Potassium iodide (KI) is a chemical compound that can be used to protect the thyroid gland from possible radiation injury caused by radioactive iodine (radioiodine) . In a radiological emergency, some people may be told to take KI to protect their thyroid gland from the effects of radiation from inhaled or swallowed radioactive iodine. KI works by filling the thyroid with a kind of iodine that prevents the thyroid gland from taking in any of the radioactive kind of iodine. When taken at the right time and in the right amount, KI can help block any inhaled or ingested radioactive iodine from being absorbed by the thyroid, which lowers the risk of radiation damage to that gland.

KI is only indicated in emergencies where the public is likely to be exposed to radioiodine. The use of KI is generally not recommended unless instructed by public health or emergency officials. KI can have harmful health effects, especially if not needed or not taken correctly. Harmful health effects may include gastrointestinal issues, skin rash, and thyroid problems in infants.

KI can be taken as an oral solution, syrup, uncoated tablet, or enteric-coated delayed-release tablet. Some brands of the oral solution are available without a prescription. Only KI products that are FDA-approved may be legally marketed in the United States. As of March 2022, these KI products are FDA-approved and are available without a prescription: iOSAT tablets, 130mg, from Anbex, Inc.; iOSAT tablets, 65mg, from Anbex, Inc.; ThyroSafe tablets, 65mg, from BTG INTERNATIONAL, Inc.; and Potassium Iodide Oral Solution USP, 65mg/mL, from Mission Pharmacal Company.

In general, most people can take KI without any problems, but its always important to talk to a doctor before using it. If you have certain medical conditions, it might not be a good idea to take the medication. Carefully watch babies to ensure their safety if they take KI.