Rifaximin in the UK: the complete access guide
In the UK, rifaximin is not licensed for SIBO or IBS - so the realistic way most people get it for those conditions is off-label, on a private prescription, costing roughly £200-£450 for a two-week course before consultation and testing fees. It is only routinely available on the NHS for a different purpose (liver-related hepatic encephalopathy), started by a specialist. This guide explains the licensing maze, why your GP may hesitate, the NHS and private routes, what it actually costs, and how to have the conversation.
Off-label means not licensed for this use. Using rifaximin for SIBO or IBS in the UK is off-label. That is legal and sometimes appropriate, but it places extra responsibility on the prescriber and means it should be done under proper clinical supervision - not bought and self-dosed. Nothing here is a recommendation to self-treat.
In this guide
The licensing maze (and the brand confusion)
Rifaximin is the same molecule worldwide, but it is sold under different brands at different strengths, and they are licensed for different things. This trips up a lot of articles, so it’s worth getting right:
| Product | Strength | UK licensed use |
|---|---|---|
| Targaxan (also generic “Rifaximin 550 mg”) | 550 mg | Reducing recurrence of overt hepatic encephalopathy1 |
| Xifaxanta | 200 mg | Travellers’ diarrhoea (short course only)2 |
So the 550 mg product used for SIBO (and the dose mirrors the US IBS-D regimen) is branded Targaxan in the UK, not “Xifaxanta” - a common mix-up, since the US brand is “Xifaxan.” Neither UK product is licensed for SIBO or IBS, which is the crux of the whole access problem.
The US-UK gap. In the United States, the FDA approved rifaximin 550 mg for IBS-D in 2015 on the strength of the large TARGET trials.45 The UK never followed with an equivalent licence. The evidence the Americans used exists; the British marketing authorisation for that use does not. That mismatch is why a drug with real trial support is still off-label here.
Why your GP may be reluctant
If a GP hesitates to prescribe rifaximin for your SIBO, it usually isn’t obstruction - it’s a stack of legitimate constraints:
- No UK licence for SIBO/IBS, so prescribing is off-label and the GP personally carries the added responsibility.1
- Cost against tight budgets - at roughly £259 per pack on the NHS list, it’s an expensive drug to prescribe outside its funded indication.6
- Formulary restrictions - many local NHS formularies classify rifaximin as specialist-initiated (“amber”), reserving it for hepatic encephalopathy.10
- A sense that a specialist should decide, particularly without a confirmed breath-test diagnosis.
Understanding this changes the conversation: rather than pushing a reluctant GP, the realistic ask is often either a gastroenterology referral or a private prescription you self-fund.
How to actually get it: NHS vs private
The NHS route is, in practice, limited to hepatic encephalopathy: a hepatologist or gastroenterologist starts and stabilises treatment, and the GP may continue it under a shared-care agreement.310 For SIBO or IBS, NHS funding is inconsistent and often unavailable; where it exists at all, it tends to require a positive breath test and specialist sign-off first.
The private route is how most people obtain it for SIBO. A private GP or gastroenterologist who is satisfied it’s appropriate issues a private prescription, which a pharmacy dispenses; you pay the full cost. It cannot be bought over the counter, and reputable private pharmacies will usually want evidence of a diagnosis (a breath-test result or a consultant letter) before dispensing. This is the path that turns “my GP can’t prescribe it” into a workable option.
What it costs in the UK
| Item | Indicative price | Source |
|---|---|---|
| NHS list price, 56 × 550 mg | ~£2596 | NHS Drug Tariff |
| Per 550 mg tablet (NHS list) | ~£4.60 | Derived |
| Private pharmacy, 56 × 550 mg | ~£400-£420 | Online pharmacy listing |
| Drug only, 14-day SIBO course (42 tablets) | ~£200-£450 | Calculation |
| End-to-end (consult + breath test + drug) | ~£400-£900+ | Estimate |
The headline: the drug itself for a standard two-week SIBO course is broadly £200-£450 privately, but the real-world total usually lands higher once you add a private consultation (often £150-£300) and, if done privately, a breath test (£150-£350). Budget for the whole pathway, not just the tablets. These are indicative figures to help you judge a quote - confirm current prices before committing.
Off-label dosing
The most commonly cited off-label SIBO regimen is rifaximin 550 mg three times daily for 14 days (1,650 mg/day) - the same daily dose the US uses for IBS-D.9 For methane-positive overgrowth (IMO), rifaximin alone tends to underperform, and protocols typically add a second antibiotic (neomycin) under specialist guidance. Exact dose, duration and any combination should be set by your prescriber, not copied from an article - this section is to inform your conversation, not to self-prescribe.
Safety and interactions
Rifaximin’s defining feature is that it is barely absorbed - under about 0.4% enters the bloodstream - so it acts almost entirely within the gut and is generally well tolerated.1 That local action is a large part of its appeal. But “well tolerated” is not “risk-free”:
- Rare but serious skin reactions (including Stevens-Johnson syndrome) have been reported - a severe or blistering rash means stop immediately and seek care.1
- C. difficile infection has been reported with virtually all antibiotics, rifaximin included; new severe diarrhoea during or after treatment needs assessment.1
- Pregnancy: not recommended.1
- Interactions: caution with certain drugs - ciclosporin can markedly raise rifaximin levels, warfarin control (INR) can shift, and effectiveness of low-dose oral contraceptives may be reduced (a barrier method is advised).1
Seek urgent care for a spreading or blistering rash, swelling of the face or throat, breathing difficulty, or severe/persistent diarrhoea. These are not expected effects to push through.
Alternatives
Rifaximin is not the only option, and for some people not the first:
- Herbal antimicrobials performed comparably to rifaximin for SIBO clearance in one (non-randomised) study, with fewer side effects - a reasonable choice where cost or antibiotic avoidance matters.8
- Elemental diet - a demanding but effective two-to-three-week liquid approach.
- Other antibiotics - neomycin (especially for methane/IMO, with rifaximin), metronidazole, or co-amoxiclav, all off-label and specialist-guided.
These are explored in the SIBO pillar and summarised in the treatments hub.
Your GP script
- “My symptoms point towards SIBO. Can I be referred to gastroenterology for a hydrogen/methane breath test?”
- “Is rifaximin for SIBO funded on our local formulary, or is it restricted to hepatic encephalopathy?”
- “If it isn’t available on the NHS for this, would you consider a private prescription so I can self-fund a 14-day course?”
- “Given my other medicines and history, are there interactions or reasons rifaximin wouldn’t be safe for me?”
- “Would a licensed alternative or a dietary approach be sensible to try first?”
References
- Rifaximin 550 mg film-coated tablets (Targaxan), Summary of Product Characteristics. medicines.org.uk (emc), 2025.
- Xifaxanta 200 mg tablets, Summary of Product Characteristics. medicines.org.uk (emc), 2025.
- NICE. Rifaximin for preventing episodes of overt hepatic encephalopathy (TA337). nice.org.uk/guidance/ta337, 2015.
- FDA. Xifaxan (rifaximin) 550 mg supplemental approval for IBS-D, NDA 021361/S-012. accessdata.fda.gov, 2015.
- Pimentel M, et al. Rifaximin therapy for IBS without constipation (TARGET 1 & 2). N Engl J Med. NEJMoa1004409, 2011.
- NHS Drug Tariff, Rifaximin 550 mg tablets (basic price per 56). drugtariffpro.com, accessed May 2026.
- Gatta L, Scarpellini E, et al. Meta-analysis: rifaximin is effective and safe for SIBO. Aliment Pharmacol Ther. PMID 28078798, 2017.
- Chedid V, et al. Herbal Therapy Is Equivalent to Rifaximin for the Treatment of SIBO. Glob Adv Health Med. SAGE, 2014.
- Off-label SIBO dosing reference (rifaximin 550 mg three times daily, 14 days). siboinfo.com (specialist, non-regulatory source).
- North Central London Joint Formulary. Rifaximin (Targaxan) shared-care guideline. nclhealthandcare.org.uk, 2024.
This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.