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Caffeine: Absorption, Distribution, Metabolism Essay

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Updated: Nov 4th, 2021


This paper discusses the metabolism and excretion of caffeine in the human system. Caffeine is a constituent of coffee, cocoa beans, and tea, etc. and it is used as a stimulant that affects the central nervous system. Caffeine is obtained from a plant named alkaloid and it is consumed in its purest form. Its chemical formula is 1, 3, 7 – trimethylxanthine and structure are C8 H10 N4 O2 and its molecular weight is 194.19. It belongs to the family of methylxanthines. It has physiological and pharmacological effects on the different human systems like increased heart rate, respiration, renal activity, and physical performance. It leaves its deep influence on memory, cognition, moods, and alertness.

Absorption and Distribution of Caffeine

Within 45 minutes of ingestion, 99% of caffeine is engrossed in the human system. Tea, chocolate, coffee, or soft drinks like Coke, Pepsi, etc contains caffeine and when caffeine is taken in this form then amalgamation happens all through the gastrointestinal tract, and then it gets engrossed into the water content of each cell of the body. Another way of ensuring complete and rapid absorption of caffeine is through the oral mucosa and chewing caffeinated gum and other preparations. By using these methods for rapid absorption of caffeine, the plasma cells are supposed to have a maximum concentration of caffeine within 15 to 120 minutes. The effect is very rapid if consumed on empty stomach and the absorption gets slowed down due to the presence of food especially fiber in the stomach.

As caffeine passes through the GI tract, there is no hepatic first pass so it remains in the system. It binds with the plasma proteins so is hydrophilic in nature and due to this property, it is completely absorbed into the body. Though it is lipophilic as it can exceed through the cell membranes into the cell, and due to this property it can pass through the blood-brain barrier. It is present in the cells where all the physiological effects of caffeine occur.

Metabolism and Excretion of Caffeine

Caffeine metabolism takes place in the kidneys and the process is catalyzed by the microsomal enzyme systems. The production of paraxanthine and its excretion through urine is the main way of caffeine metabolism. Dimethylxanthine, di and tri-methylallantoin, uracil derivative, and uric acid are produced after the caffeine is being metabolized.

The first step of caffeine metabolism involves the breakdown of 3 – ethyl demethylation to paraxanthine and 70 to 80% of caffeine is metabolized by cytochrome P4501A2 into paraxanthine, theophylline, and theobromine. Immediately after the consumption of caffeine, the paraxanthine and caffeine concentration increases in the body within 8 to 9 hours and it leaves minute traces of toxicology into the blood. Small intakes of caffeine keep these levels at a negligible level but regular consumption results in the increase of paraxanthine in the cells. The sudden cessation in the consumption of caffeine leads to a decrease in the level of paraxanthine and withdrawal symptoms. Paraxanthine is slowly eliminated from the system via urine which is produced in the renal system. The elimination of caffeine occurs between 1.5 to 9.5 hours. This variation in the rate of elimination may be due to individual, physiological and environmental characteristics like pregnancy, obesity, attitude, smoking, use of oral contraceptives, etc. The total clearance occurs at the rate of 0.078 L/h/kg.


Caffeine is absolutely and quickly engrossed in the body after ingestion. It is rapidly distributed due to its hydrophilic and lipophilic characteristics across the membranes including the brain. Physiologically it has a stimulating effect on the system. Regular consumption of caffeine leads to paraxanthine buildup in the cells causing tolerance and withdrawal symptoms. The pace of removal of caffeine from the body depends on physiological and surrounding environmental aspects like smoking, pregnancy, oral contraception, etc.

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1. IvyPanda. "Caffeine: Absorption, Distribution, Metabolism." November 4, 2021. https://ivypanda.com/essays/caffeine-absorption-distribution-metabolism/.


IvyPanda. "Caffeine: Absorption, Distribution, Metabolism." November 4, 2021. https://ivypanda.com/essays/caffeine-absorption-distribution-metabolism/.


IvyPanda. 2021. "Caffeine: Absorption, Distribution, Metabolism." November 4, 2021. https://ivypanda.com/essays/caffeine-absorption-distribution-metabolism/.


IvyPanda. (2021) 'Caffeine: Absorption, Distribution, Metabolism'. 4 November.

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