Use of antipsychotic medications has been associated consistently with weight gain and metabolic disturbances, and a subsequent increased risk for diabetes and cardiovascular disease. Two experiments tested whether CORT 108297, a newly identified selective glucocorticoid antagonist could (i) reduce and (ii) prevent olanzapine-induced weight gain in rats. In the first experiment, rats dosed only with olanzapine gained a statistically significant amount of weight. When vehicle was added to their olanzapine dose, they continued to gain weight; when CORT 108297 was added to their regimen, they lost a significant amount of weight. Rats administered CORT 108297 plus olanzapine had significantly less abdominal fat than those who received olanzapine alone. In the second experiment, rats receiving olanzapine plus CORT 108297 gained significantly less weight than rats receiving only olanzapine. Increasing doses of CORT 108297 were associated with less weight gain.