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Background: Intake of potassium iodide (KI) reduces the accumulation of radioactive iodine in the thyroid gland in the event of possible contamination by radioactive iodine released from a nuclear facility. The World Health Organization (WHO) has stated the need for research for optimal timing, appropriate dosing regimen, and safety for repetitive iodine thyroid blocking (ITB). The French PRIODAC project, addressed all these issues, involving prolonged or repeated releases of radioactive iodine. Preclinical studies established an effective dose through pharmacokinetic modeling, demonstrating the safety of repetitive KI treatment without toxicity. Summary: Recent preclinical studies have determined an optimal effective dose for repetitive administration, associated with pharmacokinetic modeling. The results show the safety and absence of toxicity of repetitive treatment with KI. Good laboratory practice level preclinical studies corresponding to individuals >12 years have shown a safety margin established between animal doses without toxic effect. After approval from the French health authorities, the market authorization of the two tablets of KI, 65 mg/day, was defined with a new dosing scheme of a daily repetitive intake of the treatment up to 7 days unless otherwise instructed by the competent authorities for all categories of population except pregnant women and children under the age of 12 years. Conclusion: This new marketed authorization resulting from scientific-based evidence obtained as part of the PRIODAC project may serve as an example to further harmonize the application of KI for repetitive ITB in situations of prolonged radioactive release at the European and international levels, under the umbrella of the WHO.