Radioactive iodine (RAI)

Radioactive iodine (RAI, or radioiodine, or I-131) is a treatment for hyperthyroidism and thyroid cancer that exploits the thyroid's unique ability to absorb iodine from the blood.

When a dose of radioactive I-131 is swallowed, the thyroid absorbs it just as it would ordinary iodine. The radiation then destroys overactive or cancerous thyroid cells largely from within, while limiting damage to surrounding tissue.

For hyperthyroidism (most commonly Graves' disease or toxic nodular goitre), RAI shrinks and reduces the thyroid's hormone output over several months. Many people eventually develop hypothyroidism after RAI and require lifelong levothyroxine - this is an expected and manageable outcome, not a complication.

After RAI, isolation precautions are required for a period (typically days to about a week) to protect others - especially children and pregnant women - from radiation exposure. The exact duration depends on the dose. Your nuclear medicine team will provide specific written guidance. RAI is generally not recommended during pregnancy or breastfeeding.