(NaturalNews) The FDA has begun an investigation into whether atypical antipsychotic drugs such as Zyprexa and Seroquel are more likely to produce abnormal weight gain and diabetes in children than in adults.The announcement came after the agency approved both drugs for use in adolescents between the ages of 13 and 17 for the treatment of severe conditions such as schizophrenia, bipolar disorder and autism.Atypical antipsychotics, also known as "second generation antipsychotics," are known to cause weight gain and metabolic changes that can lead to diabetes. Research suggests that children may be even more vulnerable to this effect. A recent study published in thefound that children and adolescents taking atypical antipsychotics added between 8 and 15 percent to their body mass in only 11 weeks, which was sufficient for many of them to become overweight or obese. The greatest weight gain -- an average of 19 pounds -- was seen with Zyprexa.Zyprexa's label already carries a warning that teenagers are more prone to weight gain, and will soon include new language encouraging doctors to try other treatments first. Because the labels of other antipsychotics do not carry such warnings, however, the FDA is also investigating the other three drugs approved for use in children -- Seroquel, Ablify and Risperdal -- as well as Geodon, which is only approved for adults.Because U.S. law allows doctors to prescribe drugs for unapproved uses at their own discretion, many teenagers are being treated with antipsychotic drugs for behavioral conditions such as attention deficit disorder. No research has been conducted into whether the drugs are effective for these uses, however.Antipsychotics are the best-selling drug class in the United States, with annual sales of $14.6 billion. Zyprexa is the top seller for maker Eli Lilly, with $2.2 billion a year in U.S. sales and $4.7 billion worldwide. Seroquel makes $2.9 billion for AstraZeneca each year in U.S. sales alone, and a total of $4.7 billion globally.Sources for this story include: blogs.wsj.com.