Lithium addition in endogenous depressions resistant to tricyclic antidepressants or related drugs: relation to the status of the pituitary-thyroid axis.

Concentrations of TSH, TRH-induced TSH (delta-TSH), T4, FT4, T3, and FT3 were investigated in 20 patients resistant to antidepressants before and after one week of lithium addition. TSH and delta-TSH increased, whereas FT4 and FT3 decreased statistically significantly during this treatment, indicating a slight lithium-induced hypothyroid function. A statistically significant correlation between improvement and the FT3/FT4 ratio after seven days of lithium addition was found. Also, an increase or only a small decrease in FT3 and an augmenting FT3/FT4 ratio during lithium addition were correlated with a favorable outcome. Besides the possibility that a high relative FT3 concentration is an indicator of an unknown somatic condition favorable for improvement, this finding might be directly related to treatment response. It appears conceivable that even within the normal range a sufficient T3 concentration is necessary for an optimal response to lithium addition.