Q. Five years ago, we were given potassium iodide pills because we live near a nuclear power plant. Are the pills still good?

A. There is no reason to assume that the pills have spoiled or deteriorated, unless they were improperly stored. Like all over-the-counter drugs, potassium iodide pills are labeled with an expiration date, usually five or six years after manufacture.

But their components are very stable, according to the Nuclear Regulatory Commission , and it is safe to take them after the expiration date.

Potassium iodide protects one organ from one kind of radioactive exposure. It prevents the thyroid gland from taking up radioactive forms of iodine that may be released in the event of a Chernobyl-type accident.

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Ingesting or breathing radioactive iodine presents serious long-term risks, including thyroid cancer. Potassium iodide shields the thyroid by saturating it with so much iodine that it can absorb no more.