Potassium iodide and radiation

What is Potassium Iodide (KI)?
Potassium iodide (also called KI) is a salt of stable (not radioactive) iodine. Stable iodine is an important chemical needed by the body to make thyroid hormones. Most of the stable iodine in our bodies comes from the food we eat. KI is stable iodine in a medicine form.

What does KI do?
Following a radiological or nuclear event, radioactive iodine may be released into the air and then be breathed into the lungs. Radioactive iodine may also contaminate the local food supply and get into the body through food or through drink. When radioactive materials get into the body through breathing, eating, or drinking, we say that “internal contamination” has occurred. In the case of internal contamination with radioactive iodine, the thyroid gland quickly absorbs this chemical. Radioactive iodine absorbed by the thyroid can then injure the gland. Because non-radioactive KI acts to block radioactive iodine from being taken into the thyroid gland, it can help protect this gland from injury.

What KI cannot do
Knowing what KI cannot do is also important. KI cannot prevent radioactive iodine from entering the body. KI can protect only the thyroid from radioactive iodine, not other parts of the body. KI cannot reverse the health effects caused by radioactive iodine once damage to the thyroid has occurred. KI cannot protect the body from radioactive elements other than radioactive iodine—if radioactive iodine is not present, taking KI is not protective.

How does KI work?
The thyroid gland cannot tell the difference between stable and radioactive iodine and will absorb both. KI works by blocking radioactive iodine from entering the thyroid. When a person takes KI, the stable iodine in the medicine gets absorbed by the thyroid. Because KI contains so much stable iodine, the thyroid gland becomes “full” and cannot absorb any more iodine—either stable or radioactive—for the next 24 hours.
Iodized table salt also contains iodine; iodized table salt contains enough iodine to keep most people healthy under normal conditions. However, table salt does not contain enough iodine to block radioactive iodine from getting into your thyroid gland.

How well does KI work?
Knowing that KI may not give a person 100% protection against radioactive iodine is important. How well KI blocks radioactive iodine depends on
1. how much time passes between contamination with radioactive iodine and the taking of KI (the sooner a person takes KI, the better),
2. how fast KI is absorbed into the blood, and
3. the total amount of radioactive iodine to which a person is exposed.

Medical conditions that may make it harmful to take KI
Taking KI may be harmful for some people because of the high levels of iodine in this medicine. You should not take KI if
1. you know you are allergic to iodine (If you are unsure about this, consult your doctor. A seafood or shellfish allergy does not necessarily mean that you are allergic to iodine.) or
2. you have certain skin disorders (such as dermatitis herpetiformis or urticaria vasculitis).

People with thyroid disease (for example, multinodular goiter, Graves’ disease, or autoimmune thyroiditis) may be treated with KI. This should happen under careful supervision of a doctor, especially if dosing lasts for more than a few days.

You should only take potassium idodide (KI) on the advice of emergency management officials, public health officials or doctor.
 
Source: Centers for Disease Control and Prevention