Caffeine is a central nervous system stimulant that temporarily wards off drowsiness and restores alertness. It is a natural alkaloid found in coffee beans, tea leaves, and cacao pods. Caffeine acts primarily by blocking the action of adenosine, a neurotransmitter that promotes sleep, thereby increasing alertness and reducing fatigue. It is widely consumed in beverages and is known for its bitter taste. Caffeine also has diuretic properties and can enhance physical performance. Its consumption is generally regarded as safe in moderate amounts, but excessive intake can lead to side effects such as insomnia, jitteriness, and increased heart rate.