Short answer. In Japan, local governments pre-distribute stable iodine (potassium iodide) to residents within about 5 km of nuclear facilities (PAZ). Within about 30 km (UPZ) it is handed out urgently at evacuation or relocation, or pre-distributed where the local government judges it necessary 1. Take it only when instructed, after the Nuclear Regulation Authority (NRA) judges it necessary 1.
Who receives stable iodine?
The NRA guide Distribution and administration of stable iodine (fully revised 3 July 2019, partially revised 23 December 2024) sets the rules 1:
| Zone | Radius | How tablets are provided |
|---|---|---|
| PAZ | about 5 km | Local governments must pre-distribute, in principle after a briefing by a doctor, or via designated pharmacies with a pharmacist's explanation |
| UPZ | about 30 km | Local governments must be able to distribute urgently at evacuation or relocation; pre-distribution where they judge it necessary, e.g. areas that may evacuate immediately like the PAZ, or where collecting tablets at distribution points would be difficult |
Stocks are also kept at public facilities, including for temporary visitors 1.
Pre-distribution targets in principle people under 40, plus pregnant and breastfeeding women and women wishing to conceive. People aged 40 and over may receive tablets on request 1. Pregnant women, breastfeeding women, infants and minors are the priority groups for taking it 1.
When should I take it?
Only on instruction. The NRA judges whether it is necessary, and the Nuclear Emergency Response Headquarters or the local government then tells residents to take it: 「原則として、原子力規制委員会が必要性を判断し、その判断に基づき原子力災害対策本部又は地方公共団体は服用の指示を出し、住民等はその指示に基づき服用する。」 1
It is most effective when taken from 24 hours before to 2 hours after exposure 1. Iodine disinfectants, gargles and iodine-rich foods are not substitutes 1.
What is the dose?
| Age | Single dose of potassium iodide (KI) |
|---|---|
| Under 1 month | 16.3 mg (jelly) |
| 1 month to 3 years | 32.5 mg |
| 3 to 13 years | 50 mg (1 pill) |
| 13 and over | 100 mg (2 × 50 mg pills) |
Source: NRA 1. Follow the instructions given with your tablets and by the authorities. Background on how iodine works and its limits: /guides/potassium-iodide.
Can I buy potassium iodide at a pharmacy in Japan?
This has not been confirmed. Potassium iodide 50 mg pills are registered as a medical-use drug (医療用医薬品) in the category "other than prescription drug" (処方せん医薬品以外の医薬品) 2. The national guide only describes distribution by local governments, and no official source we found states whether pharmacies may sell them to the public for nuclear preparedness 12. If you live near a nuclear facility, ask your municipality how tablets are distributed where you live.
What else protects me in a nuclear emergency?
Iodine protects only the thyroid against radioactive iodine. The Cabinet Secretariat pamphlet advises covering your mouth and nose with a handkerchief or similar and leaving the area immediately in a nuclear incident 3. Read /guides/shelter-or-evacuate, /guides/radiation-decontamination and /guides/nuclear-plant-zones.
Frequently asked questions
I live 20 km from a nuclear plant. Will I get tablets in advance?
Within the UPZ (about 30 km), tablets are handed out urgently at evacuation, unless your local government decides to pre-distribute 1.
I am over 40. Can I get iodine?
Yes, on request; pre-distribution targets people under 40 in principle 1.
Can iodine-rich food or an iodine gargle replace the tablets?
No. The NRA states these are not substitutes 1.
When is iodine most effective?
From 24 hours before to 2 hours after exposure, and only when the authorities instruct it 1.
Sources
- 原子力規制庁 (Nuclear Regulation Authority) — 安定ヨウ素剤の配布・服用に当たって（令和６年12月23日一部改正） — https://www.nra.go.jp/data/000480577.pdf (accessed 2026-10-20)
- 医薬品医療機器総合機構 (PMDA) — ヨウ化カリウム丸50mg「日医工」 医療用医薬品 詳細表示 — https://www.pmda.go.jp/PmdaSearch/iyakuDetail/530169_3221002L1074_1_09 (accessed 2026-10-20)
- 内閣官房 (Cabinet Secretariat) — 武力攻撃やテロなどの緊急事態から身を守るために（パンフレット） — https://www.kokuminhogo.go.jp/gaiyou/shiryou/hogo_manual.html (accessed 2026-10-20)
Turn this into action
Your plan for Japan, worked out for your household.
- Water, food and equipment counted for each person and pet
- The nuclear plants and zones around your home
- Phaenyx Safe: one tap to tell your people you are safe
Sources
- 原子力規制庁 (Nuclear Regulation Authority) · 安定ヨウ素剤の配布・服用に当たって（令和６年12月23日一部改正） checked 2026-10-20
- 医薬品医療機器総合機構 (PMDA) · ヨウ化カリウム丸50mg「日医工」 医療用医薬品 詳細表示 checked 2026-10-20
- 内閣官房 (Cabinet Secretariat) · 武力攻撃やテロなどの緊急事態から身を守るために（パンフレット） checked 2026-10-20