Japan is a paradise for food lovers, but the combination of unfamiliar cuisine, irregular meal schedules, travel stress, and different water can disrupt the digestive system in various ways. Whether you're dealing with post-ramen stomach pain, traveler's constipation, food-related nausea, or an upset stomach from trying too many izakaya dishes in one evening, Japan's pharmacy shelves have a solution.
The challenge, as always, is the language barrier. This guide cuts through it with specific product names in both English and Japanese, clear explanations of active ingredients, and practical advice on where to find everything.
Types of Stomach Medicine
Japan's OTC gastric medicine falls into four main categories based on the problem being treated.
Antacids & Gastric Relief
Gastric discomfort — from indigestion, excess stomach acid, bloating, and general stomach pain — is treated with products categorized as *iyaku* (胃薬, stomach medicine).
Key gastric medicine products:
Ohta Isan (太田胃散) — Japan's most iconic stomach medicine, recognizable by its distinctive yellow tin. A complex herbal-mineral blend containing:
- Carmine (digestive stimulant)
- Gentian extract (bitter tonic)
- Sodium bicarbonate (antacid)
- Magnesium carbonate (antacid)
- Cinnamon and clove extracts (aromatic digestives)
Ohta Isan has been sold in Japan since 1879 and is a cultural institution. It is available as a powder (granule) or in tablet form. The powder is the original and most popular form — you dissolve it in water or take it directly. Excellent for post-meal indigestion, acid reflux, and general stomach discomfort.
Gascon (ガスコン) — contains simethicone (dimethicone) for gas and bloating relief. Simethicone breaks down gas bubbles in the stomach and intestines, reducing bloating and flatulence. Very gentle; can be used during pregnancy (consult a doctor first). Gascon tablets are chewable.
Maalox / Antepsin (antacid products) — magnesium/aluminum hydroxide antacids for acid reflux and heartburn. Similar to Tums or Rolaids. Available at most drugstores.
Gaviscon Japan — sodium alginate-based; creates a foam "raft" that floats on stomach acid to prevent reflux. Good for heartburn occurring while lying down.
Proton pump inhibitors (PPIs): In Japan, Nexium 10mg (ネキシウム) has been available OTC since 2015 — a historic change as PPIs were previously prescription-only. It is a Class 1 drug, requiring pharmacist dispensing. Very effective for chronic heartburn, acid reflux, or suspected gastritis. Note: not recommended for continuous use beyond 2 weeks without medical supervision.
For stomach cramps and pain: Antispasmodic products containing butylscopolamine (ブチルスコポラミン) or papaverine derivatives provide relief from cramping-type pain. Ask the pharmacist for *itai toki no kusuri* (胃が痛いときの薬).
Anti-Diarrheal
Diarrhea (*geri*, 下痢) is one of the most common travel health complaints globally. In Japan, it is often triggered by unfamiliar food, bacteria from raw seafood, or changes in diet and water.
Key anti-diarrheal products:
Seirogan (正露丸) — Japan's most famous anti-diarrheal medicine, instantly recognizable by its strong smell (it contains wood creosote, *mokusō kreosoto*). This distinctive odor is intentional — creosote has antiseptic properties that help with diarrhea caused by minor gastrointestinal infections. Seirogan has been sold since the early 1900s and is a fixture in Japanese medicine cabinets.
The smell can be off-putting to those unfamiliar with it, but the product is highly effective. Available in granule form (with sugar coating) and uncoated pills.
Loperamide (ロペラミド) — the same active ingredient as Imodium, available in Japan under various brand names including Stoppa (ストッパ) and Loperamide S (ロペラミドS). Fast-acting and highly effective for non-infectious diarrhea. Note: do not use if you have a fever or blood in the stool, as these suggest bacterial infection that should be treated differently.
Bifermin (ビオフェルミン) — probiotic tablets containing *Lactobacillus acidophilus*. Suitable for mild diarrhea, loose stool, and gut restoration after antibiotic use. Safe for children and pregnancy. Gentle but slower to work than loperamide.
For more detailed guidance on food poisoning specifically — including when symptoms indicate a serious bacterial infection — see our guide on food poisoning in Japan.
Constipation Relief
Traveler's constipation is extremely common, caused by disrupted routine, different diet, dehydration, and reduced physical activity. Japan's OTC constipation medicine is excellent.
Types of constipation medicine in Japan:
Stimulant laxatives (刺激性下剤) — the most common and fast-acting type. They stimulate the intestinal muscles to move stool along.
- Dulcolex (ダルコラックス) — bisacodyl tablets; standard stimulant laxative similar to products used worldwide. Tablets act in 6–12 hours; suppository form acts in 15–60 minutes.
- Senna-containing products (センナ) — herbal stimulant laxatives; very common in Japan. Many products are sold as *benpi no kusuri* (便秘の薬). Expect action in 6–12 hours.
- Picolax (ピコラックス) — sodium picosulfate; gentler stimulant, suitable for mild constipation.
Osmotic laxatives (浸透圧性下剤):
- Magnesium hydroxide products — draw water into the colon to soften stool. Gentle and appropriate for prolonged use. Available OTC in Japan as *oxidized magnesium* tablets.
Fiber supplements:
- Psyllium husk (*psyllium*, オオバコ) products are available at health food sections of pharmacies. Work slowly over days; best for prevention rather than acute relief.
Softeners / gentle options:
- Kasurē (カスルー) and similar herbal products — traditional herbal blends for constipation. Gentler than stimulant laxatives.
How to ask: Show the pharmacist *benpi no kusuri wo kudasai* (便秘の薬をください — "Please give me constipation medicine").
For most travelers, constipation resolves within a few days as the body adjusts to the new environment. If it persists beyond 5–7 days or is accompanied by significant pain, see a doctor.
Anti-Nausea
Nausea (*hakike*, 吐き気) during travel can have many causes: motion sickness, food-related illness, alcohol, medication side effects, or systemic illness.
Key anti-nausea products in Japan:
Motion sickness / travel sickness:
- Travamine (トラベルミン) — Japan's most recognized motion sickness medicine, containing diphenhydramine (antihistamine) + caffeine. Available in regular and children's formulations. Take 30 minutes before travel.
- Kwells (クウェルズ) — scopolamine-based; very effective for motion sickness, particularly sea and air travel.
Nausea from illness / food:
- Metoclopramide products — available OTC in some formulations for nausea associated with gastric disorders. Prescription-strength versions require a clinic visit.
- Domperidone (ドンペリドン) — prokinetic that helps gastric emptying; available OTC under certain brand names for functional nausea.
- Herbal preparations — several Japanese herbal (*kanpō*, 漢方) products are effective for nausea, including Hangekobokuto (半夏厚朴湯) and Rikkkunshito (六君子湯). Ask the pharmacist if you prefer a gentler, non-pharmaceutical approach.
For hangover nausea: Rehydration is the primary treatment. Japan has excellent oral rehydration drinks (*keiko suibun hokyū*, 経口水分補給) at convenience stores — look for OS-1 (オーエスワン), the medical-grade rehydration drink used in Japanese hospitals. Better than standard sports drinks for genuine dehydration and nausea from alcohol or illness.
Where to Buy (Including 7-Eleven)
Japan's convenience stores carry a surprisingly useful range of gastrointestinal medicine, particularly useful for late-night emergencies.
Product Category | Major Drugstore | Convenience Store (7-Eleven, etc.) | Supermarket |
|---|---|---|---|
Antacids (Ohta Isan, Maalox) | Full range | Basic products (1–2 options) | Some |
Gas / bloating (Gascon) | Yes | Sometimes | Sometimes |
Anti-diarrheal (Seirogan, Stoppa/loperamide) | Yes | Yes (Seirogan often stocked) | Some |
Probiotic (Bifermin) |
7-Eleven Japan is noteworthy for its pharmacy-adjacent product range. Most stores stock: Seirogan, Travamine, Ohta Isan granules, basic antacids, and OS-1. This makes it viable for middle-of-the-night stomach emergencies when drugstores are closed.
Major drugstore chains (Matsumoto Kiyoshi, Sundrug, Tsuruha, Welcia) carry the full range of every category listed above. For complex situations — persistent symptoms, pediatric cases, pregnancy, drug interactions — the pharmacist at these chains can provide excellent guidance.
For the full picture on how Japan's pharmacy system works — including the difference between Class 1, Class 2, and quasi-pharmaceutical products — see the Japan Pharmacy Guide.