Before radioactive iodine

This guide is about preparing, not deciding

Radioactive iodine (RAI, or I-131) is one of several treatment options for hyperthyroidism and is also used after thyroid surgery for certain cancers. Whether RAI is the right choice for you is a decision to make with your specialist team. This guide is for people who have already made that decision and are getting ready for the treatment.

What to expect on the day

RAI is usually given as a single capsule or drink in a nuclear medicine department. The appointment itself is brief - the treatment is over quickly. What comes after requires more planning: because your body temporarily emits low-level radiation, you'll need to follow isolation precautions for a period of days, sometimes longer depending on the dose.

Your nuclear medicine team will provide specific written instructions for your dose. Follow their guidance precisely - it is tailored to you.

Practical preparation checklist

• Diet before treatment: your team may ask you to follow a low-iodine diet in the weeks before RAI, to help the thyroid absorb the treatment more effectively. If so, follow their specific instructions - see iodine: not more-is-better for general background on dietary iodine. Do not start a restricted diet without your team's guidance.
• Medicines: some medications need to be paused before RAI (antithyroid drugs such as carbimazole are typically stopped a number of days beforehand). Your team will tell you exactly what to do and when.
• Contraception: RAI is not safe during pregnancy. Both women and men are advised to avoid conceiving for a period after treatment - the NHS advises at least 6 months for women and at least 4 months for men, though this differs by dose and individual. Your team will confirm exactly how long effective contraception is needed.
• Breastfeeding: RAI is not compatible with breastfeeding. If you are breastfeeding, this must be discussed with your team well in advance.
• Planning for isolation: arrange your home and commitments before treatment day. You will need to minimise close contact with others - especially children under 16 and pregnant women - for the period your team specifies.
• Work and travel: check with your team whether your work involves contact with children or pregnant colleagues, as you may need to discuss specific precautions. International air travel may trigger radiation detectors - ask your team for a letter to carry.

Setting up your isolation period

Full isolation after RAI is usually measured in days, but it varies with dose - and restrictions on close contact with young children and pregnant women can last longer, sometimes a couple of weeks or more. Your team will give you a specific end date or criteria for each precaution. In that period, you'll typically need to:

• Sleep separately from a partner
• Avoid prolonged close contact with children and pregnant women
• Use separate towels and flush the toilet twice after use
• Avoid preparing food for others
• Stay away from crowded public spaces

Have everything you need at home before you go in for treatment - food, supplies, anything to keep you occupied.

Questions to ask your nuclear medicine team

Write these down before your appointment:

• What dose am I receiving, and what does that mean for my isolation period?
• Exactly how long do I need to avoid close contact with children and pregnant women?
• Do I need to follow a low-iodine diet beforehand, and for how long?
• Which of my medicines do I need to stop, and when do I restart them?
• When should I expect levothyroxine to be started or adjusted?
• What are the likely outcomes - and what are the chances I'll develop hypothyroidism?
• How long before we know whether the treatment has worked, and how will that be monitored?
• Are there any effects on thyroid eye disease I should know about?
• What should I do if I feel unwell during the isolation period?
• Is there a contact number for questions after treatment?
• What are the long-term follow-up arrangements?

Thyroid eye disease: a specific question

If you have or have had thyroid eye disease (TED), it's important to discuss this specifically before RAI. There is evidence that RAI can sometimes trigger or worsen TED, particularly in people who smoke or have active eye disease. Your team may recommend a course of steroids around the time of treatment, or may advise a different treatment approach. This is not a reason to avoid asking the question - it's a reason to ask it.

After treatment: when to contact your team

Most people tolerate RAI well. Contact your team if:

• You experience significant neck pain or swelling (radiation thyroiditis can occur in the days after treatment)
• You feel very unwell or have a high temperature
• You have questions about isolation precautions during the period

If you're ever unsure during the isolation period, call your nuclear medicine team rather than attend A&E - so that any radiation precautions can be planned for.

More resources

See radioactive iodine explained for background on how the treatment works. The questions tool can help you organise what to ask before your appointment. For dietary iodine background, see iodine: not more-is-better.