Drug of Abuse?
Caffeine is currently banned by the International Olympic Committee as a doping agent. It was initially banned in 1964 before being struck from the list of doping agents then returned in 1984. It can be used to raise an athlete's blood sugar level, blood pressure and body temperature, which gives it the potential, in large doses, to enhance performance. It is also banned, together with all other diuretics, because it can be used to cause loss of water, hence weight, from the body in order to conform to weight restrictions.
The World Health Organisation decline to describe caffeine as dangerous: "There is no evidence whatsoever that caffeine use has even remotely comparable physical and social consequences which are associated with serious drugs of abuse".
USA's most popular alertness aid "Vivarin" contains 200mg of caffeine is described as perfectly safe by the United States Food and Drug Administration and the American Psychiatric Association declined to describe it as a drug of abuse or dependence. It is yet to be made available to the rest of the world, however similar less potent aids are available.
It seems that caffeine is relatively safe in small doses, yet in large doses and to high risk groups, pregnant women and children, can be dangerous.