top of page

The Buzz on Caffeine: How Long Does It Last and How Does It Affect Alertness?

A woman ippi

Caffeine, a central nervous system stimulant, is known for its ability to ward off drowsiness and restore alertness. If you're reaching for that cup of coffee, you might wonder just how long that energetic buzz is going to last. Let's dive into the world of caffeine metabolism and its impact on our bodies.

How long caffeine stays in our body

Caffeine's half-life—the time it takes for half of the drug's concentration to be eliminated from the body—varies among individuals. For most healthy adults, the half-life of caffeine is about 3.4 to 5 hours [1]. However, several factors can extend this duration. For instance, during pregnancy, the half-life of caffeine can stretch to an average of 8.3 hours [2].

How The Body Processes Caffeine

How caffeine is processed by the brain for alertness

Caffeine works its magic by blocking the action of adenosine, a neurotransmitter that promotes sleep. By occupying adenosine receptors without activating them, caffeine prevents this sleepy signal from being received, thus promoting wakefulness [3].

How caffeine leaves our bodies

The liver metabolizes caffeine through the cytochrome P450 oxidase enzyme system, specifically the CYP1A2 isoenzyme, which is responsible for demethylating caffeine, leading to its subsequent excretion from the body [10][11].

Individual Variability in Caffeine Metabolism

Why can some people enjoy a late-night espresso without tossing and turning in bed, while others feel jittery after a single morning latte? The answer lies in the complex interplay of genetic factors and lifestyle habits. Research indicates that genetic variations, such as the adenosine A2A receptor gene (ADORA2A), influence an individual's reaction to caffeine [5].

Habitual caffeine consumption plays a role; regular intake can lead to tolerance, meaning more caffeine is required to feel its effects, while infrequent consumers may be more susceptible to its stimulating properties [6].

Age and body mass also contribute to this sensitivity variance. Younger individuals and those with a lower body mass index (BMI) may experience more potent effects due to faster metabolism and lower distribution of caffeine in body fat [7]. Additionally, psychological factors like anxiety sensitivity can heighten one's perception of caffeine's effects, potentially leading to an increased heart rate and alertness that some might find uncomfortable [8].

Individuals with alcoholic hepatic disease have shown significantly prolonged caffeine half-lives, highlighting the role of liver function in caffeine metabolism [9].


Caffeine's ability to keep us alert depends on how quickly our body processes it, which varies widely among individuals. It's a delicate dance between our biology and our favorite pick-me-up beverage. Remember, while caffeine can be a helpful tool for alertness, moderation is key.



  1. Bruce, M., Scott, N., Lader, M., & Marks, V. (1986). The psychopharmacological and electrophysiological effects of single doses of caffeine in healthy human subjects. British Journal of Clinical Pharmacology, 22(1), 81-87.

  2. Knutti, R., Rothweiler, H., & Schlatter, C. (1982). Effect of pregnancy on the pharmacokinetics of caffeine. Archives of Toxicology Supplement, 5, 187-192.

  3. Magkos, F., & Kavouras, S. (2005). Caffeine use in sports, pharmacokinetics in man, and cellular mechanisms of action. Critical Reviews in Food Science and Nutrition, 45, 535-562.

  4. Kalow, W. (1985). Variability of caffeine metabolism in humans. Arzneimittel-Forschung, 35(1A), 319-324.

  5. Rétey, J. V., Adam, M., Khatami, R., Luhmann, U. F., Jung, H. H., Berger, W., & Landolt, H. P. (2007). A genetic variation in the adenosine A2A receptor gene (ADORA2A) contributes to individual sensitivity to caffeine effects on sleep. Clinical Pharmacology & Therapeutics, 81(6), 692-698.

  6. Nehlig, A., & Debry, G. (1994). Caffeine and sports activity: a review. International Journal of Sports Medicine, 15(5), 215-223.

  7. Mitsumoto, H., DeBoer, G. E., Bunge, G., Andrish, J., Tetzlaff, J., & Cruse, R. P. (1990). Fiber-type specific caffeine sensitivities in normal human skinned muscle fibers. Anesthesiology, 72(1), 50-54.

  8. Keogh, E., & Chaloner, N. (2002). The moderating effect of anxiety sensitivity on caffeine-induced hypoalgesia in healthy women. Psychopharmacology, 164, 429-431.

  9. Statland, B., & Demas, T. (1980). Serum caffeine half-lives. Healthy subjects vs. patients having alcoholic hepatic disease. American Journal of Clinical Pathology, 73(3), 390-393.

  10. Sinha, R., Farah, B. L., Singh, B., Siddique, M. M., Li, Y., Wu, Y., ... & Yen, P. M. (2014). Caffeine stimulates hepatic lipid metabolism by the autophagy-lysosomal pathway in mice. Hepatology, 59(4), 1366-1380.

  11. Gressner, O., Lahme, B., Rehbein, K., Siluschek, M., Weiskirchen, R., & Gressner, A. M. (2008). Pharmacological application of caffeine inhibits TGF-beta-stimulated connective tissue growth factor expression in hepatocytes via PPARgamma and SMAD2/3-dependent pathways. Journal of hepatology, 49(5), 758-767.



bottom of page