What pill form is used for radiation?

Potassium Iodide (KI)

What You Need to Know
In a radiation emergency, some people may be told to take potassium iodide (KI) to protect their thyroid.
Do not take KI unless instructed by public health or emergency response officials or a health care provider.
There are limits to who should use KI and how much it can help. It only protects the thyroid from radioactive iodine (I-131) and does not protect other parts of the body from other types of radiation.
KI is recommended only for people under 40 and pregnant or breastfeeding people. Doses recommended by the U.S. FDA depend on age.
KI can have harmful health effects, especially if not needed or not taken correctly. If you are instructed to take KI, only use KI products that are approved by the U.S. FDA.

Potassium iodide (KI) is a type of iodine that is not radioactive and can be used to help block one type of radioactive material, radioactive iodine (I-131), from being absorbed by the thyroid.

In some radiation emergencies, usually nuclear power plant accidents, radioactive iodine may be released into the environment and enter the body through breathing or eating it. This is known as internal contamination. When the thyroid absorbs high levels of radioactive iodine, it can increase the risk of thyroid cancer in infants, children, and young adults many years after exposure. The thyroid is a gland in the neck that plays an important role in many body functions.

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Potassium Iodide (KI) and Radiation Emergencies | [Spanish]

How KI Protects the Thyroid
KI and radioactive iodine are both types of iodine. They are both absorbed by the thyroid. For KI to work, a person must take it before or shortly after exposure to radioactive iodine. When a person takes the right amount of KI at the right time, it can help block the thyroid from absorbing radioactive iodine. This happens because the thyroid has already absorbed the KI, and there is no room to absorb the radioactive iodine. Think of filling a jar with blue marbles. If you then pour green marbles over the jar, there will not be room and they will just spill out.

Use KI Only if Instructed
Do not take KI unless you are instructed by public health or emergency response officials or a health care provider. KI can cause harmful health effects. KI is helpful only in specific situations for certain groups of people.

KI should be used only as directed.

Do not use table salt or foods as a substitute for KI. They do not help with radiation poisoning and eating large amounts could be harmful.
Only use KI products that have been approved by the Food and Drug Administration (FDA). Dietary supplements that contain iodine may not work to protect the thyroid and can hurt you.

Source: Centers for Disease Control and Prevention
National Center for Environmental Health (NCEH), Emergency Management, Radiation and Chemical Branch
U.S. Department of Health and Human Services