
Some caffeine is removed directly from the liver, while the rest is converted into its metabolites, which are then filtered through the kidneys.
The kidneys’ job is to filter out all the blood, reabsorbing what is useful, and excreting the remaining substances as urine.
Drugs and other chemicals require water for their excretion.
When we drink plenty of water, a large amount of urine is produced, making it easier for the kidneys to flush out caffeine and its metabolites.
Caffeine energizes the body and increases the utilization of water, so you are at increased risk of developing dehydration.
A dehydrated body is more vulnerable to the effects of caffeine.
Therefore, drinking plenty of water will help you stay hydrated.
Research has shown that caffeine consumption increases thirst in people who are not habitual drinkers.
Increased thirst can disrupt your sleep by waking you up at night to satisfy this need.
So drinking a lot of water will prevent sleep disturbance caused by midnight thirst.
3: Eat a Diet Rich in Cruciferous Vegetables
Cruciferous vegetables are a diverse group that belongs to the Brassica family.
Members of this family include cabbage, broccoli, kale, turnips, and Swiss chard.
A diet rich in cruciferous vegetables increases the metabolization of caffeine and helps flush it out of the system.
I have already explained that about 90% of caffeine is broken down into smaller products by special enzymes called CYP1A2.
So the best way to remove caffeine from the system is to increase the activity of these enzymes.
A study conducted at the Fred Hutchinson Cancer Research Center showed that cruciferous vegetables increase the activity of CYP1A2 by 18 to 37%.
This beneficial effect is due to a special compound called glucosinolate; a potent stimulator of this enzyme .
But please note that this doesn’t mean that if you are experiencing side effects of caffeine, you can simply eat a vegetable as an antidote.
These vegetables work at the molecular level, and that takes some time.
On average, vegetables take 6 to 7 days to have maximum effect.
So regular consumption of vegetables is important if you want to avoid the unwanted effects caused by caffeine consumption.
4: L-Theanine Supplementation
Although there is no antidote for caffeine, the only thing that offers a chance of reversing the effects of caffeine is L-theanine.
L-theanine is an amino acid that prevents excitatory neurotransmitters, like glutamate, from binding to its receptors in the brain.
It has a calming effect on the brain and opposes the effects of caffeine on the autonomic system.
It decreases heart rate, blood pressure, vibration, stress, and anxiety .
Nature has added this natural antidote to green tea, but the amount is very low.
5: Practice Relaxation Exercises
Relaxation techniques, like deep breathing exercises, meditation, or yoga are very important for managing the symptoms caused by caffeine intake.
Problems caused by too much caffeine include irregular heart rate, increased breathing, and anxiety.
If you go to bed with these symptoms, it will not be possible to sleep comfortably.
Some people do strenuous exercise, as they feel more energetic, but this can only worsen the problem.
Exercise increases the heart rate, breathing rate, and alertness even further, and it becomes almost impossible to sleep.
The best advice is to calm the body and wait for the effects of the caffeine to wear off.
Deep Breathing Exercises
Deep breathing exercises are very simple and easy to perform.
Sit comfortably on a chair and focus on your breathing.
Take a deep breath through your nose, and hold for five seconds.
Then exhale slowly.
Repeat this cycle for a few minutes.
Yoga is another option that you can try, which may help to reduce the stress and anxiety associated with caffeine consumption.
Caffeine consumption can prevent you from having a night of good quality sleep, by keeping you awake.
The caffeine sensitivity of every individual is different, but you should limit your caffeine intake to less than 400mg per day.
Another measure that you can take to avoid the harmful effects of caffeine is to stay hydrated by drinking plenty of water.
Cruciferous vegetables and L-theanine are helpful in countering the adrenaline rush caused by caffeine.
Deep breathing exercises and yoga are also helpful in calming the body after consuming caffeine.
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No part of this website offers medical advice – always consult with a qualified professional for the best guidance.
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Main image: ‘Teenage Boy Drinking Caffeine Energy Drink Gaming At Home Using Dual Computer Screens At Night’ by monkeybusiness (used with permission and commercially licensed through Envato Elements).
Dan is the founder and head content creator at Bedroom Style Reviews.
He has been working as a professional online product reviewer since 2015 and was inspired to start this website when he ended up sleeping on a memory foam mattress that was too soft and gave him backache.
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Dan is a qualified NVQ Level 2 Fitness Instructor with 6 years’ experience helping clients improve their health through diet, exercise, and proper sleep hygiene.
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