Coffee
The caffeine in coffee is the stimulant that instantly invigorates us when we are tired. It expands the blood vessels, increases the pulse rate and stimulates the digestive system. Caffeine is also found in cocoa and tea. This is the reason a stimulating hot drink of cocoa is very invigorating for us. Caffeine is a compound that is addiction forming ands that is the reason why we look for a good cup of coffee in the morning. When we can not get a cup of hot coffee we feel a slight head ache. This is due to caffeine withdrawal syndrome in the brain.