Former U.S. Food and Drug Administration Commissioner Dr. David Kessler testified Thursday in Philadelphia's first Risperdal trial that Johnson & Johnson knew about the drug's ability to raise levels of the hormone that causes male breast growth.

Under direct examination in Philadelphia Court of Common Pleas Judge Ramy I. Djerassi's courtroom by the plaintiff's lawyer, Thomas R. Kline, Kessler said J&J—and by extension, its subsidiary and the drug's manufacturer, Janssen Pharmaceuticals—had data from several studies indicating that Risperdal's elevation of the hormone prolactin presented an increased risk of gynecomastia in boys.

Risperdal is an antipsychotic drug the FDA approved for use in adults that has been prescribed off-label to children with autism and behavioral disorders, prior to being approved for children, plaintiffs alleged.