Xifaxan (rifaximin) is a prescription antibiotic used to treat three gut-related conditions: traveler’s diarrhea, a liver complication called hepatic encephalopathy, and irritable bowel syndrome with diarrhea (IBS-D). What makes it unusual among antibiotics is that it barely enters your bloodstream. It stays almost entirely in your digestive tract, killing or slowing bacteria right where the problem is. That targeted action is the reason it works for such different conditions and why it tends to cause fewer body-wide side effects than traditional antibiotics.
How Xifaxan Works in the Gut
Xifaxan is classified as a nonsystemic antibiotic, meaning the vast majority of each dose passes through your intestines without being absorbed into your blood. It kills bacteria by latching onto a specific part of their cellular machinery and blocking them from making the RNA they need to survive and reproduce. Because so little reaches the rest of your body, it doesn’t interfere with most other medications. Lab studies confirm it does not inhibit any of the major liver enzymes responsible for processing common drugs, including birth control pills and many widely prescribed medications.
Hepatic Encephalopathy
Hepatic encephalopathy is a condition that develops when a damaged liver can no longer filter toxins, especially ammonia, from the blood. Those toxins reach the brain and cause confusion, forgetfulness, personality changes, and in severe cases, loss of consciousness. It most commonly affects people with cirrhosis.
Xifaxan works here by reducing the population of ammonia-producing bacteria in the intestines, lowering the toxic load your liver has to handle. The standard regimen is one 550 mg tablet twice a day, taken on an ongoing basis to prevent episodes from returning. Most patients also take lactulose, a laxative that further helps clear ammonia from the gut.
Clinical trial data shows the combination is significantly more effective than lactulose alone. Across all stages of liver disease, Xifaxan reduced the risk of a breakthrough episode by 56% to 66% compared to placebo. Among patients with moderate liver impairment, about 23% on Xifaxan experienced a recurrence versus 44% on placebo. For those with more advanced disease, the gap was even wider: roughly 29% versus 64%. These reductions also translated into fewer hospitalizations, which is a major benefit given how disruptive and dangerous severe episodes can be.
Irritable Bowel Syndrome With Diarrhea (IBS-D)
Xifaxan is one of the few antibiotics approved specifically for IBS-D, a condition characterized by recurring abdominal pain, bloating, and loose or urgent stools. The exact role bacteria play in IBS-D isn’t fully understood, but an overgrowth or imbalance of gut bacteria is thought to contribute to symptoms in many patients.
For IBS-D, the treatment course is shorter and higher-dose: one 550 mg tablet three times a day for 14 days. Unlike hepatic encephalopathy, you don’t stay on it continuously. If symptoms come back after a round of treatment, you can repeat the same 14-day course up to two additional times. Many people experience meaningful relief during or shortly after a treatment cycle, though the benefits don’t always last permanently.
Side effects in IBS-D trials were minimal. The only adverse reaction that occurred more often in treated patients than in the placebo group was nausea, affecting about 3% of patients on Xifaxan versus 2% on placebo. That’s a remarkably slim difference, which reflects the drug’s gut-limited activity.
Traveler’s Diarrhea
Xifaxan’s original FDA-approved use was for traveler’s diarrhea caused by certain bacteria, particularly noninvasive strains of E. coli that are the most common culprit in travel-related illness. It is not effective against diarrhea caused by viruses or parasites, so it won’t help with every case you might pick up abroad. The treatment course for traveler’s diarrhea is typically shorter than for IBS-D, usually lasting about three days. In clinical trials, headache was the only side effect that appeared at a notable rate, and it occurred almost as often in the placebo group (9%) as in patients taking the drug (10%).
Off-Label Use for SIBO
Small intestinal bacterial overgrowth, commonly called SIBO, is one of the most frequent off-label reasons doctors prescribe Xifaxan. SIBO happens when bacteria that normally live in the large intestine colonize the small intestine, causing bloating, gas, diarrhea, and sometimes nutritional deficiencies. Because Xifaxan concentrates in the gut and has broad antibacterial activity, it’s a natural fit for this condition even though it doesn’t carry formal FDA approval for it.
A meta-analysis of available studies found that rifaximin eradicated SIBO in about 73% of patients. However, recurrence is common. One study tracking patients after a two-week course found that about 84% of initial responders experienced symptom recurrence within 18 weeks, with the average time to relapse being roughly three months. This is why some patients end up doing multiple treatment cycles or combining Xifaxan with dietary changes to manage SIBO long-term.
Side Effects Across Uses
For short-term uses like IBS-D and traveler’s diarrhea, Xifaxan is remarkably well tolerated. Nausea and headache are the most commonly reported issues, and they barely exceed placebo rates.
The side effect profile looks different for hepatic encephalopathy, but that’s largely because those patients have advanced liver disease and are already dealing with significant health challenges. In the six-month trial for this use, the most frequently reported reactions included swelling in the extremities (15% on Xifaxan vs. 8% on placebo), nausea (14% vs. 13%), dizziness (13% vs. 8%), and fatigue (12% vs. 11%). Joint pain, itching, and fever each affected 5% to 9% of patients. Many of these overlap with symptoms of liver disease itself, making it difficult to separate drug effects from disease effects.
Xifaxan is contraindicated only in people with a known allergy to rifaximin or other drugs in the rifamycin family of antibiotics.
Cost and Generic Availability
Xifaxan is expensive, often costing over $1,500 for a single 14-day course without insurance. A generic version does not yet exist on the U.S. market. In early 2025, the FDA granted tentative approval to a generic rifaximin 550 mg tablet from Amneal Pharmaceuticals, but that approval is on hold due to patent litigation with Xifaxan’s manufacturer. A 30-month legal stay was triggered when the lawsuit was filed in 2024, which means a generic likely won’t be available for at least a couple of years. In the meantime, manufacturer savings programs and insurance coverage are the main ways patients manage the cost.