More than a third of children and teenagers taking certain antipsychotic drugs became overweight or obese in the first three months of treatment, a new U.S. study has found.

A newer class of drugs known as atypical antipsychotic medications can be lifesaving for young people with schizophrenia, bipolar disorder or severe aggression associated with autism, according to an editorial accompanying the study in Wednesday's issue of the Journal of the American Medical Association.

But the widespread use of the drugs should be reconsidered, given the risk of weight gain and the long-term risk of cardiovascular and metabolic problems, wrote Dr. Christopher Varley and Dr. Jon McClellan of Seattle Children's Hospital.

For the study, the researchers looked at 205 children and teens aged four to 19 with bipolar disorder, schizophrenia and disruptive or aggressive behaviour spectrum disorders.

Side-effects of the drugs included weight gain, obesity, hypertension, cholesterol and glucose problems that can lead to heart problems and diabetes, Dr. Christoph Correll of Zucker Hillside Hospital and the Feinstein Institute for Medical Research in New York and his colleagues reported.

After about 11 weeks, the average weight gain among study participants was:

• 18.7 pounds (8.5 kg) for Eli Lilly's Zyprexa or olanzapine.
• 13.4 pounds (3.5 kg) for AstraZeneca's Seroquel or quetiapine.
• 11.7 pounds (3.5 kg) for Johnson & Johnson's Risperdal or risperidone.
• 9.7 pounds (4.4 kg) for Bristol-Myers Squibb's Abilify or aripiprazole.
• 0.4 pounds in the untreated comparison group.

Overall, 10 per cent to 36 per cent of the subjects became overweight or obese within 11 weeks of starting antipsychotic drug treatment.

Other adverse metabolic changes were found for each drug, including cholesterol and blood sugar changes for olanzapine and higher cholesterol or blood sugar levels for aripiprazole.

The study's authors recommended that if children and adolescents are started on antipsychotic medication, there should be greater monitoring for heart and metabolic effects.

Health Canada has not approved atypical antipsychotics for children, but in July, researchers in British Columbia reported the number of Canadian children taking the medications anyway has increased tenfold over the past decade.