The drugs have not been fully tested in children
Increasing numbers of UK children are being prescribed unlicensed anti-psychotic drugs, research suggests.
The drugs are used to treat a range of conditions, from hyperactivity to autism, the study, to be published in Pediatrics found.
But the long-term safety of using them for children has not been established.
The numbers remain small, but grew from 0.39 per 1,000 under-18s in 1992 to 0.77 per 1,000 in 2005.
The largest increase was seen among the seven to 12 age group.
A number of short trials have suggested that drugs such as ripseridone for instance can be very effective in calming children with autism and some behavioural problems.
But experts have said it must be used with caution among the under 15s.
"There is no doubt these drugs can be very effective," says Professor Ian Wong of the London School of Pharmacy, who caried out the research.
"But we do not know the long-term consequences - especially their impact on a young, developing brain.
"Parents should not rush to take their child off the medication if it is working, but they should talk to regularly to a specialist and make sure there are frequent reviews."
While these drugs are licensed for adults, there has been a lack of clinical trials to back up their use in children except for certain conditions such as schizophrenia.
This means that doctors can precribe them, but do so on their own responsibility.
Some experts have suggested that in addition to impacting upon a child's growing brain, there may also be implications for the cardiovascular system.
Professor Wong said while there were children who died while on the drugs, there was nothing to suggest that their deaths were caused by the medication itself.
"It is much more likely to be a serious underlying condition, of which the behavioural problems the drug treats are merely a symptom," he said.
The increasing use of the drugs in this country follows a huge rise in prescriptions in the US.
There, children as young as two are reportedly being diagnosed with conditions such as Attention Deficit Hyperactivity Disorder (ADHD) and prescribed such anti-psychotic drugs accordingly.
Professor Wong, whose research is due to be published next month, said while the UK did increasingly seem to be going down the same path as the US, he had yet to come across a single incident of an under four being placed on the drugs.
Professor David Healy, an expert in psychological medicine at Cardiff University said anti-psychotic drugs should only be used on children with extreme caution and very irregularly. He said it was rare that they were really necessary.
He said they had been shown to interefere with both the cardiovascular and respiratory systems. In addition, weight gain was a common side effect, raising the risk of diabetes.
Professor Healy said: "There is no end to the problems drugs can cause so we really need to restrict the conditions which people should get them for so that the risks are warranted."
The Medicines and Healthcare products Regulatory Agency (MHRA) said it was down to individual prescribers to decide whether the drugs would benefit a patient.
But a spokeswoman said drugs were monitored closely for adverse reactions.