The most widely used drug world-wide is caffeine, a stimulant drug found in tea, coffee, cola drinks, some chocolates and in many painkillers.
Caffeine stimulates the nervous system. In moderate amounts (approx. two cups of coffee) the drug increases wakefulness, reduces fatigue and postpones the onset of sleep. Mental activity is increased and people can perform physically exhausting work for longer.
It is claimed that gastric secretion can be increased by caffeine, raising stomach activity and thereby increasing the risk of stomach ulcers. At high doses the heart muscles are stimulated and blood vessels in the brain narrow. Regular drinkers of tea and coffee (3-5 cups a day) can experience withdrawal effects such as headache and irritability if consumption stops abruptly.
Research into the long-term effects of caffeine is inconclusive. There is concern that the amount of caffeine consumed by young children, particularly in soft drinks and chocolate may lead to hyperactivity.