The chemical symbol for a drug called potassium iodide. KI-potassium iodide comes in the form of tablets. KI protects only the thyroid gland from just one kind of radiation — radioactive iodide. It can be obtained through your county and kept on hand in your home. KI is also available over the counter (without a prescription) at local pharmacies. In the event of a nuclear emergency, you could be instructed to swallow a KI-potassium iodide tablet. It should be taken only when directed by public officials