RELATIONSHIP BETWEEN PSYCHOTROPIC-DRUGS AND THYROID-FUNCTION - A REVIEW

Some widely used psychoactive drugs, such as tricyclic antidepressants and antipsychotic phenothiazines exhibit iatrogenic effects on the th yroid. These side effects may arise from interactions at different ste ps of thyroid hormone biosynthesis. These drugs can induce a change in iodine capture by thyroid cells or can complex iodine, making it unav ailable for thyroid hormone synthesis and thus decreasing thyroid horm one blood levels; they can also inhibit thyroid peroxidase activity an d thus T-3 and T-4 synthesis or enhance deiodination of T-4 to T-3 or to Rt(3) by stimulation of deiodinase activity. Moreover, tricyclic an tidepressants interfere with the hypothalamic-pituitary-thyroid axis v ia the noradrenergic or serotonergic systems and might therefore decre ase T-4 or T-3 blood levels, respectively. Phenothiazines can induce a utoimmune hypothyroidism, as shown by an increase in the expression of the major histocompatibility complex antigen and by a production of a ntithyroglobulin or antithyroperoxidase antibodies. However, all these mechanisms are only speculative in humans, as they have only been dem onstrated in vitro or in animal experiments. Clinically, thyroid funct ion and affective disorders are closely linked. On one hand, the thera peutic response to antidepressants could be influenced by the thyroid status; on the other hand, the larger the thyroxin decrease induced by antidepressants, the better the therapeutic effect might be. Moreover , cotreatment with thyroid hormones and antidepressant drugs could all ow either a decrease in the rate of treatment failure or a faster reco very from depression. As antipsychotic or antidepressant treatments ar e administered over long periods in humans, their thyroid toxic effect s must be taken seriously. (C) 1998 Academic Press.