A world-first New Zealand study of children's treatment with "atypical antipsychotic" drugs is providing new insights into why they are being prescribed and what adverse reactions can result.

The Intensive Medicines Monitoring Programme (IMMP) study investigated the safety and use of the drugs in all under-16-year-olds in New Zealand prescribed them between April and July in 2003.

Adverse reactions in the children were monitored until the end of November 2004 and doctors were surveyed on what particular diagnoses and symptoms prompted the prescriptions.

Co-author Dr Mira Harrison-Woolrych says this is the first study anywhere to paint a comprehensive, real-life picture of how the increasingly-prescribed second-generation antipsychotics are being used in children.

Their findings appear in the international journal, Drug Safety.

More than 90 per cent of the prescriptions in the 420 children were for Risperidone, sold under the trade names Risperdal and Ridal in New Zealand. Risperidone was added to the list of government-subsidised medicines in 1998.

Adverse events were identified in 30 per cent of the children and the researchers linked one-third of these to the antipsychotics.

"Weight gain, tooth decay and sleepiness were the most common adverse events we found," says Dr Harrison-Woolrych who directs the IMMP, which is based at the University of Otago.

An unexpected finding was that symptoms of depression - previously unidentified as an adverse reaction of risperidone in children - emerged in four children during their treatment, she says.

Child psychiatrist and co-author Dr Juan Garcia-Quiroga says while it is not certain that risperidone use was responsible, people need to be aware of the possible link.

"More research is required, but because of the potentially serious consequences, clinicians and carers should look out for the emergence of these symptoms," says Dr Garcia-Quiroga.

As well as gathering comprehensive data on the adverse reactions, the researchers also investigated the children’s diagnoses and which symptoms were being targeted.

They found conduct disorders and attention deficit and hyperactivity disorder were the most common diagnoses reported in the children, followed by autism, Asperger's syndrome and other developmental disorders.

A unique feature of the study was that it asked which specific symptoms had prompted treatment with the medicines and this approach yielded clinically relevant data, says Dr Garcia-Quiroga.

Aggression and difficult behaviours were found to be the most common target symptoms, he says.

The United Kingdom health medicines regulatory body has already shown interest in the IMMP findings, says 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.

"By taking advantage of the IMMP's unique prescription event monitoring and record linkage capabilities we were able to add important knowledge about this area."