1. (I) Profound alterations of the hypothalamic-pituitary-adrenocortical (HPA) axis regulation were repeatedly shown in depressed patients. The most sensitive challenge test of the HPA axis, the combined dexamethasone/CRH test (DEX/CRH test), shows an overstimulation of ACTH and cortisol in depressed patients. Under tricyclic antidepressant treatment, a normalization of the HPA axis overdrive was found to precede the clinical improvement.

2. (II) Lithium is a well established drug for the treatment of affective disorders. Yet, its exact mode of action and its effects on the HPA axis are still unknown.

Three 4-week studies with each 30 acutely depressed patients (unipolar, SCID I confirmed) were conducted. In study 1, patients refractory to a treatment trial with an antidepressant of at least four weeks were treated with lithium augmentation. In study 2 and 3, drug free patients were treated with lithium monotherapy or citalopram monotherapy respectively. Weekly HAM-D ratings were performed. In each study, the DEX/CRH test was conducted right before and four weeks after initiation of the pharmacotherapy.

All three pharmacological strategies showed good antidepressive efficacy. Both lithium monotherapy and lithium augmentation led to a (for most parameters significant) increase in the HPA axis activity. In contrast, citalopram monotherapy resulted in a decrease of the hormone response to the DEX/CRH test.