Radioiodine Treatment – Higher Dose

Radioiodine has been used to treat hyperthyroidism (overactive thyroid) since the 1940’s. It has been shown that for many people it is better than drug therapy and surgery. Your consultant has decided that this is the best way of treating your thyroid gland and they will have discussed this with you in clinic.

How does it work

Your thyroid gland produces hormones which are important in controlling your body’s metabolism. If your thyroid is overactive it produces too much of the thyroid hormone thyroxine. Too much thyroxine can speed up your metabolism and you may experience symptoms such as weight loss, palpitations, tiredness, nervousness and irritability.

To produce thyroxine, your thyroid must take iodine from your bloodstream; in fact most of your body’s iodine is concentrated in your thyroid gland. This means when you are given radioiodine, most of it is quickly taken up into your thyroid. The radioactivity destroys the overactive thyroid tissue which stops it from producing as much thyroxine.

Is there anything I should tell the staff before the scan?

Yes. If you are pregnant or think you may be pregnant, please inform us. We also need to know if you are breastfeeding as you will need to stop breastfeeding for several hours following the scan.

Preparing for Radioiodine

We want your treatment to work as well and as quickly as possible so it is important that you read the following instructions as soon as you can.


As some medication can stop the radioiodine from working properly, your consultant may have asked you to stop taking some medication up to 3 weeks before your appointment. It is important that you follow the instructions that they have given you. If you have not been asked to stop any medication but are currently taking Carbimazole or Propylthiouracil (PTU) please contact the medical physics department (details can be found at the end of the leaflet) for advice.


So that the radioiodine will work as quickly as possible, we need to restrict the amount of iodine in your body for one week before your appointment. This is so that when you are given the radioiodine capsule; your thyroid will absorb it quickly. The majority of your body’s iodine comes from the food you eat so we will need you to follow a special diet.

For seven days before your appointment please do not eat any fish, seafood or seaweed and please limit as much as possible the dairy products you eat and drink. This includes milk, cheese, butter and yoghurt. Please contact us if you are in any doubt about anything you have eaten.

Hospital Scans

If you have had any scans or x-rays which involved the injection of a contrast material (usually a Computed Tomography (CT) scan) within 2 months of your radioiodine appointment, please contact us.

Appointment Day


Do not have anything to eat for five hours before your appointment. You may have a drink (tea, coffee, water etc.) at lunch time or if you need to take any mediation. If you are diabetic, please contact us to make special arrangements.

How long will the appointment last?

Approximately 20 minutes. Before we can give you your treatment there are a number of questions we have to ask you. Some will be relevant to you but others won’t be. We ask everybody the same questions.

If you are aged 55 or younger we have to perform a pregnancy test on all patients before we can proceed to the treatment. If you are pregnant we cannot go ahead with the treatment.

You will have the opportunity to ask any questions you have before you are given the treatment.

How is the radioiodine treatment given?

The treatment is given to you as a small capsule which is swallowed. This capsule is the same size as a regular tablet and you should have no trouble swallowing it. We will give you a drink of water with it. If you think you may not be able to swallow the capsule, please contact us at least 5 days before your appointment.

Can anyone come with me?

Yes. You can have someone accompany you if you wish and they can stay with you during your treatment. However we do ask that you don’t bring children or anyone who is pregnant with you.

Going home

The treatment will have no impact on your ability to drive. If somebody comes with you, you may travel home with them by car for journeys up to three hours as long as you sit in the seat furthest from them and keep at least one arm length from any other passengers.
You can travel home using public transport for journeys up to one hour.

After your treatment

So that your thyroid can begin to absorb the iodine as quickly as possible you should not drink for one hour or eat for two hours after swallowing the capsule.

For the next two days you should stay on your low iodine diet (no seafood and minimal dairy products) to ensure as much of the radioiodine is absorbed as possible.

How long does the treatment take to work?

The treatment takes several weeks to work so you will not notice any improvement in your symptoms straight away. As everybody is different it can be difficult to predict exactly how well the treatment will work for you. It is possible that you may need to return for a second radioiodine capsule if we feel the first treatment has not worked well enough. It could also be possible that the treatment works a little too well and your thyroid becomes underactive. If this happens you will need to take thyroxine tablets daily to maintain your thyroid hormone levels. Your consultant should have discussed this with you. If you have any concerns regarding this please contact your consultant.

You should receive an appointment with your consultant approximately 6 weeks after your radioiodine treatment so that they can check to see how well the treatment has worked.

Radiation precautions

For a few weeks after your treatment your thyroid gland will be slightly radioactive. The amount of radioactivity your thyroid contains will get less every day. While your thyroid contains radioactivity it means you can expose the people around you to radiation. Although the amount of radiation you will expose other people to is very small it is always wise to keep this extra radiation exposure to a minimum. You can reduce the radiation exposure to other people by limiting the amount of time you spend with them and by keeping more than one arm’s length away from them.

Adults you see regularly

For 16 days after your treatment, you should not spend more than a few minutes each day within arm’s reach of any adults you see regularly (for example spouse or partner, relatives, friends or colleagues) You must not share a bed with anyone or sleep within 2 metres of anyone, even if there is a wall between your beds.

People can still come to see you or stay in the same house as you but you should keep at least one arm length from them if they will be with you for longer than a few minutes.

Children and pregnant women

For 27 days after your treatment, you should not spend more than a few minutes each day within arm’s reach of any children or anyone who is pregnant. You must not share a bed with them or sleep within 2 metres of them, even if there is a wall between your beds.

They can still come to see you or stay in the same house as you but you should keep at least one arm length from them if they will be with you for longer than a few minutes.

Can I go back to work?

You can return to work the following day as long as you do not spend more than a few minutes a day within arm’s reach of other people. If you work with radiation sensitive equipment, children, pregnant women or closely with other adults for extended periods you may need to take time off work. Your GP should be able to arrange a sick note for you. If you are in any doubt, please contact us before your appointment to discuss your particular circumstances.

Personal hygiene

Most of the radioactivity is concentrated in your thyroid gland but for a few days after your treatment some of the radioiodine leaves your body in your urine and sweat. Drinking plenty of fluids and emptying your bladder frequently can help speed this up.

Please take care with personal hygiene in the first few days after treatment. Always flush the toilet after use and always wash your hands. You should use your own towels and face cloth. Your clothes do not need to be washed separately unless you experience any incontinence.

Further restrictions

If you are trying to have a baby, men should avoid fathering children for four months after treatment. Women should avoid pregnancy for 6 months after treatment. If you are currently breastfeeding you must stop and will be unable to restart again as the radioiodine is excreted in breastmilk. You must not donate blood for 6 months after your treatment.

If you are planning to go on holiday within 21 days of your treatment please contact us as we may need to postpone your treatment until after your return.

Is the treatment safe?

Large follow-up studies have been carried out for more than 70 years in many European countries and the United States. These show that there is no increased risk of cancer from treatment with radioactive iodine.

Useful information

[1] The British Thyroid Foundation

[2] The British Nuclear Medicine Society

Contact numbers for further advice

Specialist Radiographer/Clinical Technologists
Medical Physics
Tel: (0191) 445 2710
Monday to Friday 8:30am to 4:30pm

Physicist/Head of Medical Physics
Tel: (0191) 445 5516 or (0191) 445 2476
Monday to Friday 9am to 5pm