Many Californians were, and still are, concerned about the potential for radiation exposure following the Japanese earthquake and tsunami that damaged a nuclear reactor. This mainly concerns possible fallout of radioactive particles that might carry across the Pacific Ocean and settle on the West Coast. This has led to “panic” buying of potassium iodide pills and solutions from pharmacies for protection from radioactive iodine. In reality, taking these supplements may do more harm than benefit. When a nuclear accident or explosion occurs, harmful rays such as gamma rays can be released, but only travel a certain distance from the reactor. However, particles can be generated and released into the air, some of which are radioactive.  These particles can be inhaled or get into our water or food. They can then be taken into our bodies, where they can react with our organs. Some of these radioactive particles include radioactive iodine that gets into our thyroid gland. Some people who have radioactive iodine deposited into their thyroid gland can develop cancer or other thyroid problems days or years after the exposure.  By giving susceptible people potassium iodide (KI) supplements, one can “saturate” their thyroid gland with iodine, preventing uptake of radioactive iodine particles. The most susceptible individuals are children, pregnant women and people aged 18 to 40. Scientists believe detectable levels of radioactive particles in the United States, and in particular Southern California, should remain well within safe limits. If a large explosion occurs creating a significant fallout cloud, it would likely take several days to reach the United States. Studies show that KI needs to be taken within two hours after an exposure, so there is no need to buy or take iodine supplements at this time, and supplies should be released by government agencies to protect at-risk individuals if the need occurs. The standard treatment for radioactive iodine exposure is different depending on the age of the person, but for adults over 18, it is 130 mg of KI a day until the contamination is gone. There are potential side effects of KI, including possible life-threatening allergic reactions and damage to the thyroid gland. Anyone with allergies to iodine, seafood, or iodine-containing medications should not take iodine supplements. Individuals with a known or suspected thyroid condition should check with a health care provider before taking iodine supplements. It is important to remember that KI only protects the thyroid gland and the possible cancer-causing effects of the radioactive iodine. It won’t protect a person from any other source of radiation or nuclear fallout. Avoidance is the only other way to protect oneself from radiation related effects and cancers. This includes avoiding radioactive fallout if present, but it also consists of avoiding exposure to direct radiation such as x-rays. — Clark is medical director of the Poison Control Center in San Diego and the director of the UC San Diego Health System’s medical toxicology division.