Effect of mirtazapine on thyroid hormones in adult patients with major depression.

Hypothalamic pituitary thyroid (HPT) axis abnormalities and alterations in major depression are
reported in literature. The aim of our study was to evaluate the effect of mirtazapine on thyroid hormones
after 6 months of therapy in a sample of adult outpatients with Major Depression (MD). 17 adult
outpatients (7 men, 10 women) with MD according to DSM-IV criteria, were included in the study. All
participants had to have met criteria for a major depressive episode with a score of at least 15 on the
Hamilton Depression Rating Scale (HAM-D). Fasting venous blood samples were obtained for
determination of serum Thyroid Stimulating Hormone (TSH), Free T3 (FT3) and Free T4 (FT4)
concentrations both at baseline and after 6 months of therapy. HAM-D scores decreased significantly from
the first day of treatment to the end of the treatment period (P<0.001) and twelve patients (70.6%) were
classified as responders. Asignificant increase in FT3 concentrations was found between baseline and the
end of treatment period (P=0.015) whereas FT4 concentrations decreased (P=0.046). No significant
changes were found in TSH levels. Higher FT4 concentrations at baseline predicted higher HAM-D
scorers both at baseline and at the end of the treatment period. Furthermore, higher FT3 concentrations
at endpoint were found to be predictors of lower HAM-D scores. Long-term treatment with mirtazapine
increases FT3 levels and decreases FT4 maybe involving the deiodination process of T4 into T3.