Switzerland is distributing iodide tablets to more than half the country’s population for use in the event of a nuclear disaster.

Everyone living within a 50-kilometer radius of a nuclear power plant will in coming weeks be receiving packages of 12 pills that can keep for a decade. That’s 4.6 million people in a country of 8.1 million, according to the Federal Office of Public Health.

The tablets are being distributed between Oct. 27 and Dec. 5, Daniel Dauwalder, a spokesman for the Federal Office of Public Health, said by telephone from Bern today.

Following the 2011 Fukushima disaster in Japan, the Swiss federal government decided to broaden the pre-distribution radius from 20 kilometers for the pills, which can help prevent the accumulation of radioactive iodine in the thyroid. The policy of handing them out in urban centers such as Zurich and Basel within 12 hours of a disaster was no longer workable, the government decided.

The drug prevents thyroid cancer in people exposed to high levels of radiation by saturating the thyroid gland with so much normal iodine it can’t absorb any radioactive iodine.

Iodide pills cannot protect the body from other radioactive elements and could in fact cause harm, according to information on the website of the U.S. Centers for Disease Control and Prevention.

The 30 million-franc ($31 million) program will be paid for entirely by the nuclear plant operators, the government said.