Which of the following treatments may lead to hypothyroidism if used long-term?

Radioactive iodine therapy is a treatment often used for conditions such as hyperthyroidism and certain types of thyroid cancer. This therapy works by damaging the cells in the thyroid gland to reduce its function or destroy it. When used long-term, or even in a single large dose, it can lead to an underactive thyroid, or hypothyroidism, as the thyroid may be unable to produce sufficient hormones after a significant reduction in its cell number or function.

In contrast, beta-blockers are primarily used for cardiovascular issues and do not directly affect thyroid hormone production. Antithyroid medications, while effective in treating hyperthyroidism by inhibiting hormone synthesis, can lead to a state of euthyroidism rather than directly causing hypothyroidism when used appropriately. Hormone replacement therapy is specifically designed to replace deficient hormones and would not cause hypothyroidism; rather, it aims to correct insufficiencies. Thus, long-term radioactive iodine therapy is identified as the treatment that may lead to hypothyroidism due to its impact on thyroid function.