Wolff–Chaikoff effect

The Wolff–Chaikoff effect is a reduction in thyroid hormone levels caused by ingestion of a large amount of iodine.

It is an autoregulatory phenomenon that inhibits organification (oxidation of iodide) in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream. This becomes evident secondary to elevated levels of circulating iodide. The Wolff–Chaikoff effect lasts several days (around 10 days), after which it is followed by an "escape phenomenon", which is described by resumption of normal organification of iodine and normal thyroid peroxidase function. "Escape phenomenon" is believed to occur because of decreased inorganic iodine concentration secondary to down-regulation of sodium-iodide symporter (NIS) on the basolateral membrane of the thyroid follicular cell.

It may be noted, that, this phenomenon is generally seen only in patients with either autoimmune thyroid disease (eg. Graves disease) or with patients with severe hyperthyroidism.

The Wolff–Chaikoff effect can be used as a treatment principle against hyperthyroidism (especially thyroid storm) by infusion of a large amount of iodine to suppress the thyroid gland. Iodide was used to treat hyperthyroidism before antithyroid drugs such as propylthiouracil and methimazole were developed. Hyperthyroid subjects given iodide may experience a decrease in basal metabolic rate within 24 hours that is comparable to that seen after thyroidectomy. The Wolff–Chaikoff effect also explains the hypothyroidism produced in some patients by several iodine-containing drugs, including amiodarone.