Effect of increased iodide intake on thyroid function in subjects on chronic lithium therapy.

Thyroid function tests were obtained in 10 patients on chronic lithium therapy before and after the administration of potassium iodide 250 mg q.i.d. Mean serum TSH rose by 8.9 muU/ml and mean serum T3 rose from 70 to 101 ng/dl. Two patients became hypothyroid; a third showed a rise in TSH without any change in T3 or T4. A fourth patient developed hyperthyroidism probably secondary to the Jod-Basedow phenomenon. Pharmacologic doses of iodine should be administered with caution to patients on chronic lithium therapy.