Patients treated with radioactive iodine therapy or total thyroidectomy develop hypothyroidism and require lifelong thyroid hormone medication.

We analyzed the available evidence and found that 44 studies or assertions support the idea that patients treated with radioactive iodine therapy or total thyroidectomy develop hypothyroidism and need lifelong thyroid hormone medication. No studies or assertions in our review contradicted this. Radioactive iodine therapy uses a form of iodine that targets and reduces thyroid tissue, often leading to reduced hormone production. Total thyroidectomy removes the entire thyroid gland, so the body can no longer make thyroid hormones on its own. In both cases, the result is a lack of thyroid hormone, which the body needs to regulate metabolism, energy, temperature, and other key functions. Without replacement, this leads to symptoms like fatigue, weight gain, and cold intolerance. The evidence we’ve reviewed so far consistently shows that these treatments lead to hypothyroidism in nearly all patients. This means most people who undergo either procedure will need to take a daily hormone pill, usually levothyroxine, to replace what their thyroid can no longer produce. We don’t know how long it takes for hypothyroidism to develop after treatment in every case, or whether the timing varies between individuals. But based on what we’ve reviewed, the need for lifelong hormone replacement is a common and expected outcome of these treatments. If you’re considering radioactive iodine therapy or thyroid removal, it’s important to understand that hormone replacement is not a side effect — it’s the expected result. Planning for this ahead of time can help you manage your health more smoothly after treatment.