Most stomach upsets in Thailand pass on their own within a few days. The main job is to replace the fluid you lose, ideally with oral rehydration salts from a pharmacy, and to see a doctor quickly if warning signs appear, such as blood in the stool, a high fever, signs of dehydration or vomiting that stops you keeping fluids down.
This page is about what to do once you are already ill. It is general information, not medical advice: a pharmacist or doctor who sees you decides what you need. Our article on avoiding getting sick from street food covers prevention, and the guide to medicines you can buy over the counter explains how Thai pharmacies sort their stock. Facts below were checked in October 2026.
Stomach upset in Thailand: the essentials
- How common
- 30-70 % of travelers on a two-week trip, depending on destination and season (CDC, 2026)
- Usual length
- Bacterial 3-7 days, viral 2-3 days, untreated (CDC)
- First treatment
- Fluids; oral rehydration solution (ORS) for heavier fluid loss (CDC, WHO)
- Antibiotics
- Only on a doctor's or pharmacist's advice
- Ambulance
- 1669
The first 24 hours: fluids, rest and watching for change
Travelers' diarrhea is, in the words of the US Centers for Disease Control and Prevention (CDC), "the most predictable travel-related illness". Its 2026 Yellow Book puts the attack rate at 30 to 70 percent of travelers over a two-week trip. So if it happens to you, you are in large company, and careful eating does not make you immune: the CDC notes that even the old rule "boil it, cook it, peel it, or forget it" does not reliably prevent it.
Bacteria are the most common cause. Illness caused by a toxin in the food usually starts within a few hours of eating. According to the CDC, untreated bacterial diarrhea usually lasts three to seven days and viral diarrhea two to three days, while illness caused by parasites can go on for weeks.
For the first day, the UK's NHS advice is simple: rest, drink plenty, take small sips if you feel sick, and eat when you feel able to, avoiding fatty or spicy food for a while. The NHS also says not to drink fruit juice or fizzy drinks, because they can make diarrhea worse. Stay close to a toilet, and in Thailand's heat drink more than you think you need; our guide to coping with heat and sun explains why the climate adds to fluid loss.
Oral rehydration salts: the most useful thing a pharmacy sells
Oral rehydration solution, usually called ORS, is made from a packet of oral rehydration salts mixed with clean water. The World Health Organization (WHO) describes it as a solution of clean water, sugar and salt that replaces the water and electrolytes lost in diarrhea. The CDC says one packet is generally mixed with one liter of boiled or treated water, and that ORS is widely available at stores and pharmacies in most low- and middle-income countries.
In Thailand, ask at any pharmacy for oral rehydration salts. Follow the instructions on the packet exactly and use bottled or boiled water; our article on Thai tap water explains why. Sports drinks and sweet sodas are not the same thing.
Buy two packets of ORS on your first day in Thailand. They are light, cheap and easy to find in daylight in a city. They are much harder to find at 3 a.m. in a beach bungalow, which is when you will want them.
If you need a pharmacy after dark, our guide to late-night and 24-hour pharmacies lists where to look.
What else the pharmacy may offer, and what to be careful with
Thai pharmacists are used to travelers with stomach trouble and often speak some English in tourist areas. Describe your symptoms honestly: how long, how often, whether there is blood or fever, what you ate, and any medicines you already take or conditions you have. Let the pharmacist choose; this page gives no doses.
Medicines that slow the gut (the loperamide type) can make a long bus ride possible. But the CDC says they are not recommended on their own for people with bloody diarrhea or with diarrhea and fever, and they are rarely given to children under six. The NHS says not to give them to children under 12. If you have a fever or see blood, skip them and see a doctor.
The UK Foreign Office warns that medicine sold on the street may not be genuine. Buy from a proper pharmacy, check the packet is sealed and in date, and keep the box to show a doctor later.
Antibiotics: when doctors use them, and why not to guess
Many travelers have heard that Thai pharmacies sell antibiotics freely. Whether a particular antibiotic may be sold without a prescription is a question of Thai law that we could not confirm on an official source, so the only safe advice is: take antibiotics only when a doctor or pharmacist who has assessed you advises it.
The CDC gives good reasons to be careful. Antibiotics shorten bacterial diarrhea by only about one to two days, they raise the risk of picking up resistant bacteria, and taking them in advance to prevent illness is not recommended for most travelers. Resistance also matters in this region in particular: the CDC says resistance to the ciprofloxacin family of antibiotics, especially in Campylobacter bacteria, is common in South and Southeast Asia. That is why doctors here usually choose a different antibiotic when one is needed, and why a course a friend recommends from home may not work.
Old advice to take ciprofloxacin for a Thai stomach bug is out of date. The CDC says resistance to this antibiotic group is widespread in Southeast Asia. Let a doctor decide whether you need an antibiotic and which one.
Warning signs: when to see a doctor
The NHS lists signs that need medical help rather than home care. In Thailand, that means a clinic or hospital the same day, or an ambulance on 1669 for the most serious ones. See a doctor if you or your child:
- have bloody diarrhea or bleeding from the bottom;
- keep vomiting and cannot keep fluids down;
- still show signs of dehydration, such as dark urine or peeing much less than usual, after taking rehydration salts;
- have diarrhea for more than seven days or vomiting for more than two days;
- have a high fever, or a baby or young child is ill (see the next section).
The NHS treats these as emergencies: vomiting blood or vomit that looks like coffee grounds, green vomit, a stiff neck with pain when looking at bright lights, a sudden severe headache or stomach pain, blue, gray or blotchy skin or lips, severe difficulty breathing, or confusion. Call 1669 or go straight to a hospital emergency department. Our list of emergency numbers explains what to say on the phone.
Babies, children, older travelers and people with health conditions
The CDC says infants and young children are at greater risk of dehydration, and that ORS is the main treatment for children. The WHO adds that zinc shortens diarrhea episodes in children, but that is something for a doctor or pharmacist to decide on. Do not give children medicine to stop diarrhea unless a doctor tells you to.
The NHS also says older people, those with a weakened immune system, and people with conditions that raise the risk of dehydration should get advice early rather than wait. If you have diabetes, kidney disease or a heart condition, or you take medicines such as diuretics, ask a doctor how a stomach bug affects them. If you are pregnant, see a doctor rather than relying on a pharmacy.
At the clinic or hospital: what to expect and how payment works
For an ordinary case, a small private clinic or a hospital outpatient department can see you the same day. A doctor may examine you, ask for a stool test, and in some cases put you on a drip if you are badly dehydrated. Bring the medicines you have taken, including their boxes, and a short note of when the symptoms started.
The UK Foreign Office says all Thai hospitals require a guarantee of payment before treatment. How that works, the difference between private and government hospitals, and what to ask for at discharge are covered in our guide to hospitals in Thailand; this page does not repeat it.
Insurance and keeping the paperwork
If you are insured, call your insurer's assistance line before you agree to an admission, and keep every receipt, the doctor's certificate and the list of medicines. A short clinic visit may cost less than your policy excess; a hospital stay usually will not. Our page on travel insurance for Thailand explains what a policy should cover.
Eating again, and avoiding a second round
When the diarrhea settles, go back to plain food in small amounts: rice, rice soup (khao tom or jok), toast, bananas. Keep drinking. Most people feel normal again within a few days, but if symptoms keep coming back for weeks, see a doctor, because the CDC notes that parasites can cause illness lasting weeks to months. Raw freshwater fish dishes carry a separate risk; see our page on liver flukes and raw fish.
Frequently asked questions
How long does food poisoning last in Thailand?
Most cases pass within a few days. The CDC says untreated bacterial diarrhea usually lasts three to seven days and viral diarrhea two to three days. The NHS says to get medical help if diarrhea lasts more than seven days or vomiting more than two days.
Where can I buy oral rehydration salts in Thailand?
Ask at any pharmacy for oral rehydration salts (ORS). The CDC notes that ORS is widely available at stores and pharmacies in most low- and middle-income countries. Mix it exactly as the packet says, with bottled or boiled water.
Should I take antibiotics for travelers' diarrhea in Thailand?
Only if a doctor or pharmacist who has assessed you advises it. The CDC says antibiotics shorten bacterial diarrhea by only one to two days and raise the risk of resistant bacteria, and that resistance to the ciprofloxacin group is common in Southeast Asia.
When should I go to hospital with food poisoning?
See a doctor the same day if there is blood in the stool, a high fever, vomiting that stops you keeping fluids down, or signs of dehydration that do not improve with rehydration salts. Call 1669 for confusion, severe pain, breathing problems or vomiting blood.
Can I take loperamide for diarrhea in Thailand?
Ask a pharmacist first. The CDC says medicines of this type are not recommended on their own with bloody diarrhea or with diarrhea and fever, and the NHS says they are not suitable for children under 12.
Sources
- CDC – Yellow Book: Travelers' Diarrhea (chapter dated 24 March 2026) (checked October 2026)
- WHO – Diarrhoeal disease fact sheet (7 March 2024) (checked October 2026)
- NHS – Diarrhoea and vomiting (reviewed 21 December 2023) (checked October 2026)
- UK FCDO – Thailand: health (checked October 2026)