Kapeina

Kapeina, known in English as caffeine, is a natural stimulant of the central nervous system. It is the most widely consumed psychoactive substance worldwide and occurs naturally in coffee beans, tea leaves, cacao beans, guarana, and kola nuts. Caffeine is also added to soft drinks, energy drinks, and some medications. The name caffeine derives from German Kaffein; it was first isolated in 1819 by the German chemist Friedlieb Runge.

Chemistry: Caffeine is a methylxanthine, specifically 1,3,7-trimethylxanthine, with the empirical formula C8H10N4O2. It is a lipophilic molecule that crosses the blood–brain barrier.

Pharmacology: Caffeine promotes wakefulness mainly by antagonizing adenosine receptors (A1 and A2A) in the brain. This reduces adenosine-mediated inhibition and increases neuronal activity, leading to heightened arousal and the release of other neurotransmitters such as dopamine. It can improve attention, reaction time, and perceived effort during physical tasks.

Pharmacokinetics: After ingestion, caffeine is rapidly absorbed, reaching peak plasma levels in about 30–60 minutes. In healthy adults, the half-life is typically 3–5 hours, but it varies with age, pregnancy, liver function, smoking, and other medications. Caffeine is metabolized mainly by the liver to theobromine, paraxanthine, and theophylline.

Safety and regulation: In most adults, moderate caffeine intake is considered safe, with daily amounts up to about 400 mg commonly cited as a general upper limit. Higher doses can cause insomnia, anxiety, palpitations, or upset stomach. Dependence and withdrawal symptoms, such as headaches and fatigue, may occur with regular use. Pregnant or breastfeeding individuals, and those with certain medical conditions, are often advised to limit intake.