Radioactive iodine for thyroid cancer
Radioactive iodine treatment is a type of radioisotope therapy. It is a useful treatment for some types of thyroid cancer.
The thyroid gland absorbs and stores most of the iodine in your body. It gets iodine from certain foods and uses this to make essential thyroid hormones.
Radioactive iodine treatment uses a radioactive form of iodine called iodine 131 (I-131). It travels through your bloodstream and is taken up by thyroid cells and thyroid cancer cells. This is because these cells can absorb iodine.
The radioactive iodine gives these cells a high dose of radiation. This damages and destroys the thyroid cells and any cancer cells.
Other cells in the body absorb much less iodine, so they receive a much lower dose of radiation.
Read more about radioisotope therapy
Radioactive iodine is only suitable for some types of thyroid cancer. This includes follicular and papillary thyroid cancer. Thyroid cancer cells can pick up radioactive iodine, even if they have spread to other parts of the body. So it can be a treatment for thyroid cancer that has spread.
But radioactive iodine might not be necessary or suitable for everyone with these types of thyroid cancer. Not all cancer cells take up the iodine. You might have a test dose to see if your cancer cells do.
You might have radioactive iodine treatment:
after surgery, to kill any cancer cells that may have been left behind
to treat thyroid cancer that has spread
to treat thyroid cancer that has come back after treatment
You may only need to have this treatment once. But you can repeat it if needed, until there is no sign of any thyroid cancer on your scans. Your doctor will discuss this with you.
For radioactive iodine treatment to work, your thyroid cancer cells need to take up the radioactive iodine. A high level of thyroid stimulating hormone (TSH) helps thyroid cells take up iodine.
To increase your TSH levels, your doctor will give you an injection of a man-made TSH called recombinant human TSH (rhTSH). You have it once a day for 2 days.
Occasionally your doctor may ask you to stop taking your thyroid hormone tablets a few weeks before treatment. But this is much less common. Doctors call this thyroid hormone withdrawal.
Your healthcare team will explain what you need to do and what is going to happen. They will also let you know when to re-start your hormone tablets if you stopped taking them.
A low iodine diet means avoiding foods that have a high level of iodine in them.
You might need to have a low iodine diet for 1 to 2 weeks before your treatment. This diet reduces the amount of iodine in your body. And prepares the thyroid cells and cancer cells so that they can absorb the radioactive iodine.
Most foods and drinks contain some iodine. Below is the British Thyroid Foundation’s list of what foods you can and cannot eat on a low iodine diet:
You can eat the following foods because they contain very low levels of iodine:
fresh and frozen fruit
fresh and frozen vegetables
fresh and frozen meats
potatoes
bread
rice
dried pasta
pulses and grains
plain fats and oils which are non dairy – this includes olive oil spread
soft drinks, fruit juices, tea and coffee
dark chocolate
You should try not to eat these foods as they have high levels of iodine:
seaweed, including kelp supplements
seafood and fish
cow’s and goat’s milk, including organic cow’s milk
cheese, ice cream, yoghurt and butter
plant based alternatives to milk such as oat, soya or almond milks that have added iodine
eggs and egg yolks
fresh pasta which is made with eggs
cakes and biscuits containing eggs and dairy fats or butter
soy products such as soy sauce, soy milk and tofu
multivitamin, mineral supplements and some cough mixtures that contain iodine
milk and white chocolate
Table salt and sea salt with no added iodine can be used but avoid having too much. If you have beer and wine then drink within the general recommendations for healthy drinking. Do not stop taking your regular medicines or supplements without speaking to your healthcare team.
You can return to your normal diet two hours after you have had your treatment.
It is unlikely to affect your treatment if you eat high iodine food by mistake. If you do, just carry on with the low iodine diet.
Speak to your healthcare team if you are following a special diet for a health condition such as or . They can help you with this.
Tell your doctor if you think you may be pregnant. You should not have this treatment during pregnancy.
Talk to your doctor if you are breastfeeding. You will need to stop breastfeeding at least 8 weeks before you have treatment with radioactive iodine. You will not be able to breastfeed again until you have another pregnancy.
For this treatment you will be . To keep others safe around you, you will need to isolate in a room at the hospital on your own.
This means you will need to be able to care for yourself during that time. Hospital staff will not be able to enter the room and help you. This is usually for a few days.
Your healthcare team will talk to you about any concerns you have about this. They will also tell you what to expect during your stay, and help you plan what to bring into hospital with you.
Last reviewed: 08 Oct 2026
Next review due: 08 Oct 2029
You have radioactive iodine treatment in the hospital. You usually stay in for a few days.
Your healthcare team will tell you about any safety precautions you need to follow after your radioactive iodine treatment.
Doctors will arrange for you to have tests and scans at regular follow up appointments.
There are people who can help and things you can do to help cope with a diagnosis of thyroid cancer.
Radioisotope therapy uses radioactive medicines to treat some types of cancer. It is also known as radionuclide therapy. You have the radioisotope as a drink, capsule or injection.
The thyroid is a small butterfly shaped gland that makes and releases hormones. It’s found at the front of your neck in the lowest part.
