Mastigen in Japan: Iron Tablet Dose, Precautions and When to Seek Help

Tired or dizzy and wondering whether to buy iron in Japan? Symptoms alone do not establish iron deficiency. Mastigen tablets (マスチゲン錠) are an OTC anaemia medicine, not a general energy supplement.

I’m Irene, a pharmacist from Taiwan working in a Japanese drugstore. This guide helps you read the Japanese Mastigen label and prepare questions for a pharmacist. It is not a diagnosis, prescription or personal product review.

Checked: 22 October 2026, Japan time. Scope: Japan’s adult Mastigen tablets only, not other iron medicines, supplements or the children’s formulation.

Check warning signs before shopping for iron

If you suspect anaemia, arrange medical assessment and blood tests. Tiredness, pale skin or dizziness cannot establish the cause. Heavy periods, pregnancy or bleeding in the digestive tract may need investigation. Feeling somewhat better does not prove the underlying problem is resolved.

Identify the adult medicine, not just the brand

The approved Japanese indication is anaemia. Each adult tablet contains soluble ferric pyrophosphate 79.5 mg (equivalent to 10 mg iron), vitamin C 50 mg, vitamin E acetate 10 mg, vitamin B12 50 micrograms and folic acid 1 mg. These are medicine ingredients, not daily dietary targets or a conversion guide for other iron tablets.

The current adult range lists bottles of 30, 60 and 120 tablets. The separate “8–14歳用” formulation is marked as discontinued on the manufacturer’s dedicated site. Do not halve an adult tablet to make a child’s dose. “120 days” on a bottle describes the quantity at the labelled dose, not permission to self-treat for 120 days without review.

Do not combine versus ask before taking

• Do not combine: other medicines for anaemia while taking Mastigen.
• Consult a doctor, pharmacist or registered OTC medicine seller first: if receiving medical treatment, pregnant or possibly pregnant, or if you have previously had allergic symptoms from medicines or other substances. These are consultation requirements, not blanket bans.
• Age: this adult product’s dosing applies only to ages 15 and over. Do not use it for a younger child yourself.

Show the pharmacist all prescription and OTC medicines, iron supplements and multivitamins; mention breastfeeding too. The stated combination ban is not an assurance that every other combination is safe. Do not stop prescribed treatment to switch to this product yourself.

How to follow the Japanese dose

1. Ages 15+: one tablet once daily after food. Being more tired is not a reason to increase the dose.
2. Swallow with water or lukewarm water, without chewing. The tablet is designed to dissolve in the intestine.
3. Avoid gyokuro, sencha, coffee and black tea for 30 minutes before and 30 minutes after taking it. The label permits hojicha, bancha, oolong, genmaicha and barley tea; use water or lukewarm water to swallow the tablet.

If symptoms have not improved after about two weeks, stop taking it and bring the box when consulting a doctor, pharmacist or registered OTC medicine seller. Do not wait two weeks if symptoms worsen or warning signs appear. This is not a guaranteed cure time. If you improve but plan to continue, ask about the treatment duration and follow-up testing instead of using a larger bottle as a reason to postpone review.

Side effects and dark stools

Stop immediately and consult if you develop a rash, redness, itching, nausea, vomiting, loss of appetite, stomach discomfort or abdominal pain after taking it. Stop and consult if constipation or diarrhoea persists or worsens.

Iron can darken stools, but do not assume every black stool is a harmless medicine effect. Black or dark-red stools or bloody diarrhoea need urgent medical assessment; ongoing or heavy bleeding needs emergency help. Explain when the colour changed, whether you have started iron and any other symptoms.

What to bring to a Japanese pharmacy

1. When symptoms began, whether they are worsening, bleeding or period changes, and any previous blood-test results or anaemia diagnosis.
2. Your age, pregnancy or breastfeeding status, allergies, conditions, and all medicines and supplements.
3. A photo of the full product name, ingredients and directions. Confirm the adult Mastigen product and ask when to seek review or stop.

Keep the original box and directions. Close the bottle tightly and store somewhere cool, dry, away from direct sun and out of children’s reach. Do not transfer tablets, handle with wet hands or return touched tablets to the bottle. Do not swallow the desiccant or use expired medicine. Iron overdose can be very dangerous for children. Read the complete label on your pack; this guide cannot replace individual medical care.