In order to investigate (a) the effects of 6 weeks’ neuroleptic treatment on the pituitary-thyroid axis in 25 male schizophrenic patients, and (b) the diurnal variation in the thyrotropin (TSH) and prolactin (PRL) responses to thyrotropin-releasing hormone (TRH) in these patients, the TRH stimulation test was performed in each of them at 14.00 and 24.00 h of the same day, both before and after 6 weeks’ treatment with neuroleptics (chlorpromazine or fluspirilene). Also, serum thyroxine (T₄), in vitro radioactive triiodothyronine uptake (RT3 U) and free-thyroxine index (FTI) values were estimated from the pre-TRH blood sample. We found no evidence of diurnal variation in the TSH response to TRH in the schizophrenic patients, before or after 6 weeks’ neuroleptic treatment. Only drug-free schizophrenic patients had significantly higher PRL responses to TRH at 14.00 h than those at 24.00 h. After 6 weeks’ neuroleptic treatment, schizophrenic patients tended to have lower FTI values; also, they had significantly higher basal TSH and PRL values, as well as significantly augmented TSH and PRL responses to TRH, in comparison to their pretreatment values. These findings render possible the diagnosis of subclinical hypothyroidism in neuroleptic-treated schizophrenic patients.

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