How Much Is Too Much?
A lethal dose of caffeine is approximately 10g or 150mg per kilogram of body weight. This is difficult to exceed accidentally since even caffeine pills and expresso contain only around 1% of this per serving. Some examples of content:
(Taken from National Soft Drink Association statistics (USA))
The caffeine content of any particular coffee or tea can vary greatly even if made by the same person using the same machine and product from batch to batch so these statistics are very loose.
Most people are now at risk from accidental death through excess intake of caffiene, however infants metabolize caffeine very slowly and a dose of 35mg/kg body weight could be lethal. It is therefore important that the caffeine intake of infants is carefully monitored and that caffeine pills, as all other drugs, are kept well out of their reach.
Over 250mg is sufficient for an overdose which may have adverse implications.