Potassium iodide is a chemical compound, medication, and dietary supplement. As a medication it is used to treat hyperthyroidism, in radiation emergencies, and to protect the thyroid gland when certain types of radiopharmaceuticals are used. Potassium iodide crystals are a chemical compound commonly used in medicine and industry. It is primarily used to treat and prevent radiation exposure by protecting the thyroid gland from radioactive iodine. Additionally, it is used in the production of photographic film, as a nutritional supplement, and in the manufacturing of certain chemicals. Potassium iodide crystals are also used in the laboratory for analytical purposes.