TORONTO -- An Ontario study shows one in 20 children and youth have attention deficit hyperactivity disorder and many are prescribed antipsychotic drugs, despite having no other mental health diagnosis.

Attention deficit hyperactivity disorder, or ADHD, causes such symptoms as difficulty concentrating and restlessness.

The study by the Institute for Clinical Evaluative Sciences found almost 12 per cent of kids and youth aged one to 24 with ADHD were prescribed antipsychotics like Risperdal, which were developed to treat schizophrenia.

One in four of the youth who received an antipsychotic drug had no other record of a mental health diagnosis, such as schizophrenia or bipolar disorder.

Senior author Dr. Paul Kurdyak says there are risks associated with antipsychotic medications, such as significant weight gain and the development of diabetes.

The study published in the Canadian Journal of Psychiatry found about 70 per cent of children and youth diagnosed with ADHD were prescribed various medications to treat the disorder, including antipsychotics.

"We don't know why these children and youth with ADHD are on antipsychotics, but there is a risk associated with early antipsychotic exposure, so we need to know more about why they are being used so that the benefits can be weighed against the risks," Kurdyak said.