Effect of dexamethasone on plasma prolactin and cortisol levels in psychiatric patients.

In addition to its ability to decrease plasma cortisol levels, dexamethasone can also significantly decrease plasma prolactin levels. In 52 psychiatric patients, including 26 patients with primary major depression or schizoaffective depression, primarily affective type, there was a significant association between nonsuppression of plasma cortisol and prolactin after administration of dexamethasone. These results suggest that the abnormal cortisol response to dexamethasone in some psychiatric patients may be due to a pituitary gland abnormality rather than to a limbic system abnormality. The sensitivity and specificity of the dexamethasone suppression test for endogenous depression were less than previously reported.