Can Antibiotics Cause Diarrhea and How to Stop It

Clinically reviewed by Dr. Ponlawat Pitsuwan, Physician, Doctor Samui. Last reviewed: August 2026

You came to Koh Samui, picked up an infected reef cut near Chaweng or a chest bug that wouldn’t shift, and the clinic gave you antibiotics. Two days in, you are running to the bathroom more than before. The medication that was supposed to fix things seems to be making your stomach worse.

It can. Antibiotics cause diarrhea in a significant number of people who take them. Mild cases usually settle without much intervention. But in Samui’s heat and humidity, dehydration moves fast, and a few warning signs mean you should not wait things out alone.

Why Antibiotics Cause Diarrhea

Your gut holds billions of bacteria, most of them harmless or actively helpful. Antibiotics cannot tell the difference between the bacteria causing your infection and the ones keeping your digestion stable. They disrupt both. That disruption throws your gut out of balance, causing it to move contents through faster and absorb less water along the way. The result is loose, frequent stools.

This is called antibiotic-associated diarrhea, and it is a recognised side effect. In most cases it does not mean something has gone seriously wrong.

Which Antibiotics Are Most Likely to Cause It

Broad-spectrum antibiotics carry the highest risk. They are designed to work against a wide range of bacteria, which means they affect a wider range of gut bacteria too.

The antibiotics most commonly prescribed on Koh Samui for wound infections, chest infections, and waterborne illness include amoxicillin-clavulanate, clindamycin, cephalosporins, azithromycin, and ciprofloxacin. Here is the irony: azithromycin and ciprofloxacin are also among the most commonly used treatments for traveller’s diarrhea on the island. They can treat the diarrhea you came in with while triggering a new round of it from gut disruption. If your symptoms started or worsened after beginning one of these, that is likely why.

Mild vs. Serious Antibiotic Diarrhea — Knowing the Difference

Most antibiotic diarrhea is mild. Loose stools two to four times a day, no fever, no blood, settling within a few days.

The concern is C. diff, short for Clostridioides difficile. This is a bacteria that can overgrow when your normal gut bacteria are knocked back by antibiotics. It produces toxins that inflame the gut lining, sometimes severely, and it does not go away on its own.

If you see any of the C. diff warning signs, stop waiting and get assessed. Treatment requires specific antibiotics, and it is very different from managing ordinary antibiotic diarrhea.

Dehydration Risk in Koh Samui’s Heat

Generic health advice does not account for this. In Samui’s climate, high heat and high humidity year-round, your body loses fluid faster than it would at home. Add diarrhea on top of that and dehydration can set in within hours.

Patients come into our Chaweng clinic after managing diarrhea in their hotel room, drinking water, feeling like they are keeping up, and they are already significantly depleted by the time they arrive. Children are more vulnerable to this than adults, and it escalates quickly. If your child has antibiotic diarrhea on the island and is not keeping fluids down, do not wait until morning.

Watch for these signs: no urination for six or more hours, dry mouth, dizziness when standing, no tears in a crying child, and extreme fatigue. Any of these warrant same-day assessment.

Should You Stop Taking Your Antibiotics?

Do not stop your course without speaking to a doctor first. Stopping early risks leaving the original infection undertreated. It can return, and sometimes it comes back harder.

A doctor can review whether a different antibiotic with a lower gut impact could finish the job, or advise how to manage the side effects so you can complete treatment. That decision depends on your specific infection and your current symptoms. It is not something to settle by searching online at midnight.

How to Manage Mild Antibiotic Diarrhea

If you have loose stools with no fever and no blood, these steps genuinely help.

Stay hydrated. Water alone is not enough when you are losing electrolytes through diarrhea. Use oral rehydration sachets, available at any pharmacy on the island. Sports drinks are a distant second. In Samui’s heat, your fluid needs are higher than the packaging suggests.

Eat plainly. Bananas, rice, and toast are a reasonable short-term approach. Avoid dairy, high-fibre foods, alcohol, and heavily spiced food while your gut is recovering.

Take a probiotic. Two specific strains have the best clinical support for reducing antibiotic diarrhea: Lactobacillus GG and Saccharomyces boulardii. Take them at least two hours apart from your antibiotic dose. If you take them together, the antibiotic kills the probiotic before it can work.

Can You Take Imodium While on Antibiotics?

Loperamide, sold as Imodium, can be considered for mild diarrhea with no fever and no blood in your stool. It slows gut movement and reduces stool frequency, and in that setting it is generally safe.

Do not take it if you have a fever, blood in your stool, or any suspicion of C. diff. Slowing gut movement with C. diff traps toxins inside and can make the infection significantly worse. If you are not sure which situation you are in, ask a doctor before taking it.

Antibiotic Diarrhea During a Samui Holiday

This is the scenario we see regularly at our Chaweng clinic. A tourist started antibiotics for an infected snorkeling wound, or for a chest infection picked up on the flight in, and now they have diarrhea mid-holiday and are not sure what to do.

If your diarrhea is mild and you have no red flag symptoms, follow the self-care steps above and continue your antibiotic course. If things are getting worse rather than better after 48 hours, or if you have any of the warning signs from the table above, come in. Doctor Samui offers walk-in consultations at our Chaweng clinic and 24-hour hotel and villa visits across the island. We can assess your symptoms, run a stool test if needed, review your prescription, and provide IV rehydration if you are already depleted. You can read more about how we handle diarrhea treatment on Koh Samui on our dedicated page.

When to See a Doctor — Clear Thresholds

See a doctor the same day if you have a fever above 38.5°C with diarrhea, blood or mucus in your stool, diarrhea that is getting more frequent rather than less, signs of dehydration as listed above, or a child under two years old with diarrhea.

See a doctor within 24 hours if your diarrhea has not improved after 48 hours on the antibiotic, or if it started after you finished the course. Diarrhea that begins days or weeks after your last tablet is a red flag for C. diff and needs a stool test to rule it out.