Stomach Medicine in Japan: OTC Guide for Upset Stomach, Diarrhea, and Heartburn
A pharmacist's guide to Japanese OTC stomach medicines (Gaster 10, Stoppa, Biofermin S, Seirogan, Ohta's Isan), organized by symptom for travelers and residents.
Stomach Medicine in Japan: OTC Guide for Upset Stomach, Diarrhea, and Heartburn
Sashimi, street food, unfamiliar seasonings — traveling or living in Japan can be great for your palate, but not always for your stomach. Digestive troubles are one of the most common health complaints among foreign visitors.
This guide covers five OTC stomach medicines you can buy at any Japanese pharmacy, organized by symptom.
Quick Reference: Which Medicine for Which Symptom?
| Symptom | Main option | OTC class |
|---|---|---|
| Indigestion, overeating | Ohta's Isan | Class 2 |
| Excess acid, heartburn | Gaster 10 | Class 1 |
| Loose stools, diarrhea | Stoppa EX | Class 2 |
| Food/water-related stomach upset | Seirogan | Class 2 |
| Bloating, gut-balance | Biofermin S | Quasi-drug (iyakubugaihin) |
Class 1 medicines require information provision by a licensed pharmacist (yakuzaishi) at the time of sale. Class 2 medicines can be sold by either a pharmacist or a registered seller (toroku-hanbaisha), though availability depends on the store's staffing. Quasi-drugs (iyakubugaihin) are a separate category from medicines; some may also be found at supermarkets or convenience stores, but availability varies by store.
1. Ohta's Isan — For Indigestion and Overeating
A long-selling Japanese stomach medicine. The classic version (Ohta's Isan) is a powder with a distinctive herbal/spice aroma.
- Combines antacid ingredients with digestive herbs
- Used for overeating, over-drinking, and indigestion
- Taken after or between meals
- Age-based dosing (check the package insert)
A separate tablet product (Ohta's Isan A Tablets) is also sold by the same maker. It has different dosing from the powder — for example, 3 tablets per dose for ages 15+, 2 tablets for ages 8–14, and 1 tablet for ages 5–7, taken after or between meals. Check the package of whichever product you buy.
2. Gaster 10 — For Heartburn and Excess Stomach Acid
Active ingredient: famotidine. It's an H2 blocker — the same molecule sold internationally as Pepcid.
- Used for heartburn, stomach pain, nausea, and excess acid
- 1 tablet, up to twice a day
- For ages 15 and up (not suitable for ages 80+)
- Class 1 — sold only at stores set up to handle Class 1 medicines
Because it's Class 1, the pharmacist will provide information and ask a few quick questions at the time of sale. Consult a doctor if symptoms don't improve after 3 days of use. Also seek care promptly — rather than continuing self-treatment — if you have vomiting blood, black/tarry stools, unintended weight loss, or difficulty swallowing, as these may signal conditions other than simple excess acid.
3. Stoppa Geridome EX — For Diarrhea
Active ingredient: loperamide hydrochloride. It slows gut motility to relieve diarrhea — the same drug sold internationally as Imodium.
- Used for loose stools and diarrhea
- Chewable tablet (can be taken without water)
- For ages 15 and up
- Up to 3 doses per day
Important: Diarrhea with fever, bloody stools, or severe abdominal pain may indicate infectious gastroenteritis (bacterial or viral). Suppressing gut motility with loperamide can worsen the illness in these cases. If you have any of these symptoms, do not self-treat — see a doctor.
4. Seirogan — For Food or Water-Related Stomach Upset
A long-selling Japanese stomach medicine. Small black pills with a strong, distinctive smell.
- Used for food/water-related upset, loose stools, diarrhea, and indigestion
- Active ingredient: wood creosote (listed as "Japanese Pharmacopoeia Creosote" on the package insert)
- For ages 15+: 3 pills per dose, 3 times a day
- For ages 5 and up (age-based dosing)
A sugar-coated version (Seirogan Tōi A / 正露丸糖衣A) is also available, with a much milder smell.
Important: If diarrhea is accompanied by fever, bloody stools, or severe abdominal pain, infectious gastroenteritis may be the cause. Do not self-treat with Seirogan in these cases — see a doctor.
5. Biofermin S — For Bloating and Gut Balance
A probiotic (lactic acid bacteria preparation) that supports beneficial gut flora. Widely used as a gut-regulating product in Japanese households.
- Used for loose stools, constipation, and bloating
- Adults: 3 tablets, 3 times a day (after meals)
- For ages 5 and up (age-based dosing)
- Generally considered gentle and suitable for longer-term use
Note on the Biofermin brand: The brand covers several products and their classifications differ by item. "Biofermin S Tablets" and "New Biofermin S Tablets" are separate products (different bacterial strain combinations), and there is also "Biofermin Shisha-yaku," an anti-diarrheal classified as Class 2. Classification and legal category can vary by product, so always check the label of the specific item you're buying rather than assuming all Biofermin products behave the same way.
How to Buy at a Japanese Drugstore
Useful Japanese phrases
- Onaka wo kowashimashita. — "I have an upset stomach."
- I ga motarete imasu. — "My stomach feels heavy."
- Geri-dome ga hoshii desu. — "I'd like anti-diarrheal medicine."
- Muneyake ni kiku kusuri wa arimasu ka? — "Do you have something for heartburn?"
What to tell the staff
- How many days the symptoms have lasted
- Whether you have fever, bloody stool, or vomiting
- Any other medicines you're taking
- Pregnancy or breastfeeding status
When to See a Doctor Instead
Skip self-treatment and seek medical care if you have any of the following:
- Diarrhea with fever above 38°C (100.4°F)
- Bloody or black stools
- Severe vomiting lasting more than 24 hours
- Intense abdominal pain
- Signs of dehydration (dry mouth, no urine, dizziness) — especially combined with high fever
With Japan's national health insurance, you pay only 30% of the cost to visit an internal medicine (naika) or gastroenterology (shōkaki-naika) clinic. For urgent symptoms at night or on holidays, call #7119 (the emergency consultation line) to ask whether you should seek care.
Warning: Similar Names and Lookalike Packaging
Japanese stomach medicines come in many variants. Always check both the product name and the active ingredient on the package.
- Gaster 10 tablets vs. Gaster 10 S Powder (same ingredient, different form)
- Seirogan vs. Seirogan Tōi A / 正露丸糖衣A (same ingredient, sugar-coated version with reduced smell)
- Biofermin S vs. New Biofermin S (separate products by the same maker, different bacterial strain combinations — always check the specific package)
Frequently Asked Questions
Q. Can I bring Imodium from home for use in Japan? A. Personal-use quantities (generally up to one month's supply) are allowed. You can also buy loperamide products (Stoppa EX) at Japanese pharmacies.
Q. Seirogan smells too strong — is there an alternative? A. Yes — Seirogan Tōi A (正露丸糖衣A) is sugar-coated and has a much milder smell.
Q. Can I take Biofermin S every day? A. It's generally considered gentle and suitable for longer-term use, and many Japanese households take it regularly. Stop and consult a pharmacist or doctor if symptoms worsen during use. Note that "Biofermin S" and "New Biofermin S" are separate products — check the package of the one you're buying.
Sources
- Gaster 10 package insert (Daiichi Sankyo Healthcare)
- Stoppa Geridome EX package insert (Lion Corporation)
- Seirogan package insert (Taiko Pharmaceutical)
- Biofermin S product information (Biofermin Pharmaceutical)
- Ohta's Isan product information (Ohta's Isan)
- Pharmaceuticals and Medical Devices Agency (PMDA)
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a licensed pharmacist or physician before taking any medication.