 The Food and Drug Administration has approved sirolimus for suppressing the immune system of patients who have had a kidney transplant to reduce the risk of organ rejection. The drug does not have certain side effects that have caused problems for patients treated with other immunosuppressants, such as: prednisone weight gain, round face, diabetes, weak and fractured bones, and cataracts; cyclophosphamide fertility problems, bladder injury and bladder cancer, and other cancers; chlorambucil fertility problems, seizures, acute leukemia, and other cancers; and cyclosporine kidney toxicity, increased facial hair, and seizures. 