Radioactive Iodine Therapy

Radioactive iodine therapy, also called I-131 therapy, is a treatment taken by mouth as a capsule or liquid. Thyroid cells naturally absorb iodine, so I-131 can deliver radiation from inside the body to thyroid tissue and some thyroid cancer cells. Most of the unused iodine leaves through urine, with smaller amounts leaving through saliva and sweat.

Your team may ask you to follow a low-iodine diet for a short period and may adjust thyroid hormone medicine so the remaining thyroid cells take up the treatment. A blood test or injection can help stimulate uptake. On treatment day, you swallow the prescribed dose in a controlled setting. Radiation-safety instructions then guide distance, hygiene, childcare, work, travel, and sleeping arrangements.

Short-term effects can include a dry or sore mouth, altered taste, nausea, neck tenderness, and swelling near the thyroid bed. Salivary-gland irritation may cause jaw discomfort or dry eyes. Rare but serious concerns include severe neck swelling or breathing difficulty, which require urgent medical help. Your team gives specific precautions because the dose and your living arrangements affect radiation protection.

The expected benefit depends on the thyroid cancer type, tumour size and spread, iodine uptake, surgery results, and the treatment goal. I-131 may destroy remaining thyroid tissue or treat iodine-avid disease after surgery. Follow-up blood tests and scans help show how the disease is responding. Results cannot be guaranteed, and some cancers do not absorb iodine well.

Treatment is selective because iodine-absorbing thyroid cells concentrate I-131. Radiation precautions are temporary but must be followed exactly. Pregnancy and breastfeeding require special planning, and pregnancy should be avoided for the interval advised by your nuclear-medicine team. Thyroid hormone replacement may be needed after treatment.

Specialists may recommend radioactive iodine for selected differentiated thyroid cancers after thyroid surgery, especially when remaining thyroid tissue or iodine-absorbing cancer cells need treatment. It is not useful for every thyroid cancer. Read more about [Thyroid Cancer](/conditions/thyroid-cancer/) and the treatment material [Radioactive Iodine (I-131)](/materials/radioactive-iodine-i131/).

Care commonly includes confirming the diagnosis and treatment goal, preparing the body for iodine uptake, taking the dose, following radiation-safety instructions, and returning for planned blood tests or imaging. The nuclear-medicine team tells you when restrictions end and how to manage medicines at home.

Many people return home with written radiation precautions, while some doses require a period in a specialist room. Drink fluids if permitted, follow the hygiene instructions, and plan help with household tasks if close contact must be limited. Dry mouth or taste changes can linger, and follow-up may continue with hormone tests, scans, and specialist reviews.

Tell the team about pregnancy, breastfeeding, kidney problems, medicines, and difficulty following isolation instructions before treatment. Seek urgent help for breathing difficulty or rapidly increasing neck swelling. Report persistent dry mouth, eye discomfort, or troublesome nausea so your clinicians can advise supportive care.

Depending on the cancer and its spread, care may involve surgery such as [Thyroid Removal Surgery](/treatments/surgical-oncology/thyroidectomy/), active surveillance, external-beam radiotherapy, targeted medicines, or other systemic treatment. Your multidisciplinary team matches treatment to the tumour’s biology and your health.

Choose a service with endocrinology, nuclear medicine, oncology, laboratory, and imaging support. Ask who will provide the dose, what home precautions apply, how medicines will change, when you can resume close contact, and which symptoms should prompt a call.