This invention generally pertains to the field of psychiatry. In particular, this invention pertains to the discovery that agents capable of inhibiting the binding of cortisol to its receptors can be used in methods for preventing or reversing cognitive deterioration in adults with Down's syndrome. Mifepristone, a potent specific glucocorticoid receptor antagonist, can be used in these methods. The invention also provides a kit for preventing or reversing cognitive deterioration in a DS patient including a glucocorticoid receptor antagonist and instructional material teaching the indications, dosage and schedule of administration of the glucocorticoid receptor antagonist.