The precise effective dose of caffeine varies for each individual, primarily determined by body size and caffeine tolerance.Caffeine begins affecting the body within less than an hour. For a moderate dose, its effects typically wear off within 3 to 4 hours. Consuming caffeine does not reduce the amount of sleep needed; it merely temporarily dulls the sensation of sleepiness. The dangers of overuse: with long-term, high-dose consumption, caffeine can act as a drug, potentially leading to "caffeine intoxication."
Caffeine intoxication involves addiction and a range of adverse physical and psychological reactions, such as nervousness, irritability, anxiety, tremors, muscle spasms (hyperreflexia), insomnia, and palpitations. Most people consume caffeine for its stimulating effects; many students take caffeine pills during exams, and night shift workers often use them.
Caffeine is a xanthine alkaloid compound and a central nervous system stimulant that temporarily wards off drowsiness and restores energy. Caffeine-containing coffee, tea, soft drinks, and energy drinks are highly popular, making caffeine the world's most widely used psychoactive substance.
In North America, 90% of adults consume caffeine daily.
Many natural sources of caffeine also contain various other xanthine alkaloids, including the cardiac stimulants theophylline and theobromine, as well as other substances such as tannic acid.
Current research indicates specific physiological effects of caffeine on the human body: It effectively combats free radicals that threaten health, which are primary contributors to numerous diseases (e.g., cardiomyopathy, atherosclerosis, stroke, emphysema, Parkinson's disease). Excessive free radicals disrupt metabolic processes, damage cells, and impair organ function.
Cardio-vascular protection: Rich in polyphenolic compounds—potent antioxidants—it can delay LDL oxidation by up to three times, dissolve blood clots, and prevent thrombus formation. Coffee also enhances vasoconstriction, preventing vasodilation-induced headaches. Additionally, moderate coffee consumption strengthens myocardial contractility, promotes blood circulation, and helps prevent cardiovascular diseases.