Radioactive iodine is most effective for treating which condition?

Radioactive iodine is most effective for treating Grave's disease because this condition is characterized by hyperthyroidism caused by an autoimmune response leading to the overproduction of thyroid hormones. The use of radioactive iodine therapy exploits the thyroid gland's ability to uptake iodine. When administered, the radioactive iodine is absorbed by thyroid tissue, which effectively destroys hyperactive thyroid cells, thereby reducing hormone production and alleviating the symptoms of hyperthyroidism.

In contrast, subacute thyroiditis is typically a self-limiting inflammatory condition often caused by viral infections, and management is usually supportive, focusing on pain relief rather than iodine treatment. Hashimoto's thyroiditis is an autoimmune disorder that typically leads to hypothyroidism, and radioactive iodine therapy is not indicated as it may worsen the condition by further damaging the thyroid tissue that is already compromised. Papillary thyroid carcinoma may require a different approach, such as surgical resection or radioactive iodine treatment for ablative purposes post-surgery, but it is not primarily treated with radioactive iodine as the first-line approach. Thus, the targeted therapy of radioactive iodine for hyperthyroidism makes it the preferred option for treating Grave's disease.