Psychotropic drugs can influence synthesis and metabolism of thyroid hormones at different sites. Generally, lithium, tricyclic antidepressants and phenothiazines lead to a reduction in synthesis and/or metabolism of thyroid hormones. The induction of autoimmune thyroid disorders by lithium and phenothiazines has been proven in animal studies and possibly can also be found in humans. Antipsychotic drugs generally exert their therapeutic effects through a modulation of the monoaminergic and serotoninergic system. At the hypothalamic level, thyrotropin releasing hormone (TRH) is controlled by the monoamonergic system and by serotonin. Depending on the specific species, there is a particular and different influence on the secretion of different hypothalamic-pituitary-thyroid (HPT)-axis hormones.