KEY POINTS:
Doctors are unnecessarily prescribing children powerful antipsychotic drugs which can lead to drowsiness, depression, tooth decay and weight gain.
The findings were part of a national study investigating the safety and use of a relatively new class of antipsychotic drug on the under-16s.
More than 90 per cent of prescriptions for the 420 children involved in the study were for risperidone, which is sold under the trade names Risperdal and Ridal. It has been a government subsidised medicine since 1998, with about 600 children being prescribed the drug.
The study by the Intensive Medicines Monitoring Programme found harmful side-effects in 30 per cent of the children on the drugs classed as "atypical antipsychotics". A third of these were linked to the drugs, say the researchers.
Co-author Mira Harrison-Woolrych said this was the first study in the world to paint a comprehensive, real-life picture of how the increasingly-prescribed second-generation antipsychotics are being used in children.
"Weight gain, tooth decay and sleepiness were the most common adverse events we found," said Dr Harrison-Woolrych, who directs the monitoring programme based at Otago University.
The finding of higher levels of tooth decay was unexpected, as were symptoms of depression in four children - a previously unidentified adverse reaction of risperidone.
"The children that developed the symptoms of depression didn't have depression to start with ... We were very cautious and only coded those events where the psychiatrist or the doctor had definitely said the child had developed symptoms of depression." There were also seven other children whose symptoms, while not definitive, suggested depression.
Dr Harrison-Woolrych said with these children, there were often other factors involved.
"We're not saying that we've definitely shown that risperidone causes depression in children, what we're saying was this was an unexpected finding. We think it needs further work and we think that clinicians, doctors and carers of children should just be aware that this is a potential finding."
As well as gathering data on adverse reactions, the researchers also investigated the children's diagnoses and the symptoms being targeted by the drugs. They found conduct disorders and attention deficit and hyperactivity disorder to be among the most common diagnoses, followed by autism, Asperger's syndrome and other developmental disorders.
Child psychiatrist and co-author Dr Juan Garcia-Quiroga said aggression and difficult behaviours were found to be the most common target symptoms.
The use of risperidone in these instances was appropriate.
But the study also found doctors prescribing the drug for anxiety and personal developmental disorders as well as sleeping disorders - conditions which were outside the terms of the product licence at the time of the study.
Dr David Menkes, associate professor of psychiatry at Auckland University's Waikato clinical school, said some of the cases where the drug was prescribed was "worrisome".
"Every case has to be judged on its merits, but to be using a powerful antipsychotic drug for insomnia, for example, I think it likely to be questionable."
The UK's health medicines regulatory body had already shown interest in the findings, said Dr Harrison-Woolrych.
"While prescriptions of these medicines in children and adolescents have increased vastly worldwide, there has been a lack of good evidence about their long-term safety."
The findings appear in the latest edition of international journal Drug Safety.
