methylxanthinescaffeine

Caffeine is a methylxanthine alkaloid and the most widely consumed psychoactive stimulant in humans. Its chemical name is 1,3,7-trimethylxanthine, and it is classified among purine alkaloids.

Caffeine occurs naturally in coffee beans, tea leaves, cacao beans, and kola nuts, and is added to a wide range of foods, beverages, and medicines. Typical caffeine content varies by source: coffee generally provides the largest amounts, followed by tea, soft drinks, and chocolate products.

The primary mechanism of action is antagonism of adenosine receptors, especially A1 and A2A in the brain, which reduces neuronal activity related to sleep and increases wakefulness and attention. At higher concentrations it can inhibit phosphodiesterase and raise intracellular cAMP, contributing to stimulatory effects. Caffeine also increases release of certain neurotransmitters and can produce mild diuretic and sympathetic nervous system effects.

Pharmacokinetics: caffeine is rapidly absorbed from the gastrointestinal tract and reaches peak plasma levels within about 30 to 60 minutes after ingestion. In healthy adults, the elimination half-life is roughly 3 to 5 hours, but the duration and clearance are influenced by factors such as pregnancy, liver function, and smoking (which can shorten half-life). It is metabolized in the liver to several compounds, primarily paraxanthine, theobromine, and theophylline.

Uses and safety: caffeine is consumed for its wake-promoting and mood-enhancing effects. Medically, caffeine citrate is used to treat neonatal apnea. Moderate intake is generally regarded as safe for most adults, though excess consumption can cause insomnia, anxiety, palpitations, and digestive upset, and dependence can develop with heavy use. Guidance typically recommends up to about 400 mg per day for healthy adults, with lower limits for pregnant individuals (often around 200 mg per day).