Radioactive Iodine (I-131) Therapy
Radioactive iodine (I-131) therapy uses a small dose of radioactive iodine, swallowed as a capsule or drink, that is absorbed by thyroid tissue and destroys it from within. It is used after surgery for differentiated thyroid cancer to clear any remaining or microscopic disease, and to calm an overactive thyroid gland.
Medically reviewed by the Florence Healthcare medical team · Last reviewed June 2026
Overview
Radioactive iodine therapy takes advantage of a simple fact: thyroid cells absorb iodine wherever they are in the body. The patient swallows a measured dose of iodine-131 as a capsule or drink, and the thyroid tissue takes it up and is destroyed by short-range radiation, while the rest of the body is largely spared. It is most often given after surgery for differentiated (papillary or follicular) thyroid cancer to remove any remnant or microscopic disease, and as a treatment for an overactive thyroid (hyperthyroidism). Because the body briefly emits low-level radiation, a short stay in a dedicated room with radiation-protection precautions is needed. The dose is planned and delivered by the nuclear medicine team.
International patients are supported by a dedicated coordinator who arranges scheduling, the isolation room and aftercare. Our specialists can review your records and prior pathology remotely to give a second opinion before you travel, and you receive a transparent, itemized cost estimate in advance.
Who is a candidate?
- People treated surgically for differentiated thyroid cancer who need remnant tissue or microscopic disease cleared
- Patients with an overactive thyroid (hyperthyroidism), including Graves' disease or toxic nodules
- Those whose specialist has confirmed the tumor or gland takes up iodine and would respond to treatment
- Patients able to follow a short low-iodine diet and brief radiation-protection precautions
- People who are not pregnant or breastfeeding, as radioactive iodine is unsafe in these situations
- Patients whose case has been reviewed by the nuclear medicine and endocrine team as appropriate for I-131
What happens
- 1
Preparation
For a few days to a couple of weeks beforehand you may follow a low-iodine diet and either stop thyroid hormone or receive injections to raise the hormone that makes thyroid tissue absorb iodine. Your team confirms you are not pregnant and explains every step.
- 2
During treatment
You swallow the iodine-131 as a single capsule or drink — there is no surgery and no anesthesia. You then stay in a dedicated room with radiation-protection precautions for a short period while the low-level radiation your body emits falls to a safe level.
- 3
Afterwards & results
Once levels are safe you are discharged with simple contact precautions to follow at home for a few days. A scan may check where the iodine was taken up, and follow-up blood tests and imaging confirm the effect. Your coordinator arranges aftercare and remote follow-up once you return home.
Benefits
- Targets thyroid tissue specifically, largely sparing the rest of the body
- Given by mouth as a capsule or drink — no surgery, incisions or anesthesia
- Effective at clearing remnant or microscopic thyroid cancer after surgery
- A well-established, long-used treatment for an overactive thyroid
- Lowers the chance of thyroid cancer returning and makes later follow-up more reliable
Risks & considerations
- Temporary dry mouth, altered taste, or tenderness of the salivary glands or neck
- Mild short-term nausea, and the need to follow brief radiation-protection precautions at home
- Treatment for an overactive thyroid often leaves the gland underactive, needing lifelong hormone tablets
- Not safe during pregnancy or breastfeeding; men and women are advised to delay conception for a period afterwards
Conditions this treats
Where it is performed
This procedure is delivered by our Nuclear Medicine & Theranostics Department.
Learn more before you decide
Provider-reviewed guides on the related conditions, symptoms and tests in our Health Library.
Radioactive Iodine (I-131) Therapy — frequently asked questions
For a short time your body emits low-level radiation, which is why you stay in a dedicated room until levels are safe. After discharge you follow simple precautions for a few days — such as keeping a little distance from young children and pregnant women — which your team explains clearly.
A low-iodine diet and raising the hormone that stimulates thyroid tissue make any remaining thyroid cells 'hungry' for iodine, so they absorb more of the radioactive dose and treatment works better. Your team gives you a simple plan to follow.
No. You simply swallow a capsule or drink — there is no surgery, no injection into a vein and no anesthesia. Any side effects, such as a dry mouth or mild nausea, are usually short-lived.
Yes. Share your pathology, blood tests and imaging and our nuclear medicine and endocrine specialists provide an independent opinion on whether radioactive iodine is appropriate and what dose suits you, before you commit to travel.
Most patients need a short stay covering preparation, the isolation period and discharge checks — your coordinator confirms the exact timeline. We provide a transparent, itemized cost estimate after reviewing your case, listing the dose, the dedicated room, scans and follow-up. We do not quote fixed prices online because each plan is individual.
Often, yes. After cancer treatment you usually take thyroid hormone tablets, and treatment for an overactive thyroid commonly leaves the gland underactive, which is easily managed with daily hormone replacement and monitoring.
Related treatments
Considering radioactive iodine (i-131) therapy?
Share your reports for a medical second opinion and a transparent, itemized cost estimate — usually within 48 hours.