日本大地震及海啸引发核泄露事故后，与受灾地区相邻的国家和地区近日出现了抢购碘化钾（即“碘片”）的热潮。

Japan's nuclear crisis is spiking¹ demand in the U.S. and a few other places for a cheap drug that can protect against one type of radiation damage — even though the risk is only in Japan.

Health agencies in California and western Canada warned Tuesday that there's no reason for people an ocean away to suddenly stock up（置办） on potassium（钾） iodide（碘化物） . Some key suppliers say they're back-ordered and are getting panicked calls from potential customers.

"Tell them, `Stop, don't do it,'" said Kathryn Higley, director of radiation health physics at Oregon State University.

"There's a lot of mythology²（神话） about the use of potassium iodide," added Dr. Irwin Redlener, a pediatrician and disaster preparedness specialist at Columbia University. "It's not a radiation antidote³ in general."

The pill can help prevent radioactive iodine⁴ from causing thyroid（甲状腺） cancer, for which children are most at risk in a nuclear disaster.

Japan's Nuclear Safety Agency has stored potassium iodide to distribute in case of high radiation exposure, and the U.S. Navy is giving it to military crews exposed to radiation as they help with relief efforts in Japan. But government and independent experts say that Americans have little to fear from any radiation released by the damaged Japanese nuclear plant.

"You just aren't going to have any radiological material that, by the time it traveled those large distances, could present any risk to the American public," said Nuclear Regulatory Commission Chairman Greg Jazcko.

Other governments echoed that warning.

"We do not expect any health risk following the nuclear reactor⁵ releases in Japan, nor is the consumption of potassium iodide tablets a necessary precaution," British Columbia's health ministry⁶ told the public Tuesday.

In Russia, where memory of the very different Chernobyl disaster 25 years ago is strong, media reports said pharmacies⁷ in Vladivostok, a major port just west of Japan, had run out of the pills.

What does this drug do?

Potassium iodide, a salt also known as KI, has just one use: It shields（保护，遮蔽） the thyroid from radioactive iodine. It blocks no other type of radiation, and protects no other body part.

The drug, either pill or liquid form, is sold over-the-counter and is considered safe, although some people may experience allergic⁸ reactions.

Potassium iodide is most important for children and pregnant women, because a growing thyroid is much more active and more likely to absorb radioactive iodine, said Columbia's Redlener. It should be given within a few hours of radiation exposure — but isn't considered that useful for people over age 40.