Caffeine

for the coffee plant, see coffea (botany).

1,3,7-trimethylxanthine (also known as caffeine) is a naturally-occurring stimulant substance of the xanthine class. notable effects include stimulation, wakefulness, enhanced focus and motivation. it is the most widely consumed psychoactive substance in the world.

caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants where it acts as a natural pesticide, as well as enhancing the reward memory of pollinators. it is most commonly consumed by humans in infusions extracted from the seed of the coffee plant and the leaves of the tea bush, as well as from various foods and drinks containing products derived from the kola nut.

unlike many other psychoactive drugs, caffeine is legal and unregulated in nearly all parts of the world. beverages containing caffeine, such as coffee, tea, soft drinks, and energy drinks, enjoy great popularity. caffeine is the most commonly used drug in the world, with 90% of adults in north america consuming it on a daily basis. global consumption of caffeine has been estimated at 120,000 tonnes per year, making it the world’s most popular psychoactive substance. this amounts to one serving of a caffeinated beverage for every person every day.

chemistry

caffeine, or 1,3,7-trimethylpurine-2,6-dione, is an alkaloid with a substituted xanthine core. xanthine is a substituted purine comprised of two fused rings: a pyrimidine and an imidazole. pryimidine is a six-membered ring with nitrogen constituents at r₁ and r₃; imidazole is a 5 membered ring with nitrogen substituents at r₁ and r₃. xanthine contains oxygen groups double-bonded to r₂ and r₆.

caffeine contains additional methyl substitutions at r₁, r₃ and r₇ of its structure. these are bound to the open nitrogen groups of the xanthine skeleton. it is an achiral aromatic compound.

pharmacology

the principal mechanism of action of caffeine is as a nonselective antagonist at the adenosine a₁ and a_2a receptors. during waking periods, the brain
levels of the neurotransmitter adenosine steadily increase and trigger fatigue and sleepiness. the caffeine molecule is structurally similar to adenosine, which enables it to bind to adenosine receptors on the surface of cells without activating them, thereby acting as a competitive inhibitor.

alongside this, caffeine also has effects on most of the other major neurotransmitters, including dopamine, acetylcholine, serotonin, and, in high doses, on norepinephrine, and to a small extent epinephrine, glutamate, and cortisol. at high doses, exceeding 500 milligrams, caffeine inhibits gaba neurotransmission. gaba reduction explains why caffeine increases anxiety, insomnia, rapid heart and respiration rate at high dosages.

metabolites

caffeine is metabolized in the liver by the cytochrome p450 oxidase enzyme system, in particular, by the cyp1a2 isozyme, into three dimethylxanthines, each of which has its own effects on the body: