A common question Dr. Patrick Nemechek hears is: how can you know how to treat small intestinal bacterial overgrowth (SIBO) if you don’t do a breath test to determine whether hydrogen or methane is present?
In this video, Dr. Nemechek lays out a practical, physiology-based rationale for management that he uses in his clinic. He explains why he often does not rely on breath testing, how he thinks about hydrogen- versus methane-associated patterns, and why rifaximin is frequently his starting point.
Educational disclaimer: This article summarizes a clinical discussion from Dr. Nemechek’s video and is for education only. It is not medical advice and is not a substitute for diagnosis or treatment by your clinician. Medications and antibiotics have risks and must be prescribed and supervised by a licensed professional.
Why Dr. Nemechek often does not rely on SIBO breath tests
Dr. Nemechek says one reason he doesn’t routinely use breath testing is that, in his words, the tests are “notoriously inaccurate.” He adds a practical point: for his approach, the exact breath test pattern frequently doesn’t change what he does first.
In his clinical framing, breath tests can be wrong “20–30% of the time,” and he has seen patients who were breath test negative, could not get treated, but then improved after being prescribed rifaximin.
How he explains hydrogen vs. methane patterns in overgrowth
Dr. Nemechek describes the gut as having “families” of bacteria that normally occupy different regions. In overgrowth, he explains, “normal bacteria” are present in the wrong place—higher up in the small intestine.
He then distinguishes between two broad situations:
1) Bacterial overgrowth without methane
In the framework he describes, if bacteria are overgrowing in the small intestine, that corresponds to a breath test pattern he refers to as “hydrogen positive, methane negative.”
2) Methane production and the role of “ARA” organisms
Dr. Nemechek also discusses a group he calls “ARA,” which he describes as very primitive forms of bacteria (and notes they are often thought of separately). In his explanation, when these organisms are present “up here” (in the small intestine) in addition to bacterial overgrowth, methane is produced.
He describes methane as having an “anesthetic kind of an effect” on the intestinal tract and says it can slow intestinal movement in a significant way.
Why severe constipation raises his suspicion for methane-associated overgrowth
Referencing a paper he mentions (with links provided in the original video description), Dr. Nemechek explains that a “methanogen overgrowth” refers to an ARA-type organism producing methane. In his clinical interpretation, these are the people with the most severe constipation.
He emphasizes the pattern he’s watching for is not just any constipation or intermittent constipation, but “really, really bad constipation,” which makes him suspect a methane-overgrowth case.
Rifaximin as a practical “go-to” in his discussion
Dr. Nemechek notes that clinicians have dealt with intestinal overgrowth issues for decades, particularly in adults with severe liver disease. In that setting, he states rifaximin is a “go-to drug” around the world.
He also explains the common idea many doctors discuss: using one antibiotic to treat bacteria (he names rifaximin as an example) and another antibiotic (he names metronidazole or neomycin) to treat methane-producing organisms.
Why he often does not start with combination therapy
Dr. Nemechek says that, in the vast majority of cases, adding additional antibiotics specifically for methane producers is not necessary. He describes other studies he references as showing “almost no difference” in outcomes between treating methane-producing overgrowth with rifaximin alone versus rifaximin plus neomycin.
Based on that, he explains why he doesn’t feel he must know in advance—via breath testing—whether he “needs combination or just rifaximin alone,” because rifaximin “seems to be able to take care of it on its own” in most cases.
The outlier scenario: when he considers adding another antibiotic
Dr. Nemechek adds an important nuance: it isn’t 100%.
He says that on occasion—“very infrequent”—he sees someone with very bad constipation who improves significantly on rifaximin but is not “all the way better,” with constipation still prominent. In those cases, he has sometimes needed to add neomycin or metronidazole. He notes a preference for neomycin in this context because, in his experience, it “makes people less nauseated.”
His main takeaway: don’t get hung up on the breath test
Dr. Nemechek’s bottom line is straightforward: don’t get stuck on needing a breath test to move forward, especially given his concern about inaccuracy. He encourages viewers who are worried they have SIBO to talk with their primary doctor about it and discuss treatment options.
He also remarks that in the U.S., rifaximin’s brand name is Xifaxan, and he has heard that some patients whose insurance won’t cover it obtain it through Canadian mail order.
Finally, he describes rifaximin’s role in a very practical way: in his explanation, rifaximin is used to take an “overgrowth” state and turn it back toward a more normal distribution. He comments that people may label the condition differently (for example, IBS with diarrhea, hepatic encephalopathy, or SIBO), but the central point in his discussion is that rifaximin is aimed at improving the overgrowth pattern he described.
