Radioactive Iodine Therapy
Radioactive iodine (RAI) therapy uses I-131 — a radioactive form of iodine the thyroid naturally absorbs — to treat overactive thyroid tissue or thyroid cancer.
It is a well-established, targeted treatment with a long safety record.
Last medically reviewed: 1 November 2025
Key points
- Radioactive iodine is taken up by thyroid tissue.
- It is used for hyperthyroidism and selected thyroid cancers.
- It often leads to hypothyroidism, treated with levothyroxine.
- Pregnancy and breastfeeding are contraindications.
How it works
The thyroid uniquely absorbs iodine to make hormone. Radioactive iodine concentrates in thyroid tissue and destroys it with targeted radiation — sparing surrounding tissues almost entirely.
For hyperthyroidism, the goal is to reduce function to normal or underactive (managed with levothyroxine). For thyroid cancer, higher doses target residual cancer cells.
Who it suits
RAI is a standard option for Graves’ disease relapse, toxic nodular goitre, and recurrent hyperthyroidism. For thyroid cancer, it is used selectively for higher-risk differentiated cancers.
It is less preferred in pregnancy, breastfeeding, and moderate-to-severe active thyroid eye disease (may worsen orbitopathy).
Precautions and recovery
After treatment, patients may need to avoid close contact with pregnant women and young children briefly — radiation safety precautions depend on dose. Salivary glands may be mildly affected; staying hydrated helps.
Hypothyroidism is a common outcome — expected and easily managed with levothyroxine. Thyroid function is monitored regularly afterward.
Frequently asked questions
Is radioactive iodine safe?
Yes — it has been used for over 80 years with a strong safety record. The radiation is targeted to thyroid tissue; precautions minimize exposure to others.
Will I become hypothyroid after RAI?
Very likely for hyperthyroidism treatment — this is expected and managed with levothyroxine. For cancer treatment, hypothyroidism is often deliberately induced first.
Can I have RAI if I have eye disease?
RAI can potentially worsen active Graves’ orbitopathy — surgery or antithyroid drugs may be preferred when eye disease is significant.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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