[Administration of thyroid hormones in therapy of psychiatric illnesses]

This review tries to give the state of the art of the therapeutic use of thyroid hormones in psychiatric disorders, mainly in depression. Four hypotheses suggest an effect in these ailments: 1) a local relative T4 excess present (or better postulated to be present) in the brain of depressed patients is lowered by triiodothyronine (T3), by lowering serum levels of thyroxine (T4), 2) the effect of a depression-mediated cerebral lack of catecholamines is compensated by the T3/T4 induced activation of beta-receptors, 3) a postulated depression-induced local cerebral hypothyroidism can be counteracted by T3 and T4. 4) thyroid hormones increase the cerebral content of serotonin. This may be beneficial in depression, where shortage of serotonin in the brain is accused to be etiologically important. Thyroid hormones have been used so far in the following ways: 1) as T3 monotherapy in depression; 2) initial additive T3 for acceleration of the response to treatment with tricyclic antidepressants (TCA); 3) additive T3 for augmentation of the response to TCA in therapy-resistant patients with depression, 4) as high-dose (250-500 micrograms/die) T4-treatment of "rapid cycling bipolar disorder". Low dose (5-50 mg/die) T3 "augmentation therapy" is the best documented form of treatment with thyroid hormones in depression. The results suggest a convincing benefit for a varying percentage of non responders to therapy with TCA. For the other forms of treatment placebo-controlled double blind studies are not yet available or give conflicting results.