By Helen Sewell of BBC Science

Children across the US are increasingly being prescribed mood-altering drugs which have only been approved for adults.

Although the use of stimulants and anti-depressants among toddlers is going up, a report published in the Journal of the American Medical Association claims no-one knows what effects these can have on very young children.

Researchers at the University of Maryland studied the medical records of more than 200,000 youngsters aged between two and four.

Their work has revealed that the use of both stimulants and anti-depressants is becoming more widespread.

Dr Julie Zito who led the research team, is concerned about the use of such powerful drugs because their effects on very young children have not been monitored.

'Inappropriate'

Dr Zito says one study showed that four to six-year-olds can react differently from older children to a particular drug.

But there are no studies of the side-effects on children under four.

Dr Zito is also worried about research which shows that anti-depressants do not work on children aged five to nine.

She says a child's physiological and mental development could be impeded by the long-term use of such drugs.

She questions whether it is appropriate to diagnose very young children with conditions such as attention deficit disorder, hyperactivity and depression.

And she urges families with children on these psychiatric drugs to watch carefully for new behavioural problems and personality changes.