Caffeine Caffeine is a stimulant. A stimulant is something that speeds up the body or mind.
Caffeine affects people in different ways.
Most adults are not bothered by one cup of instant coffee or a can of soda. In small doses, caffeine can make you feel alert. Most people don't know that caffeine is a habit-forming drug. A person dependant on caffeine is likely to suffer from headaches and feel tired between doses. When caffeine is stopped, they may have headaches, an upset stomach, tiredness and jittery nerves.