Irritable bowel syndrome with diarrhea (IBS-D) brings urgent bowel movements, cramping and bloating that can shape every plan you make. Rifaximin, sold in the US as Xifaxan, is one of the few prescription medicines approved specifically for IBS-D. It is also one of the most expensive: a single two-week course of brand-name Xifaxan can cost well over $2,000 in the US without insurance, and no generic is currently sold there. This guide explains how rifaximin works, how it is taken and what to know about generic versions made abroad.
Rifaximin at a glance
| Use (US-approved) | Usual adult dose |
|---|---|
| IBS with diarrhea (IBS-D) | 550 mg three times a day for 14 days; can be repeated up to two times if symptoms return |
| Reducing the risk of hepatic encephalopathy (HE) returning | 550 mg twice a day, long term |
| Travelers’ diarrhea caused by non-invasive E. coli (age 12+) | 200 mg three times a day for 3 days |
How rifaximin works
Rifaximin is an antibiotic that stays almost entirely inside the gut: less than 1% of a dose is absorbed into the bloodstream. It blocks bacterial RNA polymerase, an enzyme bacteria need to make proteins. In IBS-D, the exact way it helps is still being studied, but it appears to change the balance of gut bacteria, including bacteria that may overgrow in the small intestine, and reduce the gas and inflammation that drive bloating and loose stools.
Because so little reaches the rest of the body, rifaximin causes fewer whole-body side effects than most antibiotics and does not interact with as many medicines. Its effect is concentrated where the problem is.
The IBS-D treatment course
The US-approved course is one 550 mg tablet three times a day for 14 days, or 42 tablets in total. It can be taken with or without food. Unlike many IBS medicines, it is not taken every day indefinitely: in clinical trials, many people felt better for weeks after a single course.
If symptoms come back, the label allows up to two further 14-day courses. In the retreatment trial, people who had responded to a first course and then relapsed were more likely to respond again to rifaximin than to placebo. Your doctor will decide whether a repeat course makes sense for you.
Which strength do you need?
Rifaximin tablets come in 200 mg, 400 mg and 550 mg strengths. In the US, IBS-D and HE doses use the 550 mg tablet, and the 200 mg tablet is used for travelers’ diarrhea. The 400 mg strength is common in other countries, including India, where it is used for gut infections and other indications under local guidance. Do not substitute one strength for another without your doctor working out the equivalent dose.
- Rifagut 550 mg: the strength used in the US IBS-D and HE regimens.
- Rifagut 400 mg and Rifaxiheal 400 mg: the strength used in many countries outside the US.
- Rifagut 200 mg: the travelers’ diarrhea strength.
These are Indian generics that contain rifaximin, made and licensed in India.
All the rifaximin tablets we carry, in 200, 400 and 550 mg strengths, are compared with prices on our generic Xifaxan page.
Rifaximin for hepatic encephalopathy
In people with advanced liver disease, toxins made by gut bacteria, such as ammonia, can reach the brain and cause confusion, drowsiness and personality change. This is hepatic encephalopathy. Rifaximin 550 mg twice daily, usually alongside lactulose, reduces the chance of further episodes and of hospital admission. This is specialist treatment that needs regular monitoring and should never be started or stopped without the liver team.
Side effects
Rifaximin is generally well tolerated. In the IBS-D trials, nausea and raised liver enzymes were among the more frequently reported side effects. People taking it for HE more often reported swelling of the ankles, nausea, dizziness, tiredness and fluid in the abdomen, although these are also features of advanced liver disease itself.
Like all antibiotics, it can occasionally allow Clostridioides difficile (C. diff) to overgrow, causing severe, persistent watery diarrhea, sometimes weeks after treatment. Contact your doctor if diarrhea becomes worse, bloody or comes with fever and abdominal pain. Stop and seek help for any allergic reaction, such as rash, swelling or difficulty breathing.
Precautions and interactions
- Not for diarrhea with fever or blood in the stool. Rifaximin does not treat invasive infections like Campylobacter, Shigella or Salmonella.
- Cyclosporine and other P-glycoprotein inhibitors can greatly increase how much rifaximin is absorbed.
- Warfarin: changes in INR have been reported, so blood tests may need to be checked more often.
- Severe liver impairment: more rifaximin is absorbed, so use requires caution.
- Pregnancy: animal studies showed harm to the fetus. Tell your doctor if you are pregnant or planning to be.
Make sure it really is IBS
IBS is diagnosed after other conditions have been ruled out. See a doctor before treating yourself if you have any of these warning signs: symptoms starting after age 45, blood in your stool, unexplained weight loss, anemia, diarrhea that wakes you at night, or a family history of colon cancer, inflammatory bowel disease or celiac disease. Your doctor may suggest blood tests, a stool test or a colonoscopy.
Beyond medicine
Rifaximin works best as part of a wider plan. A low-FODMAP diet, tried with a dietitian’s support, helps many people with IBS-D identify trigger foods. Regular meals, limiting caffeine and alcohol, soluble fiber, stress management and gut-directed therapies can all reduce flare-ups. Keep a symptom diary for a few weeks; patterns often become clear.
Frequently asked questions
How quickly does rifaximin work for IBS-D?
Some people notice less bloating and urgency within the first week. The trials measured the response over the weeks after the 14-day course.
Is rifaximin the same as Xifaxan?
Xifaxan is the US brand name of rifaximin. Generic versions made in other countries contain the same active ingredient.
Can I drink alcohol while taking rifaximin?
There is no known direct interaction, but alcohol can worsen IBS symptoms and harms the liver, which matters for anyone taking rifaximin for liver disease.
Will it affect birth control?
Because so little is absorbed, rifaximin is not expected to reduce the effect of hormonal contraceptives, but ask your doctor or pharmacist about your specific method.
This article gives general information and does not replace advice from your doctor. Diarrhea with fever, blood or severe pain needs medical assessment.