Untold numbers 0f kids may be prescribed antipsychotics on an off-the-label basis every year, but the FDA held back from giving Johnson & Johnson its blessing to market the drug officially to teenagers suffering from schizophrenia.

The agency has issued an approvable letter in response to the drugmaker’s request to market Risperdal for schizophrenia in youngsters between 13 adn 17, and for short-treatment of bipolar mania associated with bipolar I disorder in kids between 10 and 17. J&J was quick to note, however, that the FDA didn’t request new studies, according to its statement today.

Although Risperdal was approved last fall for kids with autism, there’s a growing controversy over the increasing prescribing of antipsychotics for youngsters due to side effects including weight gain and diabetes. A recent report from Medco Health Solutions, the pharmacy benefits manager, found that antipsychotic usage rose more than 117 percent in girls and almost 71 percent in boys between 2001 and 2006. The FDA also delayed approving Lilly’s Zyprexa for kids last April.

“The FDA is giving approvable letters for everything under the sun these days,” Ira Loss, who tracks the drug industry for Washington Analytics, tells Bloomberg News. “And in this case they are particularly gun shy because this is about kids and there are known side effects.”

The wire service notes that an estimated 1 in every 100 people has schizophrenia. Meanwhile, Risperdal sales rose 18 percent last year and sales of Ability, which Bristol-Myers Squibb hopes the FDA will approve for teenagers, rose 41 percent. Overall, scrips for antipsychotics for patients age 20 or younger rose sixfold from 1993 to 2002, from 201,000 to 1.22 million, according to a study published last year in the Archives of the Journal of the American Medical Association.

Of course, FDA approval of antipsychotics for teenagers would encourage pediatricians and primary-care docs to prescribe the drugs as well, said Mark Olfson, lead author of the JAMA study and a Columbia University professor. “These antipsychotics will follow the same path as Prozac,” he tells Bloomberg. “The FDA label gives physicians outside psychiatry some reassurance and confidence in prescribing these medications.”

“There is a very likely possibility that the FDA approval of a teenage indication will provide a false sense of security,” psychiatrist Stefan Kruszewski, of Harrisburg, Pennsylvania, wrote the FDA in a letter opposing clearance of the drugs, according to Bloomberg. “Approval would function as the means by which aggressive pharmaceutical marketing could easily persuade more practitioners to prescribe more potent medications.”