POSSIBLE INHIBITORY EFFECT OF LITHIUM ON PERIPHERAL CONVERSION OF THYROXINE TO TRIIODOTHYRONINE - A PROSPECTIVE-STUDY

The effect of lithium on thyroid function was studied in 18 neurolepti c-treated male chronic schizophrenic in-patients. Lithium carbonate wa s administered for 8 weeks at a dosage giving a mean serum level of 0. 79 mmol/l. Blood was obtained just before and after 8 weeks of lithium administration to determine the serum free thyroxine (free T-4) level s, free triiodothyronine (free T-3) levels and thyrotropin (TSH) level s. Overall, free T-4 and TSH levels significantly increased whereas fr ee T-3 levels did not change. Two (11%) patients had abnormally increa sed free T-4 levels and abnormally decreased free T-3 levels after 8 w eeks of lithium administration. These findings suggest that lithium ma y inhibit the peripheral conversion of free T-4 to free T-3 in some su sceptible patients.