Take Home Points:

  • Caffeine is the most widely used psychoactive substance in the world.

  • Caffeine has been shown to enhance performance on tasks of sustained attention as well as working memory.


  • Caffeine


  • Tea, coffee beans, cocoa products, energy drinks

  • Throughout the world, 70-76 mg/person/day of caffeine are consumed. This number grows to 210-238 mg/person/day in the USA, 400 mg/person/day in Sweden and Finland.1


  • 1,3,7-trimethylxanthine

caffeine_structure Figure 1. Chemical structure of caffeine (1,3,7-trimethylxanthine).

How to Take

  • Take caffeine in a dosage of 100-200mg at a time.

  • Caffeine can be taken alone or as part of a stack, such as the caffeine + theanine combination.

Effects on the Brain

Effects on the brain are outlined below.


  • Caffeine use typically improves attention, as supported by a large number of studies involving dosage amounts ranging from as little as 60 mg to over 200 mg.

  • Caffeine is well-established as an agent to increase alertness. This effect is particularly noticieable in low arousal situations (after benzodiazepine administration, early in the morning, working at night, during illnesses, and in sleep deprivation conditions.2,3,4,5.

  • A 60 mg dose of caffeine yielded significantly improved sustained attention in 45-minute tests in 82 low or non-caffeine-consuming, healthy male (n=41) and female (n=41) adults. Tests used included the Rapid Visual Information Processing Test, attention switch test, and adaptive tracking test.6

  • Low doses of caffeine (75 mg and 150 mg) improved attention in healthy, normal individuals during optimal working conditions.7


  • In a study of 70 participants, those who took caffeine 8 days after withdrawal exhibited improved simple reaction time, and detected targets faster in a cognitive vigilance task.8

  • In a study involving 48 participants, it was found that caffeine (250 mg) increased self-rated alertness, but also increased jitteriness and blood pressure. However, the addition of theanine (200 mg) to the mix counteracted the rise in blood pressure.9

  • A review published in 2013 showed that caffeine has clear beneficial effects on both simple and complex attention tasks.10

  • Furthermore, work has shown that even in the most intense conditions experienced by Navy Seals, a 200 mg dose of caffeine can improve vigilance, reaction time, and alertness, with minimal effects on fine motor functions (as measured by performance on marksmanship).11


  • A dose of 100mg caffeine improved self-reported scores of wakefulness, energy, and clarity of mind in a study involving 60 healthy volunteers.12

  • 75 mg and 150 mg dosages of caffeine significantly improved self-reported scores of clearheadedness, happiness and calmness, ans significantly decreased self-reported tenseness in healthy volunteers.7

Side Effects

  • Excessive use can potentially lead to nausea, diarrhea, cramping, bloating.13

  • A 2002 review concluded that "the literature suggests that extremely high doses of caffeine may increase anxiety, but that this is rarely seen within the normal range of ingestive behavior."14

  • Large doses of caffeine late in the night will increase the time it takes for some people to fall asleep. The effects of smaller doses varies; however, there isn't enough evidence to suggest that health is negatively influenced by caffeine-induced sleep disruptions.14

  • Note that long-term evening/nighttime caffeine use can delay your circadian rhythm - pushing your internal clock to a later bedtime.15

Effects on the Body

Exercise Performance

  • in various scientific studies, caffeine consumption has led to increased anaerobic running capacity, increased power output, and improved performance on aerobic exercise.

  • caffeine improves reaction time in physical tasks

Physiological Parameters

  • caffeine generally increases blood pressure and heart rate

  • caffeine generally is linked to increased testosterone levels after consumption

  • caffeine generally is linked to increased fat oxidation (i.e., fatty acid turnover)

  • chronic caffeine intake generally leads to improved insulin sensitivity16


Approved as a dietary supplement component under provisions of the Dietary Supplement Health and Education Act of 1994.

Check out this caffeine calculator at caffeine informer to get an estimate of the amount of caffeine safe to consume based on your weight. See table 2 for an estimate of the caffeine content in common foods and drinks.

caffeine_content_food_drink Table 2. Caffeine content of select foods and drinks.

Effects on Disease States

  • None listed.

Caffeine & L-theanine

Caffeine and L-theanine can act synergistically to improve alertness and attention. L-theanine can also potentially reverse some of the less favorable physiological effects of caffeine - including increased blood pressure, and reduced flow of oxygenated blood to the head. (Learn more)

  1. Fredholm, B. B., Battig, K., Holmen, J., Nehlig, A., & Zvartau, E. E. (1999). Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol Rev, 51(1), 83-133. Retrieved from

  2. Johnson, L. C., Spinweber, C. L., & Gomez, S. A. (1990). Benzodiazepines and caffeine: effect on daytime sleepiness, performance, and mood. Psychopharmacology (Berl), 101(2), 160-167.

  3. Smith, A., Kendrick, A., Maben, A., & Salmon, J. (1994). Effects of breakfast and caffeine on cognitive performance, mood and cardiovascular functioning. Appetite, 22(1), 39-55. doi:10.1006/appe.1994.1004

  4. Smith, A. P., Kendrick, A. M., & Maben, A. L. (1992). Effects of breakfast and caffeine on performance and mood in the late morning and after lunch. Neuropsychobiology, 26(4), 198-204. doi:118920

  5. Smith, B. D., Davidson, R. A., & Green, R. L. (1993). Effects of caffeine and gender on physiology and performance: further tests of a biobehavioral model. Physiol Behav, 54(3), 415-422.

  6. Wilhelmus, M. M., Hay, J. L., Zuiker, R. G., Okkerse, P., Perdrieu, C., Sauser, J., ... & Silber, B. Y. (2016). Effects of a single, oral 60 mg caffeine dose on attention in healthy adult subjects. Journal of Psychopharmacology, 0269881116668593.

  7. Warburton, D. M. (1995). Effects of caffeine on cognition and mood without caffeine abstinence. Psychopharmacology (Berl), 119(1), 66-70.

  8. Smith, A. P., Christopher, G., & Sutherland, D. (2013). Acute effects of caffeine on attention: a comparison of non-consumers and withdrawn consumers. J Psychopharmacol, 27(1), 77-83. doi:10.1177/0269881112460112

  9. Rogers, P. J., Smith, J. E., Heatherley, S. V., & Pleydell-Pearce, C. W. (2008). Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology (Berl), 195(4), 569-577. doi:10.1007/s00213-007-0938-1

  10. Einother, S. J., & Giesbrecht, T. (2013). Caffeine as an attention enhancer: reviewing existing assumptions. Psychopharmacology (Berl), 225(2), 251-274. doi:10.1007/s00213-012-2917-4

  11. Lieberman, H. R., Tharion, W. J., Shukitt-Hale, B., Speckman, K. L., & Tulley, R. (2002). Effects of caffeine, sleep loss, and stress on cognitive performance and mood during U.S. Navy SEAL training. Sea-Air-Land. Psychopharmacology (Berl), 164(3), 250-261. doi:10.1007/s00213-002-1217-9

  12. Leathwood, P. D., & Pollet, P. (1982). Diet-induced mood changes in normal populations. J Psychiatr Res, 17(2), 147-154.

  13. Morgan, A., & Stevens, J. (2010). Does Bacopa monnieri improve memory performance in older persons? Results of a randomized, placebo-controlled, double-blind trial. The Journal of Alternative and Complementary Medicine, 16(7), 753-759.

  14. Smith, A. (2002). Effects of caffeine on human behavior. Food Chem Toxicol, 40(9), 1243-1255.

  15. 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. Sci Transl Med, 7(305), 305ra146. doi:10.1126/scitranslmed.aac5125

  16. Van Dam, R. M., Pasman, W. J., & Verhoef, P. (2004). Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations. Diabetes care, 27(12), 2990-2992.

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