Caffeine

Caffeine is a central nervous system stimulant and the most widely consumed psychoactive drug in the world. It is a naturally occurring alkaloid of the xanthine class, chemically known as 1,3,7-trimethylxanthine (C8H10N4O2). Caffeine occurs in coffee beans, tea leaves, cacao beans, kola nuts, yerba mate, and guarana, and it is also added to many foods, beverages, and medicines.

Pharmacology and mechanism: Caffeine acts mainly by antagonizing adenosine receptors A1 and A2A in the brain, reducing the perception of fatigue and increasing alertness. It also promotes the release of neurotransmitters such as dopamine and norepinephrine. After ingestion, caffeine is rapidly absorbed, with peak plasma levels occurring within about 30 to 60 minutes. The elimination half-life in healthy adults is typically 3 to 5 hours, but varies with age, pregnancy, liver function, smoking, and other factors.

Effects, uses, and patterns: In moderate doses, caffeine can improve attention, reaction time, and some aspects of memory. Higher doses may cause anxiety, jitters, insomnia, or tachycardia. Caffeine is widely consumed in coffee, tea, soft drinks, and energy products, and it is also an ingredient in certain medications and weight-management products.

Safety and guidelines: For most healthy adults, daily intake up to about 400 mg is considered acceptable, though lower limits apply to pregnant individuals and those with certain health conditions. Abrupt cessation after regular use can lead to withdrawal symptoms such as headaches and fatigue.

History: Caffeine was isolated in 1819 by Friedlieb Runge. Its long-standing cultural use continues to be studied for health effects and safety.