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I-131 Thyroid Therapy

I-131 Thyroid Therapy uses a radioactive medicine to treat overactive thyroid tissue (Hyperthyroidism) or certain types of thyroid cancers.


Your child will be asked to stop all food and drink 2 hours before therapy and continue to fast for 1 more hour after receiving the medicine by mouth. 

Your child’s doctor will ask you to have bloodwork done within 1 week of coming for the therapy.

Your child will be asked to change their diet and stop certain medications, cough syrups and vitamins before coming in for the therapy.  Please refer to the following guidelines:

  • Your child will need to stop taking thyroid medications before the test. Your child’s doctor will let you know when to stop certain medications. This can be anywhere from 1 to 6 weeks before the test so it is important to check with your child’s doctor.
  • Stop multivitamins for 4 weeks before the test
  • Stop cough medicines 48 hours before the test
  • Your child will be asked to go on a low iodine diet 1 week before the test. Including:
    • Do not eat fish, shellfish or other sea-based foods
    • Do not eat foods with a lot of iodized salt or sea salt
  • No other test (for example, CT, MRI or Xray) where your child received contrast though IV or to drink for 6 weeks before the appointment.

What to expect

The procedure will take up to 30 minutes. Your child should only be accompanied by 1 parent or guardian for this therapy.  Siblings are not allowed in the room during the therapy.  Eating and drinking are not allowed in the room.

Your child will be given a radioactive medicine containing iodine by mouth.   A nuclear medicine physician and radiation safety specialist will review radiation safety guidelines that will need to be followed for 7 days after receiving the therapy.

Post test

Thorough radiation safety guidelines will be reviewed with you and your child and must be followed for 7 days following the therapy.  You will be asked to sign these guidelines and will be given a copy for reference.

Please call the Nuclear Medicine Department at 416-813-6065 if you have any questions about the procedure or if you need to change the appointment.

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