Potassium iodide, also known as KI, is a form of iodine. Potassium iodide has been determined by the U.S. Food and Drug Administration (FDA) to be a safe and effective method to block exposure to one product of a nuclear release - radioactive iodine. Radioactive iodine, either inhaled or ingested through contaminated food or milk, can increase a person's risk of developing thyroid cancer. The thyroid functions to absorb and store iodine, but it can hold only so much, and will just as readily absorb non-radioactive potassium iodide as radioactive iodine. Because of this, one dose of potassium iodide, which is not harmful to the thyroid, works by filling the gland so it cannot take up any radioactive iodine.