The effect of lithium on the peripheral turnover of T4 and T3 was investigated in 14 euthyroid subjects using lymphocytes as target cells. Lithium caused a dose-dependent rise in T4 turnover, which did not lead to increased T3 production, but no rise in T3 turnover. A further 3 patients with lithium induced hypothyroidism were studied. Patients with high T4 turnover had high TSH values and in these patients lithium induced a decrease in T4 turnover.
This may lead to the conclusion that the demonstrated effect of lithium in the control group did not cause the low T4 in these patients. In 2 patients defective T4 degradation was demonstrated.