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Potassium Iodide

December 2004

By Jon VanZile

LE Magazine December 2004
Potassium Iodide
Protecting Yourself In a Nuclear Emergency
By Jon VanZile

Chernobyl: Lessons Learned
Fortunately, scientists have not had much opportunity to study the effects of a nuclear emergency on human beings. Nuclear weapons have been used only twice against people, in Hiroshima and Nagasaki, Japan, near the end of the World War II. There have been only a handful of nuclear reactor meltdowns, and only one that released deadly levels of radioactive energy. It occurred in April 1986, at a nuclear reactor in Chernobyl, Ukraine.

Chernobyl was the first nuclear emergency large enough to threaten the health and well-being of millions of people. During that catastrophe, one of the main reactors of the power plant melted down, releasing an estimated 120 million curies of radioactive material. The surrounding land was heavily contaminated with plutonium and cesium, as well as with dangerous levels of radioactive iodine. Ultimately, more than 21,000 square kilometers of land were contaminated, and about 135,000 people were permanently evacuated. Experts later estimated that 17 million people were exposed to excess radiation,4 including 2.3 million children living in eastern Russia, southern Belarus, and northern Ukraine.5

At first, scientists did not appreciate the threat posed by high levels of radioiodine released during the meltdown. It did not take long, however, to start seeing the effects. Within four years, there was a sharp spike in the incidence of thyroid cancer.1 This increase occurred in children who had received less than 30 rems of radioiodine to the thyroid.6 Within 15 years, more than 1,000 cases of thyroid cancer had been reported in the affected areas, a 30- to 60-fold increase.6 All of the cases, according to the World Health Organization, were “most probably solely attributable to this single release of radioactivity to the environment.”5 Significantly, none of these areas made potassium iodide widely available.

Following the Chernobyl meltdown, Poland immediately distributed 17 million doses of potassium iodide, including 10 million to children. This was the first time scientists had an opportunity to study the side effects of potassium iodide in a large population. The news was encouraging: side effects were clinically insignificant.6

Awful as it was, the Chernobyl experience confirmed a valuable lesson: children are by far the most vulnerable to radiation exposure, even in relatively small doses.7 Children exposed to radiation suffer from higher rates of certain childhood cancers, especially leukemia and thyroid cancer, and have a greater likelihood of developing breast cancer as adults.7

Children’s greater vulnerability to radiation exposure is attributable to several factors, according to the American Academy of Pediatrics. First, children have higher minute ventilation, or a higher concentration of tiny capillaries in the lungs. This leads to greater radioactivity exposure from the same amount of radioactive material. Second, children are extra sensitive to the DNA-damaging effects of radioactive energy. Finally, children are more likely than adults to suffer from long-term psychological injury due to a radiation disaster.1

TABLE 1: Potassium Iodide Dosage Guidelines

Patient age

Exposure in grays*

Potassium iodide dosage

Over 40 years

Less than 5

130 mg

18 - 40 years

Less than .1

130 mg

12 - 18 years

Less than .05

65 mg

3 - 12 years

Less than .05

65 mg

1 month - 3 years

Less than .05

32 mg

Birth - 1 month

Less than .05

16 mg

Pregnant or lactating

Less than .05

130 mg

* A gray is the International System of Units (SI) unit of energy for the absorbed dose of radiation.
One gray is the absorption of one joule of radiation energy by one kilogram of matter.
One gray equals 100 rad, an older unit.

Guidelines for Protection
Fortunately, adults and children who are given potassium iodide may be completely protected from radioiodine. According to the Federal Register, “potassium iodide should be stockpiled and distributed to emergency workers and institutionalized persons for radiological emergencies at a nuclear power plant and its use should be considered for the general public within the 10-mile emergency planning zone of a nuclear power plant.”8

Significantly, however, this is only a recommendation. The final decision to stockpile potassium iodide has been left to state and local governments. Although the NRC has made free doses available to local governments, a significant number of cities and states have chosen not to participate in the program. As a result, you cannot be sure whether your local government has adequate supplies of potassium iodide. Fortunately, potassium iodide pills are available over the counter.

While the government recommends stockpiling within a 10-mile radius of a nuclear reactor, there is good reason to believe that people within a larger area should take precautions. The distribution of radioiodine is affected by wind patterns. In Chernobyl, the areas of greatest contamination were the 20-mile zone around the reactor, another region 120 miles north-northeast of the reactor, and yet another area 300 miles northeast of the reactor.1

In heavily congested areas—like southeastern New York state, which is close to five nuclear reactors—the American Academy of Pediatrics recommends stockpiling potassium iodide within a 50-mile radius. Other proposals have suggested a 200-mile radius.1

FDA-approved potassium iodide is available in 130-mg and 65-mg pills. The government has issued dosage guidelines for home use of potassium iodide, as shown in Table 1 above.

Potassium iodide can be dissolved in any liquid. Because it tastes salty, the FDA recommends dissolving it in pleasant-tasting solutions when administering it to children. Fruit beverages, including orange juice and raspberry drink, seem to hide the flavor. Chocolate milk and flat cola also can help mask the taste. Water and low-fat milk do not disguise the unpleasant taste. Each dose of potassium iodide lasts for 24 hours.


The use of potassium iodide to protect people from radiation exposure is supported by a wide array of governmental and medical organizations, including:

American Academy of Pediatrics:
“All children at risk should receive potassium iodide before exposure, if possible, or immediately afterward. This will require that potassium iodide be available in homes located within 10 miles of a nuclear power plant. Childcare facilities within 10 miles of a nuclear power plant should plan to stockpile the agent. It may be prudent to consider stockpiling potassium iodide within a larger radius because of more distant windborne fallout.”1

US Food and Drug Administration:
“The effectiveness of potassium iodide as a specific blocker of thyroid radioiodine uptake is well established, as are the doses necessary for blocking uptake. As such, it is reasonable to conclude that potassium iodide will likewise be effective in reducing the risk of thyroid cancer in individuals or populations at risk for inhalation or ingestion of radioiodines.”6

World Health Organization:
“The selective and rapid concentration and storage of radioactive iodine in the thyroid gland results in internal radiation exposure of the thyroid, which may lead to an increased risk of thyroid cancer and benign nodules and, at high doses, hypothyroidism. These risks can be reduced or even prevented by proper implementation of stable [potassium] iodine prophylaxis.”5

US Nuclear Regulatory Commission:
“Potassium iodide, if taken within the appropriate time and at the appropriate dosage, blocks the thyroid gland’s uptake of radioactive iodine and thus reduces the risk of thyroid cancers and other diseases that might otherwise be caused by thyroid uptake of radioactive iodine that could be dispersed in a severe reactor accident.”9

Limitations of Potassium Iodide
Although potassium iodide has shown powerful benefits in protecting people, and especially children, against a nuclear emergency, health officials stress that it is not a perfect solution. According to the NRC, the first line of defense during a nuclear emergency is evacuation. If evacuation is impossible, sheltering is the next best solution. Ideally, people should seek shelter in concrete buildings, even skyscrapers. If exposure does occur, any contaminated clothes should be removed and discarded as soon as possible.

Potassium iodide is not entirely without side effects. In newborns, potassium iodide has been shown to decrease the blood level of thyroxine and increase the level of thyroid stimulating hormone.1 In pregnant women, potassium iodide has been shown to cause neonatal hypothyroidism. In both cases, potassium iodide should be administered only as a last resort. People with iodine allergies should avoid potassium iodide.

Potassium iodide’s effectiveness also depends on the nature of the radioactive exposure. The drug is specifically geared to thyroid protection by blocking the uptake of radioiodine, a common beta particle produced during certain nuclear reactions. However, potassium iodide offers no protective benefits against other forms of radiation, including the extremely dangerous neutrons that are released during a nuclear explosion. It is also ineffective against so-called “dirty bombs,” which are constructed from radioactive material that does not contain radioiodine.

Finally, among older people and those in iodine-deficient areas, potassium iodide use has been associated with iodine-induced thyrotoxicosis. At chronic high doses, it has been shown to cause goiter or hypothyroidism. Because of this, people with multinodular goiter, Graves’ disease, and autoimmune thyroiditis should be use caution and consult a physician before using potassium iodide.6

Despite these limitations, potassium iodide, if used quickly and correctly, is the only pharmacological approach that has ever shown specific protective effects during a nuclear emergency.1


1. Radiation disasters and children. Pediatrics. 2003 June;111(6PT1):1455-66.

2. Takamura N, Hamada A, Yamaguchi N, et al. Urinary iodine kinetics after oral loading of potassium iodine. Endocr J. 2003 Oct;50(5):589-93.

3. Available at: Accessed September 15, 2004.

4. Weinberg AD, Kripalani S, McCarthy PL, Schull WF. Caring for survivors of the Chernobyl disaster. What the clinician should know. JAMA. 1995 Aug 2;274(5):408-12.

5. Available at: guide.pdf. Accessed September 19, 2004.

6. Available at: Accessed September 15, 2004.

7. Miller RW. Special susceptibility of the child to certain radiation-induced cancers. Environ Health Perspect. 1995 sep;103(Suppl 6):41-4.

8. Federal Emergency Management Agency. Federal Policy on the Use of Potassium Iodide (potassium iodide). Federal Register. 2002 Jan 10;:67(7):1355-6.

9. Available at: Accessed September 19, 2004.