Revised 2015

Radioactive iodine has been taken by mouth for the treatment of thyroid disorders for over 70 years.

When is radioactive iodine used in the treatment of non- cancerous thyroid disorders?

  • To treat an over-active thyroid gland
  • To reduce thyroid activity caused by nodules
  • To shrink an enlarged thyroid
  • When an over-active thyroid gland due to Graves’ disease fails to settle after antithyroid medication
  • As a first-line therapy in Graves’ disease as an alternative to surgery or antithyroid drug therapy


  • It is now usually given as a capsule, taken with water
  • Antithyroid tablets should be stopped at least one week before and after treatment

Are there any side effects?

  • Long-term - hypothyroidism (under-active thyroid) may develop in 50-90% of people as an expected consequence of treatment
  • Short-term - rarely, some soreness around the thyroid gland
  • Existing thyroid eye disease may worsen, particularly if the eyes are currently sore or inflamed

Is radioactive iodine treatment safe?

  • Studies show there is no increased risk of thyroid or other cancers
  • It should not be given to pregnant women or women who are breast-feeding
  • Men should avoid fathering a child for four months, and women should avoid conceiving for six months, after radioactive iodine treatment
  • Fertility for both men and women is not affected
  • Avoid close contact with babies, children under six years and pregnant women and pets for two to three weeks or as advised by your clinical team


  • Blood tests are usually carried out within 4–6 weeks of the treatment, then repeated every 1-3 months until stable within the first 12 months after treatment
  • Once a year thereafter
  • Sometimes a second dose of radioiodine is needed (approximately 1 in 20)
  • There are no problems with having a follow-up dose

It is well recognised that thyroid problems often run in families and if family members are unwell they should be encouraged to discuss with their own GP whether thyroid testing is warranted.

If you have questions or concerns about your thyroid disorder, you should talk to your doctor or specialist as they will be best placed to advise you. You may also contact the British Thyroid Foundation for further information and support, or if you have any comments about the information contained in this leaflet.

The British Thyroid Foundation
The British Thyroid Foundation is a registered charity: England and Wales No 1006391, Scotland SC046037

Membership Information
Quick Guides

Endorsed by:

The British Thyroid Association - medical professionals encouraging the highest standards in patient care and research

The British Association of Endocrine and Thyroid Surgeons - the representative body of British surgeons who have a specialist interest in surgery of the endocrine glands (thyroid, parathyroid and adrenal)

First issued: 2008
Revised: 2010, 2011, 2015
Our literature is reviewed every two years and revised if necessary.

logo 400