Today BBC report that Potassium iodide tablets were distributed among some US crops to prevent counter effects of potential radioactivity Japan's reactors. And it is heard that people all over the world searching for this tablet for help counter effects of potential radioactivity Japan's reactors.
I search about this tablets and found that in 1982 US FDA has approved this tablet for protect thyroid glands from radioactive iodine involving accidents or fission emergencies.
For more details please visit Wikipedia page
I heard that people try to use iodized salt to get Potassium iodide to fight against potential threats but unfortunately it is only a myth as you need to take approximately 80 spoons to equal sufficient amount.