Shares of Corcept Therapeutics ( CORT) plummeted Friday after the company said a late-stage clinical trial intended to prove the effectiveness of its treatment for psychotic major depression missed its goal. In one of three phase III trials, the drug, Corlux, failed to improve a target number of patients' scores on a psychiatric-symptoms rating scale by 50%, the study's main target. Shares slumped 44 cents, or 34%, to 87 cents on trading volume that was much heavier than normal. "The study revealed no meaningful separation in response between patients receiving Corlux and patients receiving placebo," the company said in a press release. Results from a previous trial showed an unusually high patient response to a placebo, added Corcept's president and head of development Dr. Robert Roe. At day 56 of the trial, for example, 95% of patients given the drug, and 95% of patients taking a placebo showed at least a 50% response measured by a specific type of psychiatric-rating scale. Corcept said the results of two of the study's secondary goals were also poor. Despite the findings, Corcept will continue to enroll patients in another phase III study of the drug. Phase III is the stage of trials conducted to support Food and Drug Administration approval.