I-131 radioactive iodine pill: what to know

I-131 is a radioactive form of iodine taken by mouth as a capsule or liquid. Thyroid cells naturally use iodine, so the material can concentrate in thyroid tissue. The radiation then acts locally in cells that absorb it, while the body gradually clears unused material.

The treatment plan depends on your diagnosis, thyroid function, previous surgery and the goal of treatment. A nuclear medicine team gives the dose and explains how long radiation-safety measures apply.

Follow the team’s instructions about thyroid medicine, diet and pregnancy testing. Tell them if you are pregnant, breastfeeding, taking iodine-containing products or have kidney problems. After taking the pill, drink fluids as advised and wash your hands carefully after using the toilet.

You may need to limit close contact for a period set by the specialist, especially with children and pregnant people. Use separate personal items if instructed, and do not travel or return to work until the team says it is suitable.

Call the treatment team for persistent vomiting, difficulty swallowing, marked neck swelling, severe mouth or throat pain, or symptoms that prevent you from drinking. Seek emergency help for trouble breathing, collapse or a severe allergic reaction.

Ask what the pill is intended to do, which medicines to pause, how long precautions last, how follow-up will measure the response, and whom to contact after hours.