Everyday Science: How Caffeine Works

By Iman Yaser

Every morning, millions of students reach for caffeine before they reach for their textbooks. In fact, university students consume substantially more caffeine than the general population, averaging ~159 mg per day, according to one study.¹ Whether it’s coffee before an early lecture or an energy drink during a late-night study session, caffeine has become a highly relied on "study tool” across campuses. But what exactly is this molecule doing to our brains and why does it sometimes sharpen focus while other times it leaves us jittery? Understanding the answers to these questions requires diving into the biology of caffeine.

Caffeine belongs to a class of compounds called xanthines.² Its primary action involves blocking adenosine receptors in the brain, therefore preventing the adenosine from binding to them, a process associated with tiredness and reduced neural activity.² By inhibiting adenosine, caffeine can increase alertness, reduce perceived fatigue and enhance the communication between neurons.² Caffeine also promotes the release of neurotransmitters such as dopamine and norepinephrine, contributing to increased energy, improved mood and more rapid processing of information.^2,3 These combined effects explain why we feel “switched on” after consuming coffee.

For students, caffeine’s cognitive effects matter most when they influence how well we learn, recall and perform under pressure. Research consistently shows that moderate caffeine intake can improve attention, working memory, reaction time and sustained focus; all core components of academic performance.^3,4 These improvements can make studying feel more productive, lectures easier to follow and dense readings more manageable. Several studies also suggest improvements in processing speed, vigilance and cognitive persistence, which can improve performance on tasks like timed tests or problem-solving activities.³ Some evidence also points to improved confidence and perceived readiness, which is helpful in activities such as giving presentations or participating in discussions.⁵

Beyond academics, caffeine’s effects extend to athletic performance, social routines and mood regulation. Moderate caffeine intake has been shown to improve physical endurance, enhance motivation and provide a short-term mood lift for many individuals.² Additionally, on campus, caffeine often acts as both a stimulant and a social ritual necessary for fueling conversations, study groups and early-morning commutes.

However, these benefits depend heavily on dose, timing and individual tolerance and sensitivity.³ High doses (typically above 400 mg/day for adults) can lead to anxiety, restlessness and impaired concentration; effects that may undermine test performance rather than improve it.^3,4 For most students, the optimal range tends to fall around 1-3 mg/kg of their body weight.³

One of caffeine’s most significant consequences lies in its impact on sleep. Because caffeine has a half-life of 5-6 hours, consuming it late in the day can reduce total sleep time by increasing the time it takes to fall asleep.⁶ Even when students believe caffeine “doesn't affect” their sleep, objective studies show measurable disruptions to overall sleep with evening caffeine consumption.⁶ Since sleep quality strongly affects memory, mood and cognitive performance, poor sleep can undermine caffeine’s daytime benefits. Therefore, students who rely on caffeine to “fix” exhaustion may find themselves trapped in a cycle of poor sleep, fatigue, consuming caffeine and subsequently more disrupted sleep. However, recognizing this mechanism can help prevent caffeine dependence and support healthier study routines.

As with any psychoactive substance, awareness is essential. Caffeine affects people differently depending on genetics, metabolism and tolerance.⁷ Some students metabolize it quickly and feel the effects fade within hours while others metabolize it slowly and experience stronger or longer-lasting effects even at low doses.⁷ A common outcome is the caffeine “crash,” an abrupt drop in energy that occurs when caffeine levels fall, allowing adenosine, the molecule caffeine suppresses, to rush back into its receptors.⁸ This rebound can bring sudden fatigue, irritability or difficulty concentrating, making the energy dip feel sharper than ordinary tiredness.⁸ Tolerance also shapes caffeine’s impact: with repeated use, the brain gradually increases the number of adenosine receptors, reducing caffeine’s ability to block them.⁹ As a result, the same dose produces weaker stimulant effects, leading students to feel that caffeine has “stopped working.”⁹ This often drives students to increase intake, with sensitivity returning only after several days to weeks of reduced consumption.⁹ Therefore, recognizing these individual differences and noticing how caffeine shifts one’s sleep, focus and anxiety can help students decide when and how much caffeine works best for them.

Overall, caffeine is far more than a simple compound consumed casually, it's a psychoactive compound that directly shapes how students think, perform and feel. Its effects can sharpen focus, support learning and increase mental energy, but only when used strategically and safely. Therefore, understanding the science behind caffeine can empower students to use it intentionally, not reflexively, to maximize its benefits while avoiding the dangers of overuse.

References

1. Mahoney CR, Giles GE, Marriott BP, et al. Intake of caffeine from all sources and reasons for use by college students. Clin Nutr. 2019;38(2):668-675. doi: 10.1016/j.clnu.2018.04.004

2. Nehlig A. Is caffeine a cognitive enhancer? J Alzheimers Dis. 2010;20 Suppl 1:S85-94. doi: 10.3233/JAD-2010-091315

3. Einöther SJ, Giesbrecht T. Caffeine as an attention enhancer: reviewing existing assumptions. Psychopharmacology (Berl). 2013;225(2):251-74. doi: 10.1007/s00213-012-2917-4

4. Cappelletti S, Piacentino D, Sani G, Aromatario M. Caffeine: Cognitive and physical performance enhancer or psychoactive drug? Curr Neuropharmacol. 2015;13(1):71-88. doi: 10.2174/1570159X13666141210215655

5. Smit HJ, Rogers PJ. Effects of low doses of caffeine on cognitive performance, mood and thirst in low and higher caffeine consumers. Psychopharmacology (Berl). 2000;152(2):167-73. doi: 10.1007/s00213000050

6. Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med. 2013;9(11):1195-200. doi: 10.5664/jcsm.3170

7. Yang A, Palmer AA, de Wit H. Genetics of caffeine consumption and responses to caffeine. Psychopharmacology (Berl). 2010;211(3):245-57. doi: 10.1007/s00213-010-1900-1 

8. James JE, Rogers PJ. Effects of caffeine on performance and mood: Withdrawal reversal is the most plausible explanation. Psychopharmacology (Berl). 2005;182(1):1-8. doi: 10.1007/s00213-005-0084-6

9. Fredholm BB. Notes on the history of caffeine use. Handb Exp Pharmacol. 2011;(200):1-9. doi: 10.1007/978-3-642-13443-2_1