Non-radioactive iodine, given as a dietary supplement, is one of the more effective anti-radiation treatments available.
The human body absorbs iodine when it can, and sends it straight to the thyroid gland for processing.
If that iodine happens to be radioactive, then there's a seed for potential cancers later.
Simply taking extra iodine first prevents the radioactive iodine from being absorbed. The body just says, "No thanks, I'm full."
Such preventive doses, I believe, were administered to local residents after the Three-Mile Island minor radiation release.
Thanks, Bob!