The warning has been prompted by a case where a 13-year-old boy in Naples ended up in hospital after chewing two packets of the stimulant gum - the packs would have contained around 320 milligrams of caffeine and he had eaten them over a four-hour period.

Doctors warn that chewing gum containing caffeine can be dangerous if used in excessive quantities by children and teenagers and have called for greater control on the use and sale of stimulant gum to youngsters.

The boy apparently returned home from school agitated and aggressive in contrast to his normal behaviour - he denied feeling stressed or having used drugs or stimulants but complained of abdominal discomfort, increased and painful passing of urine and prickling sensations in his legs, he was also restless and his breathing, heart rates and high blood pressure were raised.

His parents became concerned and took him to the hospital emergency department where his condition improved overnight and he was discharged after doctors diagnosed his condition as caffeine intoxication worsened by the fact that since he was not a regular drinker of tea or coffee, he was even more sensitive to the compound.

They say the use of stimulant chewing gum should be considered in cases of caffeine intoxication and there is a high risk of intoxication in children and teenagers in view of general caffeine-naivety, and the unrestricted sale of these substances.

The case is published in the current issue of the Lancet.