How does radioactive iodine therapy work?

The treatment is usually swallowed as a capsule or liquid containing [Radioactive Iodine (I-131)](/materials/radioactive-iodine-i131/). Thyroid cells naturally take up iodine, so the radioactive form concentrates in thyroid tissue and releases radiation there. The radiation damages the cells that absorb it. For [Thyroid Cancer](/conditions/thyroid-cancer/), treatment may be considered after [Thyroid Removal Surgery](/treatments/surgical-oncology/thyroidectomy/) when the clinical team believes remaining thyroid tissue should be treated. The treatment plan depends on the type and extent of disease, thyroid function and other health factors.

Follow the nuclear medicine team’s instructions about food, medicines and timing. After treatment, your body releases small amounts of radiation through urine, saliva and sweat for a period set by the team. Follow their specific advice about distance from others, sleeping arrangements, childcare, travel, handwashing and toilet hygiene. Drink fluids if permitted, and do not share personal items when instructed. Tell the team if you are pregnant, breastfeeding or caring for a young child.

Contact your treatment team for severe neck swelling, trouble swallowing, breathing difficulty, persistent vomiting or symptoms of dehydration. Seek emergency care for major breathing difficulty or collapse. Report troublesome dry mouth, mouth soreness, neck pain or changes in salivary glands, because supportive treatment may help.

Ask why I-131 is recommended, how to prepare, how long radiation-safety precautions will last, and which symptoms need a call. Discuss follow-up blood tests, thyroid hormone replacement and how the treatment fits with surgery or other care.