We’ve gotten some questions asking for clarification about our statement on potassium-iodide (KI) pills. In particular, why are KI pills effective in the case of inhalation of radioactive iodine, but not considered an effective countermeasure to ingesting it via, for example, milk?
According to the 2004 National Academy of Sciences study on Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident:
Exposure to radioactive iodine is possible through the ingestion pathway, so it is important that plans address this situation. Monitoring of the environment and food products controls this route of exposure. Removing contaminated products from the market and isolating contaminated products until the radioactive iodine decays to safe levels are the most effective way to eliminate radiation exposure and damage to the thyroid. That also eliminates the need for the use of KI by the general public as a protective action.
Potassium iodide can only reduce the risk from radioactive iodine that has entered the body, not eliminate it. People in the radioactive plume do not have the option of not breathing, so taking KI is an effective countermeasure against inhalation. However, people have the option of not drinking contaminated milk or eating other contaminated food products. In comparison, taking KI would be less effective.
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