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Thyrotoxicosis and its treatment with radioiodine

Here are the answers to some common questions thyrotoxicosis and its treatment with radioiodine.

What is thyrotoxicosis?

This is a term used to describe a condition where the thyroid gland is overactive and producing too much thyroid hormone (thyroxin). If not treated your health will be affected.

What is radioiodine treatment?

This uses a form of iodine that is radioactive. The thyroid absorbs iodine obtained from your diet to perform its normal function, which is to produce thyroxin. Radioactive iodine will concentrate in the same way as normal iodine but will cause the thyroid to produce less thyroxin. This is a common and well accepted form of treatment that has been used worldwide for more than 50 years.

How is the treatment given?

By swallowing a small gelatine capsule (the size of an antibiotic capsule) containing the radioiodine. This will not make you feel unwell and you may leave the hospital immediately following treatment.
You may eat and drink normally before attending for treatment but we ask that you do not eat or drink anything for two hours after treatment. This will help you to absorb the radioiodine more quickly.

How long should I stay away from work?

You can return to work immediately unless your job involves:

  • handling food
  • working in close proximity to the same individual for most of the working day
  • working with young children

If you fall into one of these categories you must inform the hospital staff when you come for your treatment, so that they can advise you on when to return to work.

Can radioiodine cause cancer?

No. Radioiodine has been used successfully for the treatment of thyrotoxicosis for more than 50 years. Patients who have received this treatment have been studied very carefully. There is no increased risk of you developing cancer as a result of this treatment.

Are there any risks in having children?

No. 50 years of experience with radioiodine shows that there is no effect on the health of children of patients who have received radioiodine. However we do ask that you avoid pregnancy, breast feeding or fathering children for the four months following treatment.

Are there any long-term effects?

Radioiodine may result in your thyroid becoming underactive. This could happen in a few months or even years. Your doctor will arrange for you to have regular blood tests to detect this. Underactivity of the thyroid is easily treated with the natural thyroid hormone thyroxin, which is very safe.   

How many treatments will I need?

One is usually sufficient. However in about a third of patients one capsule proves insufficient and your doctor may advise you to take a second capsule.

How quick will the radioiodine work?

The effects are gradual over the next few weeks.

What about my tablets?

It is usual for your doctor to stop your thyroid tablets for a short while prior to treatment. This is to allow the radioiodine a better chance of working. You may be advised to restart these tablets a few days following treatment. This will benefit you while the radioiodine is beginning to work.

How long will the radioiodine stay in my body?

Only temporarily. Most will be accumulated by your thyroid over the next two to three days. We ask that you drink plenty of fluids during this time. The rest will be passed from your body in urine with a tiny amount leaving in saliva and perspiration.

Is there any danger to my family?

No. But to avoid any unnecessary radiation to your family you will be given a set of precautions to follow when you return home. These will be given to you in writing in an "Instruction Card" and must be observed until the date specified in the card. You must keep this card with you until the date specified.

What are these precautions?

The precautions given to you will depend on your personal circumstances and will be discussed with you prior to treatment. They may take the following form:

  • Avoid journeys exceeding one hour on public transport
  • Avoid visiting places of entertainment or places that you know are likely to be crowded
  • Sleep apart from your partner
  • Wear kitchen gloves when preparing food for other individuals
  • Stay away from work
  • Minimise and preferably avoid non-essential close contact with young children and pregnant women

Your doctor will advise you which precautions you will need to take and for how long you will need to follow them.

If you you wish to discuss any particular problems or concerns, please contact the Nuclear Medicine Department on:

If you have any other questions regarding radioiodine treatment please make a note and we will answer them when you attend the hospital.

Last reviewed: 14 June 2023