Antidepressants and thyroid hormone levels

We assessed the effect of treatment with the tricyclic antidepressant, desipramine, on peripheral thyroid hormone levels in 28 severely depressed patients. Only those whose depression responded showed a decrease in their thyroxine levels without alteration of other thyroid function tests. In a second study involving 38 depressed patients, we observed an increased response to antidepressant treatment with the addition of triiodothyronine but not equivalent doses of thyroxine (T4). The finding is consistent with the decreases in plasma T4 levels which accompany an antidepressant response to desipramine.