Radioactive iodine for 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.
You have radioactive iodine as a capsule which you swallow. The capsule is about the size of a paracetamol tablet. Rarely, you might have radioactive iodine as a drip into your bloodstream (intravenously) or as a drink. This is very uncommon.
You won’t be able to eat or drink for a couple of hours afterwards so that your body can absorb the iodine. After that, you should drink plenty of fluids to flush the radioactive iodine out of your system. You can then eat as normal and do not need to follow the low iodine diet.
The treatment makes you radioactive. So your sweat, pee and saliva will be radioactive for a few days. You will have to be alone during this time, usually in a hospital room. This means you will be in isolation.
There are certain precautions that you and the staff need to follow. Try not to worry about these. Your treatment contains a low dose of radiation that is necessary to treat your cancer.
Your team may use a radiation monitor (Geiger counter) to check your levels of radioactivity or test anything you take out of your room.
They may serve your meals on disposable plates with disposable cutlery. You put these in a special bin when you have finished with them.
The hospital staff ask you to flush the toilet more than once after you have used it and to shower at least once every day.
Being in a room on your own protects other people from radiation. Visitors should be kept to a minimum. Your team will not allow pregnant women and children to visit you. Other visitors may be able to visit you for a short time when it is safe for them to do so. They will have to stay a distance from you or even be outside the room when visiting.
Staff come into your room for a limited amount of time. They stay at a safe distance from you and can only stay in your room with you for as long as is necessary. This is because they will care for many people who have this treatment. So their exposure to radiaiton is carefully controlled. It is important that you know that you are not at any risk from the radiation.
Being alone in a single room can feel lonely. Some people find it frightening. It can help to talk to the nurses about your worries. They can reassure you.
You may be able to take a few personal possessions into your room. The hospital staff will tell you if this is possible and what you can have with you. They may suggest not bringing too many items in and nothing of value. When you are ready to go home, you may need to leave some of your things behind until they don’t have any radiation on them.
Some hospital rooms will have a television and a phone. You could check before you go in to find out if this is the case.
Last reviewed: 08 Oct 2026
Next review due: 08 Oct 2029
You might need to have a low iodine diet for a few weeks before you have your treatment. Your thyroid stimulating hormone levels also need to be high before treatment.
Your healthcare team will tell you about any safety precautions you need to follow after your radioactive iodine treatment.
There are people who can help and things you can do to help cope with a diagnosis of thyroid cancer.
Doctors will arrange for you to have tests and scans at regular follow up appointments.
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.
