Changes in serum thyroid hormone levels in psychiatric patients treated with second-generation antipsychotics

Introduction: The objective of the study was to evaluate changes in serum thyroid hormone levels in psychiatric patients after second-generation antipsychotic (SGA) treatment, and to determine differences between monotherapy and polytherapy with SGAs, as well as differences between patients with and without a history of antipsychotics. Material and methods: A total of 71 patients with baseline thyroid hormone levels within the normal reference ranges were included in this retrospectively study. Results: After SGAs treatment, the serum levels of free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (TT3), and total thyroxine (TT4) significantly decreased, and serum thyroid-stimulating hormone (TSH) levels significantly increased (changes from baseline: FT3: -0.31 pmol/L, p < 0.001; FT4: -2.71 pmol/L, p < 0.001; TT3: -0.05 nmol/L, p = 0.024, TT4: -12.36 nmol/L, p < 0.001; TSH: 0.46 mIU/L, p < 0.001). One (1.4%) patient had TSH levels higher than 7 mIU/L. Changes in serum levels of TSH and TT3 between patients with or without a history of antipsychotic drugs were significantly different (changes from baseline: TSH: p < 0.001 vs. p = 0.089; TT3: p = 0.013 vs. p = 0.553). Changes in serum TSH levels had a moderate positive correlation with the average daily dose of SGAs (p = 0.007, r = 0.318). Conclusions: After SGA treatment, patients seemed to have a trend of hypothyroidism, but the incidence was low. The preliminary results of this study did not show the necessity of regular monitoring of serum thyroid hormone levels in patients with baseline thyroid hormone levels within the normal reference ranges.