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Caffeine (An Overview)

Updated: Aug 15, 2023

Evidence-Based. Scientifically Reviewed by Michael Sharpe, MSc.

Caffeine is one of, if not, the most used natural stimulatory supplement. It is often talked about as the dangerous chemical found in energy drinks that can cause serious adverse effects. However, caffeine is being revealed to have many positive health benefits.

In this article, I'll discuss everything you need to know about caffeine.

caffeine spelled with coffee beans

What Is Caffeine?

Caffeine is a naturally occurring stimulant that is present in tea, coffee, and cocoa plants. It works by activating the brain and central nervous system, which keeps you awake and prevents fatigue.

It can also help you increase your physical strength and endurance. However, it is categorised as a nootropic since it primarily stimulates the brain.

Caffeine is derived from coffee beans, although it may also be synthetically manufactured in a laboratory. Whether it's in coffee, energy drinks, tea, or in supplement form, etc, it all has the same chemical structure.

Historians trace the origins of brewed tea back to 2737 B.C. (1)

Many years later, an Ethiopian shepherd is said to have found coffee after seeing how much more vitality it provided his goats.

Caffeinated drinks first appeared on the market in the late 1800s. Caffeinated products are consumed by 80% of the world's population every day, for some parts of the world it is even higher, in some places reaching as high as 90%. (1)

How It Works

Caffeine's primary method is to block adenosine receptors. When adenosine binds to its receptors in the brain, it induces drowsiness and relaxation.

Caffeine inhibits this effect and promotes alertness and wakefulness. (2)

The dopamine, serotonin, acetylcholine, and adrenaline systems are all affected by caffeines effect on the adenosine system.

Caffeine may also raise blood adrenaline levels and enhance dopamine and norepinephrine neurotransmitter activity in the brain. (3)

Caffeine takes effect very quickly. For example, the quantity of caffeine contained in one cup of coffee may enter the bloodstream in as little as 20 minutes and take up to an hour to achieve maximum efficacy. (1)

However, tolerance to caffeine develops with repeated usage. This implies that the benefits of caffeine will be reduced, and a user's sole advantage will be the anti-sleep impact of caffeine. Simply taking more caffeine will not be able to overcome this tolerance.

A tolerance to caffeine may be reduced by lowering or eliminating caffeine intake for a month.


Caffeine has a variety of health and fitness benefits, such as the following.

Enhances Exercise Performance

Caffeine may enhance the utilisation of fat as a source of energy during exercise.

This is advantageous because it increases the energy available to your muscles, possibly prolonging the time it takes your muscles to fatigue. (4)

It may also help with muscular contractions and fatigue tolerance. (1)

When taken 1 hour before exercise, dosages of 2.3 mg/lb of body weight enhanced endurance performance by up to 5%. (5)

Furthermore, studies show that team sports, high-intensity workouts, and resistance exercises all have comparable advantages. (6, 7)

Doses as little as 1.4 mg/lb of body weight are enough to enjoy the advantages. (6)

Finally, it has been shown to decrease perceived effort during exercise by up to 5.6%, making sessions seem more manageable. (8)

With dosages of caffeine above 5 mg/kg, there seems to be a consistent and substantial increase in power output (strength) on both weight lifting and cycle ergometer measures, in both trained and inactive people, provided the individual is not caffeine tolerant.

Caffeine tolerance, or smaller dosages, are less effective at improving strength.

In moderately trained males, power output falls in the morning compared to the afternoon.

Caffeine intake at 3 mg/kg of bodyweight was able to reverse the decrease in power in the AM compared to training in the PM, and equalise performance in both. (23)

Increases Metabolism & Fat Burning

Caffeine may boost metabolism by up to 11% and fat burning by up to 13% due to its capacity to activate the central nervous system. (9, 10, 11)

In practise, taking 300 mg of caffeine per day may help you burn an additional 79 calories each day. (12)

This amount of calories may seem little, but over 1 week those 79 calories each day is an extra ~550 calories burnt off, just by consuming caffeine. (13)

One study on caffeine and weight gain, on the other hand, found that those who drank the most coffee were just 0.8-1.1 lbs (0.4-0.5 kg) lighter at the end. (14)

Improves Mood & Brain Function

Caffeine has the capacity to inhibit the chemical adenosine. Other signalling molecules like as dopamine and norepinephrine are also increased. This shift in brain signalling is believed to improve your mood and cognitive abilities. (15, 16)

Participants exhibited increased alertness, short-term memory, and reaction time after ingesting 37.5-450 mg of caffeine, according to one study. (1)

In addition, one study found that consuming 2-3 cups of caffeinated coffee per day (equivalent to 200-300 mg caffeine) reduced the risk of suicide by 45%. (17)

Another study found that caffeine drinkers had a 13% reduced risk of depression. (18)

However, more caffeine isn't always better when it comes to mood. Some research showed that unless a second cup of coffee was drunk at least 8 hours following the first cup, there were no further advantages. (19)

Drinking 3-5 cups of coffee or more than 3 cups of tea each day may lower your risk of brain disorders like Alzheimer's and Parkinson's by 28-60%. (20, 21, 22)

It's worth noting that, in addition to caffeine, coffee and tea include additional bioactive chemicals that may have other biological roles.

Protects Against Heart Disease & Diabetes

Contrary to popular belief, caffeine does not increase the risk of heart disease. (24, 25, 26)

In reality, studies indicate that men and women who consume 1-4 cups of coffee each day (100-400 mg of caffeine) had a 16-18% reduced risk of heart disease. (27)

Other research has connected consuming 2-4 cups of coffee or green tea per day to a 14-20% reduced risk of stroke. (28, 29)

However, caffeine may increase blood pressure in some individuals. Though, this impact is usually minor (3-4 mmHg) and decreases with time for most people who drink coffee on a daily basis. (30, 31)

Caffeine consumption may also help to prevent diabetes. According to one study, those who consume the most coffee had a 29% reduced risk of type 2 diabetes. Similarly, individuals who consumed the most caffeine had a 30% reduced risk. (32)

The scientists discovered that every 200 mg of caffeine consumed reduces the risk by 12-14%. (32)

Decaffeinated coffee consumption was also related to a 21% reduced incidence of diabetes. This suggests that other compounds within coffee may also help to prevent type 2 diabetes. (32)

Other Benefits

The consumption of coffee has been linked to the following health benefits.

  • Liver Health: Coffee has been shown to lower the risk of liver damage (cirrhosis) by up to 84%. It has the potential to delay disease progression, enhance therapy response, and reduce the risk of mortality. (35)

  • Digestive Health: For as little as three weeks, drinking 3 cups of coffee a day may boost the quantity and activity of good gut bacteria. (36)

  • Longevity: Coffee consumption may reduce the risk of early mortality by up to 30%, particularly in women and individuals with diabetes. (37)

  • Reduced Liver & Colon Cancer Risk: Drinking 2-4 cups of coffee each day may lower the risk of colorectal cancer by up to 38% and liver cancer by up to 64%. (38, 39, 40)

  • Reduced Skin Cancer Risk: Drinking 4 cups of coffee per day may reduce the risk of skin cancer by 20%. (41)

  • Reduced Risk of MS: Coffee users may have a reduced chance of getting multiple sclerosis by up to 30%. However, the research on this matter is mixed. (42, 42)

Sources of Caffeine

Caffeine may be found in the seeds, nuts, and leaves of a variety of plants. Caffeinated foods and drinks are made from these natural sources, which are collected and processed.

The caffeine content per 8-ounce (240 ml) portion of various popular drinks is as follows. (1)

  • Espresso: 240-720 mg

  • Coffee: 102-200 mg

  • Energy Drinks: 50-160 mg

  • Brewed Tea: 40-120 mg

  • Soft Drinks: 20-40 mg

  • Decaffeinated Coffee: 3-12 mg

Caffeine is also found in certain foods. For example; 28 grams of milk chocolate contains 1-15 mg, whereas 28 grams of dark chocolate contains 5-35 mg.

It is also found in several medications such as cold, allergy, and pain relievers.

Many different supplements contain caffeine included in their formula, such as weight loss and pre-workout supplements.

Adverse Effects & Safety

Caffeine can cause the following adverse effects. (33)

  • Insomnia

  • Nervousness

  • Restlessness

  • Stomach discomfort

  • Nausea

  • Increased heart rate and respiration

Higher dosages might cause headaches, anxiety, agitation, and chest pains. Very high dosages can cause an irregular heart beat and possibly even lead to a heart attack. (33)

It is suggested to limit your daily intake of caffeine to 400mg per day, this appears to be the safe level for most healthy adults. (34)

Caffeine, when taken in high quantities during pregnancy, may raise the risk of miscarriage and other complications. Caffeine may also transfer into breast milk, therefore nursing women should keep a careful eye on their caffeine consumption to ensure it is kept to a minimum.

Women who breastfeed and consume a lot of caffeine may cause sleep problems, irritability, and increased bowel movement in their babies.

Therefore, women who are pregnant or breastfeeding should avoid excess caffeine consumption (keep caffeine intake below 200-300 mg per day).


Caffeine has a wide range of interactions with medications and diseases, as listed below.


Below is a list of medications that caffeine interacts with, segregated in three groups, severe (don't take this combination), moderate (avoid this combination if possible or be very careful), and minor (know a possible interaction exists and be careful) interactions.


Other stimulants such as ephedrine.

  • Adenosine

  • Quinolone antibiotics

  • Cimetidine (Tagamet)

  • Clozapine (Clozaril)

  • Dipyridamole (Persantine)

  • Disulfiram (Antabuse)

  • Lithium

  • Oestrogen

  • Fluvoxamine (Luvox)

  • Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

  • Medications for depression (MAOIs)

  • Phenylpropanolamine

  • Pentobarbital (Nembutal)

  • Riluzole (Rilutek)

  • Theophylline

  • Verapamil (Calan, Covera, Isoptin, Verelan)

  • Alcohol

  • Birth control pills (Contraceptive drugs)

  • Fluconazole (Diflucan)

  • Medications for diabetes (Antidiabetes drugs)

  • Mexiletine (Mexitil)

  • Terbinafine (Lamisil)


Below is a list of diseases and conditions that caffeine can make worse, if you have any of these diseases or disorders, caffeine should be taken with caution or avoided.

  • Mental & Brain Disorders: Caffeine may exacerbate mental health issues associated with bipolar, anxiety, and schizophrenia disorders. It may also make symptoms of epilepsy and Parkinson's disease worse.

  • Heart, Blood Pressure & Bleeding: Excess caffeine intake should be avoided by people with heart, blood pressure, and bleeding disorders.

  • Bladder & Bowel: Caffeine can increase bladder and bowel movements.

  • Glaucoma: Caffeine may make symptoms of glaucoma worse.

  • Diabetes: Not enough research on caffeines safety with diabetes is available, use with caution or avoid caffeine if you have diabetes.


Caffeine doses should be customised for each person. Start with around 100 mg if you're new to caffeine supplements. If you've never consumed caffeine before (such as tea and coffee), take even less.

  • Caffeine supplementation for fat-burning is typically 200 mg.

  • Acute strength gains occur at larger dosages, around 500 mg.

  • A dose range of 4-6 mg/kg bodyweight is often used in studies.

Caffeine may be obtained through a variety of sources, including coffee, tea, and energy drinks, but it can also be taken as a pill or a powder.

Many of the effects of caffeine, such as fat burning, strength advantages, and euphoria, are susceptible to tolerance and may not occur in individuals who are accustomed to it, regardless of the dosage.

If you're not sure what dosage to take, stick to around 200 mg. The safe upper suggested limit of caffeine is around 400mg.

More Information

Below is more technical information about caffeine, such as other names, functions and roles, synergies, etc.

Other Names: Coffee extract, Tea extract, 1, 3, 7-Trimethylxanthine

Primary Role: Energy and stimulation

Other Roles: Cognitive and brain health, fat loss, muscle gain, exercise performance

Synergies: Xanthine Oxidase inhibitors like Milk thistle, Curcumin and Quercetin may increase circulating caffeine levels. L-theanine and caffeine increases focus and cognition. Ephedrine and Aspirin in the ECA stack improves fat loss.

Confused With: Caffeic acid

Things to Note

  • Caffeine is a powerful stimulant.

  • Caffeine's metabolic effects differ depending on whether a person is an infrequent user or is a habitual user and is accustomed to caffeine.

  • Some pharmaceutical drugs, such as Fluvoxamine and aromatase inhibitors like Anastrozole, may alter caffeine levels.

  • Genetics, particularly polymorphism in the CYP1A1/2 enzyme, may have an impact on caffeines effect.

  • A 10mg/kg bodyweight dosage in rats is approximately bioequivalent to 250mg in a 70kg person, according to one study, which looked at the variations in metabolism between humans and rats.


  • Caffeine is a stimulant with a systemic vasoconstrictor effect. If you're not accustomed to consuming caffeine or have high blood pressure, you should proceed with caution.

  • Caffeine should not be taken as a supplement in those who have heart problems without first seeing their doctor.

  • Caffeine may also affect the quality of one's sleep; although you may be able to fall asleep, the sleep will be of poor quality.


This section contains links to research, studies, and sources of information for this article, as well as authors, contributors, etc. All sources, along with the article and facts, are subjected to a series of quality, reliability, and relevance checks.

Real Muscle primarily uses high-quality sources, such as peer-reviewed publications, to back up the information in our articles. To understand more about how we fact-check and keep our information accurate, dependable, and trustworthy, read more about us.

This evidence based overview of caffeine features 43 references, listed below.

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5. Hodgson AB, Randell RK, Jeukendrup AE. The metabolic and performance effects of caffeine compared to coffee during endurance exercise. PLoS One. (2013) (Randomised Controlled Trial) ✔

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11. Acheson KJ, Gremaud G, Meirim I, Montigon F, Krebs Y, Fay LB, Gay LJ, Schneiter P, Schindler C, Tappy L. Metabolic effects of caffeine in humans: lipid oxidation or futile cycling? Am J Clin Nutr. (2004, Jan) (Clinical Trial) ✔

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14. Lopez-Garcia E, van Dam RM, Rajpathak S, Willett WC, Manson JE, Hu FB. Changes in caffeine intake and long-term weight change in men and women. Am J Clin Nutr. (2006, Mar)

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17. Michel Lucas, Eilis J. O’Reilly, An Pan, Fariba Mirzaei, Walter C. Willett, Olivia I. Okereke & Alberto Ascherio. Coffee, caffeine, and risk of completed suicide: Results from three prospective cohorts of American adults. The World Journal of Biological Psychiatry. (2014)

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20. Flaten V, Laurent C, Coelho JE, Sandau U, Batalha VL, Burnouf S, Hamdane M, Humez S, Boison D, Lopes LV, Buée L, Blum D. From epidemiology to pathophysiology: what about caffeine in Alzheimer's disease? Biochem Soc Trans. (2014, Apr)

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34. MayoClinic. Caffeine: How much is too much? Healthy Lifestyle. ✔

35. Sammy Saab, Divya Mallam, Gerald A. Cox II, Myron J. Tong. Impact of coffee on liver diseases: a systematic review. Liver int. (2014)

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37. Lopez-Garcia E, van Dam RM, Li TY, Rodriguez-Artalejo F, Hu FB. The relationship of coffee consumption with mortality. Ann Intern Med. (2008, Jun 17)

38. Sang, LX., Chang, B., Li, XH. et al. Consumption of coffee associated with reduced risk of liver cancer: a meta-analysis. BMC Gastroenterol. (2013)

39. Sinha R, Cross AJ, Daniel CR, Graubard BI, Wu JW, Hollenbeck AR, Gunter MJ, Park Y, Freedman ND. Caffeinated and decaffeinated coffee and tea intakes and risk of colorectal cancer in a large prospective study. Am J Clin Nutr. (2012, Aug) ✔

40. Li G, Ma D, Zhang Y, Zheng W, Wang P. Coffee consumption and risk of colorectal cancer: a meta-analysis of observational studies. Public Health Nutr. (2013, Feb) (Meta-Analysis)

41. Loftfield E, Freedman ND, Graubard BI, Hollenbeck AR, Shebl FM, Mayne ST, Sinha R. Coffee drinking and cutaneous melanoma risk in the NIH-AARP diet and health study. J Natl Cancer Inst. (2015, Jan 20)

42. Massa J, O'Reilly EJ, Munger KL, Ascherio A. Caffeine and alcohol intakes have no association with risk of multiple sclerosis. Mult Scler. (2013, Jan)

43. Hedström AK, Mowry EM, Gianfrancesco MA, et al. High consumption of coffee is associated with decreased multiple sclerosis risk; results from two independent studies. Journal of Neurology, Neurosurgery & Psychiatry. (2016) ✔

Citations with a tick indicate the information is from a trusted source.


The information provided in this article is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the guidance of a physician or other competent professional before following advice or taking any supplement. See our terms and conditions.

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