Most stomach upsets on a trip — cramping, diarrhea, a day of nausea — settle within a day or two, and the priority is fluids rather than medication. What matters is spotting the smaller number of cases that need a doctor: blood in your stool, a high fever, signs of dehydration, or symptoms that keep going for several days.
Japan makes the fluids part easy. Convenience stores and drugstores stock oral rehydration solution — OS-1 is the one you'll see most often — which replaces salts as well as water and is far more useful than sipping tea.
What to do in the first 24 hours
- Rehydrate steadily. Oral rehydration solution from a convenience store or drugstore, in small frequent sips rather than large glasses.
- Rest, and clear your plans. Trying to keep an itinerary while dehydrated is what turns a bad day into a lost trip.
- Eat lightly when you feel able — plain rice, congee, bread, bananas. Japanese convenience stores are unusually good for this.
- Wash your hands properly, and avoid preparing food for anyone you're traveling with until you're better.
- Keep a note of when it started, how often you're going, and whether there's fever or blood. A doctor will ask exactly this.
Be cautious with anti-diarrheal medication bought off a shelf. It can be the wrong choice for some infections, and it's one of the things worth asking a pharmacist or a doctor about rather than deciding yourself.
When to see a doctor
- Blood in your stool, or black, tarry stools.
- A high fever alongside the stomach symptoms.
- Signs of dehydration: very little urine, dizziness on standing, a dry mouth, unusual drowsiness.
- Vomiting that stops you keeping fluids down at all.
- Symptoms lasting more than about three days, or getting worse rather than easing.
- Severe or localized abdominal pain, particularly if it settles in one spot.
- You're pregnant, elderly, or have a condition that makes dehydration riskier.
Severe or localized pain deserves particular attention: some abdominal conditions need an examination and tests that no video call can provide, and delaying those is the real risk. A doctor who suspects one will tell you to be seen in person.
Food safety in Japan, briefly
Japan has high food-hygiene standards and tap water is safe to drink throughout the country, so the common causes here are less about contaminated water than about a new diet, unfamiliar ingredients, alcohol, exhaustion, and the occasional bad meal. Raw fish and raw egg are ordinary parts of Japanese cooking; if you're not used to them, introduce them gradually rather than on your first night.
What an online consultation can do
For mild to moderate symptoms, a video consultation with an English-speaking, Japan-licensed physician is a practical way to get assessed without leaving your room — which matters more than usual when you don't want to be far from a bathroom. The doctor reviews your symptoms and history and decides what's appropriate; if a prescription is warranted, it's emailed to you and sent to a pharmacy near you, often ready in as little as 30 minutes.
Consultations run 9:00–18:00 JST, Monday to Saturday, and booking is open at any hour. What a video call can't do is examine your abdomen or run stool and blood tests, so if the picture points that way you'll be referred for in-person care instead. If you're weighing up all your options rather than these symptoms specifically, start with our guide to getting sick in Japan.
When it probably isn't food poisoning
Not every upset stomach on a trip is something you ate. A sudden change in diet, far more walking than usual, dehydration in a Japanese summer, alcohol, jet lag and stress all disturb digestion by themselves. Nausea with a headache and poor sleep is often just exhaustion catching up.
The distinction matters less than the pattern, though. Whatever caused it, the questions are the same: are you keeping fluids down, is there fever or blood, is the pain localized, and is it getting better or worse? Those answers decide the next step, not your best guess at the meal responsible.
Traveling on while you recover
- Shinkansen and limited express trains have toilets; local trains and buses often don't. Plan long journeys around that, and use the station toilet before boarding.
- Public toilets in Japan are plentiful, clean, and free — in stations, department stores and convenience stores. This is one problem the country makes easier.
- Keep rehydrating on travel days, not just rest days. Long train journeys in summer are dehydrating.
- Tell your accommodation if you need to stay in. Most will help with laundry, extra water, or a later checkout.
- Don't prepare food for travel companions until you're properly better.
If symptoms are dragging on and you have onward travel booked, get assessed before you move rather than after. A doctor can advise on whether traveling is sensible, and if a flight or booking has to change, an English medical certificate is issued with every consultation for the airline or your insurer.
Where can I buy oral rehydration solution in Japan?
Convenience stores and drugstores stock it — OS-1 is the most widely available. It's more effective than water alone because it replaces salts as well as fluid.
Is tap water safe to drink in Japan?
Yes, tap water is safe to drink throughout Japan, so it's rarely the cause of stomach trouble here.
Should I take an anti-diarrheal medication?
Ask a pharmacist or a doctor first. It isn't the right choice for every cause of diarrhea, particularly where there's fever or blood.
How long is too long?
Symptoms lasting beyond about three days, or worsening at any point, are a reason to be assessed rather than to keep waiting — as are fever, blood, or any sign of dehydration.
