Radioactive iodine may be discharged into the environment in some radiation events, such as nuclear power plant accidents, and enter the body by inhalation or ingestion. This is known as internal contamination. High quantities of radioactive iodine absorbed by the thyroid can raise the risk of thyroid cancer in newborns, children, and youths for many years following exposure.
Iodine Thyroid Blocking (ITB) should only be taken if public health or emergency response professionals, or a healthcare provider, instructs to. ITB has the potential to be damaging to one’s health. ITB is only useful for certain groups of people in specific circumstances.
Iodine Thyroid Blocking (ITB) should not be considered a stand-alone protective action. A comprehensive public protection strategy covering all urgent and early protective actions, as well as other response actions, including evacuation and sheltering, restriction on consuming contaminated food, milk and drinking water, should be developed as per the IAEA’s general safety requirements and its supporting safety guide.
The optimal period of administration of stable iodine is less than 24 hours prior to, and up to two hours after, the expected onset of exposure. It would still be reasonable to administer (ITB) up to eight hours after the estimated onset of exposure. However, starting with ITB later than 24 hours following exposure may yield more harm than benefit since it would prolong the biological half-life of radioactive iodine that has accumulated in the thyroid.
A single administration of stable iodine is usually sufficient. However, in the case of prolonged (beyond 24 hours) or repeated exposure, unavoidable ingestion of contaminated food and drinking water, and where evacuation is not feasible, repeated administration of stable may be necessary. Neonates, pregnant and breastfeeding women and older adults (over 60 years), should not receive repeated ITB.
Iodine thyroid blocking (ITB) can be hazardous to one’s health and may induce allergic responses. When ITB is not taken exactly as advised by a physician or public health expert, the risk of harm increases.
Harmful health effects may include:
- Gastro-intestinal (stomach) upset, rashes, and inflammation of the salivary glands.
- Allergic reaction.
- The development of hypothyroidism in infants less than one month old who receive more than one dose of ITB.
- Severe illness or death in people who take more ITB than recommended (lethal adult dose of free iodine is 2 to 4 g).
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