For more information, see www.nuclearrisk.be
Anyhow, you should never take those tablets on your own initiative. You should wait until the government advises you to take them.
As a reminder: stable iodine tablets protect the thyroid gland in case of inhalation of radioactive iodine. One should know that the thyroid gland has a property to store iodine, whether or not it is radioactive. To avoid inhaled radioactive iodine to be stored in the thyroid gland, it is advisable to saturate it beforehand with non-radioactive iodine by taking stable iodine tablets. These contain only ordinary iodine (non-radioactive), that is stored in the thyroid gland, thus preventing that radioactive iodine be stored. This may be compared to a sponge that is soaked with pure water, and therefore cannot be polluted by soiled water.
Note however that the tablets only protect you from the consequences of radioactive iodine, and not from the effect of any other radioactive substances. It is therefore important to carefully follow the governments’ instructions.