The Surprising Effects of Caffeine on Your Body

Do you feel like you need a cup of coffee or tea in the morning to wake up? Or an energy drink to get you through the afternoon? There’s a good chance you do and you probably know it’s because of the caffeine content but have you ever considered what is going on in your body when you have caffeine?

When it comes to consuming caffeine, it may be all or nothing. Some people rely on their morning java for an energy jolt, while it leaves others feeling jittery and unproductive. Tolerance is highly individualized.

Keep reading to learn more about caffeine’s influence on your body – and what steps you can take to maximize the health benefits of caffeine while also minimizing any risks. 

Did you know?
Caffeine is so widely available these days that around 80% of the world’s population consumes a caffeinated product daily. 90% of adults in North America consume it daily. (15)

Green tea is a great natural source for caffeine and antioxidants. (16)

What is caffeine?

Caffeine is a natural substance found in over 60 different plant species. It’s the most widely used psychoactive substance (drug) on the planet. Caffeine affects how we think and feel, acting as a stimulant to our central nervous systems and our metabolism. (1)

Caffeine is part of a group of drugs known as methylxanthines, which speed up the messages traveling between our brains and our bodies. It fires off more neurons and the release of neurotransmitters, such as dopamine and norepinephrine. Which, in turn, makes you feel energized and more awake. (24)

Natural sources of caffeine

Some examples of common natural sources of caffeine include:  (31)

  • Coffee beans
  • Tea leaves
  • Cacao pods (use to make chocolate products)
  • Kola nuts (used to flavor sodas)
  • Ginseng
  • Yerba Mate 
  • Guarana
  • Taurine (used in Red Bull energy drinks)

Synthetic forms of caffeine

It can also be produced synthetically and put into foods, drinks, and medications. For example, synthetic caffeine is a common ingredient in over-the-counter pain relievers used to help combat the common cold or headache or energy drinks. (31) People can also opt to take synthetic caffeine pills or supplements over a cup of coffee.

Did you know?
Caffeine is also found in some headache and migraine medications.

How different sources of caffeine compare

Keep in mind that the amount of caffeine consumed in beverages varies a lot and is contingent, for example, on the strength of the drink and the amount consumed. For example, if you are drinking coffee, the caffeine strength depends on the type of coffee beans you are ingesting and how they are prepared. (19)(7)

Energy drinks vs. espresso

How does the caffeine in a monster energy drink compare to the caffeine in a shot of espresso? It depends on the strength of the espresso shot. Monster energy comes in a 500 ml can and contains 160mg of caffeine, but just one shot of espresso can range from having 75 mg to over 200 mg of caffeine. (4)(12)

Wondering how much caffeine is in chocolate and other common sources? We’ve put together a little guide below to give you an idea of how different common sources compare.


Coffee (brewed cup) – 8 ounces (237ml) – 95 mg (3)
A shot of espresso – 1 ounce (29.5ml) – 40 mg (3)


Green tea – 8 ounces (237ml) – 35 mg (3)
Lipton black tea – 8 ounces (237ml) – 55 mg (3)
Lipton Iced tea – 8 ounces (237ml) – 50 mg (3)
Herbal Tea – 8 ounces (237ml) – 0mg (3)


Coke – 7.5 ounces (222ml) – 21 mg (3)
Diet coke – 7.5 ounces (22ml) – 28 mg (3)
Pepsi – 12 oz (354 ml) – 37.5 mg (3)
Mountain Dew – 12 oz (354) – 53 mg (3)

Energy Drinks

Monster – 16 oz (500ml) – 173 (3)
NOS – 16 oz (500ml) – 160 (3)
Rockstar – 16 oz (500ml) – 158 (3)
Red Bull – 16 oz (500ml) – 148 (3)
Red bull – 8.4 ounces (248ml) – 77 mg (3)


Excedrin extra strength – 2 tablets – 130mg (3)
NoDoz – 1 tablet – 200 mg (3)
Vivarin – 1 tablet – 200 mg (3)


Chocolate drinks – 8-ounces (237ml) – 2mg to 12 mg (3)
Milk chocolate bar – 1 bar (1.55 oz) 9 mg (3)
Chocolate chips, semi-sweet – 1 cup – 104 mg (3)

A 16fl oz matcha latte has roughly 80mg of caffeine. (19)

Did you know?
When it comes to caffeine in tea vs. coffee popularity, coffee accounts for 54% of caffeine consumption in the world. Tea accounts for another 43%. (27, 32)

How much caffeine do people consume on average?

Globally, the average caffeine intake per individual over the age of 18 is 71mg per day (which is around the amount of caffeine you’d find in one cup of instant coffee). However, individuals in developed countries such as the U.S. or Canada consume a lot more caffeine. (25)

Did you know?
In the U.S., adults consume, on average, 300mg of caffeine per day. (25)

Caffeine metabolism varies from person to person

Some people can just naturally handle more caffeine than others. This is because every individual has a unique caffeine metabolism that is influenced by a variety of factors, such as age, sex and hormones, weight, smoking, diet, medications, and more. (23)

How long does caffeine last?

Caffeine is quickly absorbed in the body when you drink it, entering your bloodstream through the lining of your mouth, esophagus, and stomach.

Most individuals absorb 99% of the caffeine they’ve drunk within forty-five minutes. Then the effects tend to last 1.5-9.5 hours. The speed at which you metabolize caffeine comes down to specific genes. (11) (33)

It’s in your genes

Have you heard of the coffee gene? Scientists have honed in on one specific gene, PDSS2. People with a particular variation of this gene process caffeine more slowly than others, meaning they need less coffee to feel the same stimulating effects. (24)

What are caffeine’s effects on the body?

Caffeine affects your body’s metabolism in several ways. 

  • It stimulates your central nervous system, providing you a jolt of energy and increased alertness. (2)
  • It acts as a diuretic, which means it helps your body get rid of extra salt and water by increasing the urge to urinate. (18)
  • It increases your blood pressure. (21) (13)
  • It may interfere with the absorption of calcium in the body. (14)
  • It can boost the metabolic rate and increase fat burning, but after a while, this effect diminishes as the body becomes tolerant in long-term caffeine users. (30) (6)

Did you know?
If you are looking to maximize caffeine for fat burning, experts recommend changing up your caffeine intake to prevent a buildup of tolerance. Try two weeks on and two weeks off. (17)

What are the signs of too much caffeine?

For some people, it can be harmful to consume up to or more than 400 mg of caffeine a day. If you drink or ingest too much caffeine, you may notice health problems such as: (34) (29)

  • Restlessness 
  • Jitters
  • Diarrhea
  • Insomnia
  • Caffeine headaches
  • Dizziness
  • Rapid or abnormal heart rhythm
  • Dehydration
  • Muscle tremors
  • Eye-twitch
  • Anxiety
  • Dependency, meaning you need more to get the same results. 

Ideally, it’s best to limit intake to around 150-200 mg a day to reduce your risk of any of the side effects listed above if you are sensitive to caffeine (10)

Did you know? 
To avoid adverse caffeine side effects, try drinking no more than two 8-ounce cups of coffee or 5 cups of 8-ounce green tea a day. (10)

Who should avoid or limit their caffeine intake?

There are specific individuals, as we mentioned above, that have a naturally lower tolerance for caffeine. You should take extra precautions and check in with your practitioner about limiting or avoiding caffeine if you: (23) (26)

  • Are currently pregnant
  • Are breastfeeding
  • Have sleep disorders, such as insomnia
  • Suffer from migraines or other chronic headaches
  • Have high blood pressure
  • Are under the age of 18
  • Have fast or irregular heart rhythms
  • Have anxiety 
  • Have GERD or ulcers
  • Someone currently taking certain medications or supplements that act as stimulants

Did you know?
Caffeine pregnancies have been linked to low-birth-weight babies and that drinking coffee is linked to a longer pregnancy. (9)

What are caffeine withdrawal symptoms?

If you have been consuming caffeine regularly and then just suddenly stop, there’s a good chance you experience caffeine withdrawal symptoms. Symptoms usually begin within 12-24 hours of the last dose of caffeine and can persist for 24-48 hours. Symptoms may include: (28)

  • Headaches
  • Irritability
  • Drowsiness
  • Difficulty concentrating
  • Nausea
  • Low energy levels
  • Vomiting

When it comes to caffeine and sleep, it’s often not the best combination. One study found that caffeine delays the time of your body clock. (5)

Did you know?
In heavy caffeine consumers, withdrawal symptoms can occur within six hours, and symptoms may last for a more extended period. (20)

The bottom line – moderation is key

When it comes to caffeine, every individual is different, and moderation is key. Try and opt for natural sources of caffeine in moderation, such as coffee, green tea, and yerba mate over sugary sodas and lattes.

Aim to maximize the potential health benefits without the added side effects and caffeine health risks by keeping the following in mind: 

  • If you tolerate caffeine well, you should limit your caffeine consumption to no more than about 300 mg to 400 mg per day. In layman’s terms, this is about three to four cups (8-oz) of coffee. If you are very sensitive, try and keep it to 100 to 200 mg per day.
  • Try and avoid caffeine in the late afternoon and evening to prevent trouble sleeping.
  • Pregnant women and individuals with heart problems and high blood pressure should avoid high levels of caffeine.
  • Parents should limit the amount of caffeine that their children consume in soda, chocolate, and teas.

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  1. Evans, J., Richards, J., & Battisti, A. (2019). Caffeine. Retrieved from
  2. Acheson, K. J., Zahorska-Markiewicz, B., Pittet, P., Anantharaman, K., & Jéquier, E. (1980). Caffeine and coffee: their influence on metabolic rate and substrate utilization in normal weight and obese individuals. The American Journal of Clinical Nutrition, 33(5), 989–997.
  3. Ahluwalia, N., & Herrick, K. (2015). Caffeine Intake from Food and Beverage Sources and Trends among Children and Adolescents in the United States: Review of National Quantitative Studies from 1999 to 2011. Advances in Nutrition, 6(1), 102–111.
  4. Bailey, R. L., Saldanha, L. G., Gahche, J. J., & Dwyer, J. T. (2014). Estimating caffeine intake from energy drinks and dietary supplements in the United States. Nutrition Reviews, 72, 9–13.
  5. Burke, T. M., Markwald, R. R., McHill, A. W., Chinoy, E. D., Snider, J. A., Bessman, S. C., … Wright, K. P., Jr. . (2015). Effects of caffeine on the human circadian clock in vivo and in vitro. Science Translational Medicine, 7(305).
  6. Campbell, B. I., Colquhoun, R. J., Zito, G., Martinez, N., Kendall, K., Buchanan, L., … Cloer, B. (2016). The effects of a fat loss supplement on resting metabolic rate and hemodynamic variables in resistance trained males: a randomized, double-blind, placebo-controlled, cross-over trial. Journal of the International Society of Sports Nutrition, 13(1).
  7. Cappelletti, S., Daria, P., Sani, G., & Aromatario, M. (2015). Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drug? Current Neuropharmacology, 13(1), 71–88.×13666141210215655
  8. Chacko, S. M., Thambi, P. T., Kuttan, R., & Nishigaki, I. (2010). Beneficial effects of green tea: A literature review. Chinese Medicine, 5(1), 13.
  9. Chen, L.-W., Wu, Y., Neelakantan, N., Chong, M. F.-F., Pan, A., & van Dam, R. M. (2014). Maternal caffeine intake during pregnancy is associated with risk of low birth weight: a systematic review and dose-response meta-analysis. BMC Medicine, 12(1).
  10. C.O.M.N., Board, F. A. N., & Institute of Medicine. (2001a). 4: Safety of Caffeine Usage. In  Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations. Retrieved from
  11. C.O.M.N., Board, F. A. N., & Institute of Medicine. (2001b). 2. Pharmacology of Caffeine. Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations. Amsterdam, Netherlands: Amsterdam University Press.
  12. Derossi, A., Ricci, I., Caporizzi, R., Fiore, A., & Severini, C. (2018). How grinding level and brewing method (Espresso, American, Turkish) could affect the antioxidant activity and bioactive compounds in a coffee cup. Journal of the Science of Food and Agriculture.
  13. Hartley, T. R., Sung, B. H., Pincomb, G. A., Whitsett, T. L., Wilson, M. F., & Lovallo, W. R. (2000). Hypertension Risk Status and Effect of Caffeine on Blood Pressure. Hypertension, 36(1), 137–141.
  14. Heaney, R. P. (2002). Effects of caffeine on bone and the calcium economy. Food and Chemical Toxicology, 40(9), 1263–1270.
  15. Heckman, M. A., Weil, J., & de Mejia, E. G. (2010). Caffeine (1, 3, 7-trimethylxanthine) in Foods: A Comprehensive Review on Consumption, Functionality, Safety, and Regulatory Matters. Journal of Food Science, 75(3), R77–R87.
  16. Iso, H., Date, C., Wakai, K., Fukui, M., & Tamakoshi, A. (2006). The Relationship between Green Tea and Total Caffeine Intake and Risk for Self-Reported Type 2 Diabetes among Japanese Adults. Annals of Internal Medicine, 144(8), 554.
  17. Lara, B., Ruiz-Moreno, C., Salinero, J. J., & Del Coso, J. (2019). Time course of tolerance to the performance benefits of caffeine. PLOS ONE, 14(1), e0210275.
  18. Maughan, R. J., & Griffin, J. (2003). Caffeine ingestion and fluid balance: a review. Journal of Human Nutrition and Dietetics, 16(6), 411–420.
  19. McCusker, R. R., Goldberger, B. A., & Cone, E. J. (2006). Caffeine Content of Energy Drinks, Carbonated Sodas, and Other Beverages. Journal of Analytical Toxicology, 30(2), 112–114.
  20. Meredith, S. E., Juliano, L. M., Hughes, J. R., & Griffiths, R. R. (2013). Caffeine Use Disorder: A Comprehensive Review and Research Agenda. Journal of Caffeine Research, 3(3), 114–130.
  21. Mesas, A. E., Leon-Muñoz, L. M., Rodriguez-Artalejo, F., & Lopez-Garcia, E. (2011). The effect of coffee on blood pressure and cardiovascular disease in hypertensive individuals: a systematic review and meta-analysis. The American Journal of Clinical Nutrition, 94(4), 1113–1126.
  22. National Center for Biotechnology Information. PubChem Database. Caffeine, CID=2519, (accessed on Feb. 25, 2020)
  23. Nehlig, A. (2018). Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption. Pharmacological Reviews, 70(2), 384–411.
  24. PDSS2 decaprenyl diphosphate synthase subunit 2 [Homo sapiens (human)] – Gene – NCBI. (2019, December 20). Retrieved February 25, 2020, from
  25. Pitchumoni, C. S., & Dharmarajan, T. (2012). Geriatric Gastroenterology. In Geriatric Gastroenterology (2012th ed., pp. 92–93). Retrieved from,+the+average+caffeine+intake+per+individual+70+mg+per+day&source=bl&ots=AOmTHY0jsU&sig=ACfU3U29QwH78nyL9YGAaCdLop1IudTgog&hl=en&sa=X&ved=2ahUKEwjW2pXah-XmAhVMh-AKHWLrCMcQ6AEwCXoECAgQAg#v=onepage&q=Globally%2C%20the%20average%20caffeine%20intake%20per%20individual%2070%20mg%20per%20day&f=false
  26. Reyes, C., & Cornelis, M. (2018). Caffeine in the Diet: Country-Level Consumption and Guidelines. Nutrients, 10(11), 1772.
  27. Shahbandeh , M. (2019). Production of tea worldwide. Retrieved from
  28. Sigmon, S. C., Herning, R. I., Better, W., Cadet, J. L., & Griffiths, R. R. (2009b). Caffeine withdrawal, acute effects, tolerance, and absence of net beneficial effects of chronic administration: cerebral blood flow velocity, quantitative EEG, and subjective effects. Psychopharmacology, 204(4), 573–585.
  29. Smith, A. (2002). Effects of caffeine on human behavior. Food and Chemical Toxicology, 40(9), 1243–1255.
  30. Tabrizi, R., Saneei, P., Lankarani, K. B., Akbari, M., Kolahdooz, F., Esmaillzadeh, A., … Asemi, Z. (2018). The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials. Critical Reviews in Food Science and Nutrition, 59(16), 2688–2696.
  31. Temple, J. L., Bernard, C., Lipshultz, S. E., Czachor, J. D., Westphal, J. A., & Mestre, M. A. (2017). The Safety of Ingested Caffeine: A Comprehensive Review. Frontiers in Psychiatry, 8.
  32. Weinberg, B. A., & Bealer, B. K. (2000). The World of Caffeine: The Science and Culture of the World’s Most Popular Drug (1st ed.). Retrieved from,+coffee+accounts+for+54%25+of+caffeine+consumption+in+the+world.+Tea+accounts+for+another+43%25.&source=bl&ots=TXhmtnZnmd&sig=ACfU3U0fNT9oVFouxwk0HcmBYj_Gwb1UJA&hl=en&sa=X&ved=2ahUKEwiH1qymh-XmAhVjiOAKHeLBBtkQ6AEwCXoECAkQAg#v=onepage&q=When%20it%20comes%20to%20caffeine%20in%20tea%20vs.%20coffee%20popularity%2C%20coffee%20accounts%20for%2054%25%20of%20caffeine%20consumption%20in%20the%20world.%20Tea%20accounts%20for%20another%2043%25.&f=false
  33. White, J. R., Jr, Padowski, J. M., Zhong, Y., Chen, G., Luo, S., Lazarus, P., … McPherson, S. (2016). Pharmacokinetic analysis and comparison of caffeine administered rapidly or slowly in coffee chilled or hot versus chilled energy drink in healthy young adults. Clinical Toxicology, 54(4), 308–312.
  34. Willson, C. (2018). The clinical toxicology of caffeine: A review and case study. Toxicology Reports, 5, 1140–1152.