Oregano Oil for SIBO: Does It Really Work?

What SIBO Is And Why It’s Hard To Treat

What is SIBO?

If you are reading this article, then I’m sure you’ve heard the term “SIBO” before. SIBO stands for small intestinal bacterial overgrowth. It occurs when the concentration of bacteria in the small intestine exceeds the normal range.

When there are excessive amounts of bacteria in the small intestine, our body has to compete with bacteria for the food that we eat. These bacteria also have access to undigested food earlier than they are supposed to, which leads to excessive fermentation and gas formation.

Per the Mayo Clinic, the following are common symptoms of SIBO (1):

• Loss of appetite
• Abdominal pain
• Nausea
• Bloating
• An uncomfortable feeling of fullness after eating
• Diarrhea
• Unintentional weight loss
• Malnutrition

To be clear, SIBO is not an infection. The bacteria that overgrow in the small intestine are not pathogenic in nature. They are simply the normal bacteria that are supposed to be in our large intestine. Instead, they have migrated north into the small intestine, where they should not be.

SIBO can be caused by a variety of causes, including but not limited to poor GI motility, viruses, autoimmunity, antibiotics, constipation, low immunity, physical abnormalities, and low stomach acid.

Why conventional treatments fall short

Rifaximin, AKA Xifaxan, is the leading antibiotic for treating SIBO. It is a great option for SIBO because it is not absorbed into the bloodstream, it does not appear to kill beneficial bacteria, and it has a success rate of about 71% (2,3).

However, Rifaximin does not cure every case of SIBO, and it can be incredibly expensive if not covered by insurance. Since 45% of cases of SIBO recur, many people are left wanting alternative options to antibiotics like Rifaximin (4).

Why herbal antimicrobials like oregano oil are gaining attention

For all the reasons above, antimicrobial herbs like oregano have gotten a lot of attention for their potential to treat SIBO. People who relapse frequently can become tired of going back to the doctor to take a SIBO test and start on another round of antibiotics.

Many people would rather order a natural product, like oregano oil, online and take it to treat their recurrent SIBO symptoms from home. 

Herbal antimicrobials are very popular, affordable, and seen as more natural, safer alternatives to antibiotics. Though there is some truth to this, we must be careful to recognize that “natural” does not equal “safer”. This is known as the appeal to nature fallacy.

Certain natural remedies can be harsher, more toxic, and less effective than conventional pharmaceuticals. This is why we must pay close attention to what the scientific literature is saying.

Oregano Oil 101: What Makes It Antimicrobial?

Alright, it’s time to dive into the science to see if oregano oil is all that it is hyped up to be. 

Carvacrol and thymol: the active compounds

Oregano oil is a highly refined and concentrated substance extracted from the aerial components of the oregano plant. It contains certain volatile compounds that give oregano its characteristic scent.

Though there are many compounds present in oregano oil, the most studied and famous are carvacrol and thymol (4).

Carvacrol is the primary active compound in oregano oil, known for its potent antimicrobial effects by disrupting bacterial cell membranes and inhibiting biofilm formation.

Thymol is a secondary phenolic compound in oregano oil that enhances antimicrobial action and provides antioxidant and anti-inflammatory support within the gut.

Together, these antimicrobial compounds make oregano oil an enticing substance for killing off bacteria within the digestive tract.

How oregano oil affects bacteria

Due to the chemical composition of oregano oil, there has been a lot of research surrounding its use as an antimicrobial agent. However, most of this research has been in vitro or in animal models.

Antimicrobial, antifungal, antiparasitic properties

Oregano oil has been studied for its broad-spectrum activity against bacteria, fungi, parasites, and even some viruses. It’s especially well-documented for its antifungal effects against Candida albicans and antiparasitic action against Giardia in laboratory settings (5,6)​​.

This wide-reaching impact is why it’s often used in gut protocols when multiple types of pathogens are suspected.

Disrupts membrane integrity, metabolism, and biofilms

Carvacrol and thymol can damage the protective outer membranes of microbes, increasing their vulnerability to destruction. They also interfere with energy metabolism inside the cell, essentially disrupting vital processes that keep the organism alive​ (7).

Oregano oil has also shown the ability to disrupt biofilms—protective layers that bacteria use to hide from the immune system or treatment (8)​. Read this article I wrote about biofilms to learn more about why this is so important.

Effective against both Gram-positive and Gram-negative bacteria in some studies

Unlike many antibiotics, oregano oil has demonstrated activity against both Gram-positive (like Staphylococcus aureus) and Gram-negative (like E. coli) bacteria in vitro​ (9). This makes it a potentially useful option for mixed overgrowth situations, such as SIBO, where multiple bacterial types are often involved.

That said, most of this research comes from lab-based studies—not clinical trials—so real-world outcomes may differ.

Why formulation matters

Not all oregano oil supplements are created equal. The form it comes in can dramatically impact how well it works and how well your gut tolerates it. 

Free oil (especially liquid drops) is highly volatile and can irritate the lining of your stomach or esophagus. Many people report burning, reflux, or nausea when using uncoated forms, especially on an empty stomach. 

Enteric-coated or microencapsulated capsules are designed to bypass the stomach and release the oil in the small intestine, right where SIBO occurs. This reduces the risk of GI discomfort and may increase effectiveness by delivering the active compounds closer to the overgrowth site​ (10).

The Research Behind Oregano Oil: What Do We Really Know?

Evidence That Supports Its Use

Although oregano oil is often promoted for gut health, most of the evidence we have comes from lab studies or animal models, not large human trials. That said, some of the findings are genuinely promising.

It’s highly effective against Candida albicans, especially when it comes to disrupting virulence factors like biofilm formation, phospholipase production, and germ tube development. These are key survival tools for fungal pathogens, and oregano oil interferes with them at surprisingly low concentrations​ (11).

Oregano-thyme oil blends (like HerbELICO®) have also shown activity against Helicobacter pylori, the bacteria linked to ulcers and acid reflux. In one small human case series, 90% of participants eradicated H. pylori after 45 days of use​ (12).

Perhaps most interestingly, oregano oil may spare beneficial bacteria like Lactobacillus when microencapsulated. A 2024 study using keratin-encapsulated oil showed complete inhibition of Candida while leaving probiotic strains intact​ (13).

This lines up with oregano’s broad antimicrobial and antifungal properties, which are well-documented in vitro. It can disrupt microbial membranes, inhibit metabolism, and interfere with the formation of biofilms, making it harder for pathogens to hide or persist​​.

Gaps and Contradictions in the Research

No human studies directly test oregano oil in diagnosed SIBO patients.

While oregano oil is often included in functional medicine protocols for SIBO, its use is based on in vitro and animal studies targeting specific pathogens like Candida albicans or H. pylori, not the mixed overgrowth patterns seen in SIBO. To date, there are no clinical trials evaluating oregano oil’s effectiveness for SIBO diagnosis or eradication.

Animal studies show molecular activity, but unclear clinical relevance.

In pig models, oregano essential oil altered gene expression related to immune function and intestinal integrity, suggesting biological activity. But, these changes did not translate into clear improvements in health, growth, or gut function​ (14).

Results vary dramatically depending on the oil’s source, formulation, and dose.

The efficacy and safety of oregano oil depend on:

• The species of oregano used (e.g., Origanum vulgare vs. Origanum compactum)
• The extraction method (steam-distilled vs. solvent-extracted)
• The concentration of key compounds like carvacrol and thymol
• The delivery system (liquid drops vs. enteric-coated capsules vs. microencapsulation)
  

These variables make it difficult to apply results from one study to over-the-counter supplements that may be entirely different in potency or absorption.

Can Oregano Oil Treat SIBO? What the Experts Say

The answer is that we really don’t know yet. There are no studies answering this question. Oregano oil is clearly antimicrobial in certain contexts, but it is unclear whether it is capable of treating SIBO as a stand-alone or complementary agent.

Why some protocols include it

There is no clear answer to this question. It is likely a combination of historical use, practitioner popularity, and the limited animal and in vitro data. Unfortunately, it is not uncommon that functional practitioners use treatments just because other practitioners are also using them.

There is also data that certain herbal combination products that contain oregano as one of the ingredients can successfully treat SIBO. Biocidin, for example, is an herbal SIBO treatment that contains oregano oil as one of its many ingredients. Research shows a Biocidin protocol to be successful in treating SIBO (15).

The plural of anecdote is not data

I know a lot of people will self-prescribe oregano oil when they feel bloated and will report it fixing all their problems. I just want to remind you that these are anecdotes, not data. Anecdotes are subjective stories and do not tell us if something is safe or effective.

That doesn’t mean they’re meaningless! Many valuable discoveries in medicine start with patient stories. But anecdotes are limited. They don’t control for placebo, dosing, other lifestyle changes, or long-term effects. Just because something worked for someone doesn’t mean it will work the same way for everyone or that it won’t cause harm.

Anecdotes can point us in a direction, but they can’t replace well-designed studies when it comes to making informed health decisions. Especially with something as potent as oregano oil, it’s important to move beyond testimonials and understand the full picture.

When it might help—and when it might not

Oregano oil can be a useful tool in the right context, but it’s not a universal fix.

It might help in cases of mild to moderate SIBO, especially if there’s suspected fungal overgrowth or a history of poor tolerance to antibiotics. Oregano oil may also be helpful when used short-term to disrupt biofilms or reduce microbial load as part of a broader strategy.

It might not be enough in more complex cases, like methane-dominant SIBO, where research suggests allicin, berberine, and neem may be more effective. (You can read more on that in my Allicin for SIBO blog post.)

It may still play a role in more complex cases, but it’s unlikely to be effective as a stand-alone solution if you’re dealing with long-standing gut issues, biofilm buildup, or hydrogen sulfide-type SIBO. These situations often involve multiple layers of dysfunction that require a more thoughtful, individualized approach.

If any of that sounds familiar, I encourage you to check out my posts on biofilm strategies and how to approach H2S SIBO—they go deeper into the kind of nuanced support these cases tend to need.

Potential Risks and Side Effects of Oregano Oil

Gut irritation and nausea

The most common side effects I’ve seen and heard from clients are gut irritation, reflux, and nausea, particularly when oregano oil is taken in liquid form or on an empty stomach. These reactions are likely due to the high volatility of its essential oil components, especially carvacrol.

Impact on gut microbiome balance

Oregano oil is a broad-spectrum antimicrobial, which means it doesn’t discriminate much between the “bad” bugs and the helpful ones. While a few studies (especially using encapsulated forms) suggest it may spare Lactobacillus​, there’s no guarantee this holds true across all products or doses (16).

Who should avoid it?

Certain populations should be especially cautious with oregano oil—or avoid it altogether:

• People with ulcers, gastritis, or sensitive GI tracts, as the oil may worsen irritation.
  
• Pregnant or breastfeeding individuals, since oregano oil’s safety hasn’t been established in these groups.
  
• Anyone on medications like blood thinners or diabetes medications, as oregano oil may interact with drug metabolism

Should You Try It? Here’s What to Consider

Safe usage: dose, duration, and form

To be transparent, I don’t regularly use oregano oil in my practice, and I never use it as a standalone treatment.

There’s no solid data showing that oregano oil is safe or effective for treating SIBO. But, there’s also no strong data saying it’s harmful. Most people use it for 4–6 weeks, following the instructions on supplement labels.

If you choose to try it, use a third-party tested brand to avoid contaminants and adulterants. Enteric-coated capsules are better tolerated than drops, and it’s wise to rotate herbs rather than using one consistently.

When to use oregano oil vs. investigating deeper

If your symptoms return after using oregano oil, or if it only gives partial relief, that’s a sign there’s more going on. You may need to assess motility, biofilm presence, fungal involvement, or the specific SIBO subtype, which may require a more nuanced approach.

Oregano oil can sometimes play a role, but it’s rarely the full solution. In my opinion, the best outcomes come from looking deeper and treating the root causes, not just suppressing symptoms with herbs.

Bottom Line: A Promising Tool—But Not a Silver Bullet

Oregano oil is a compelling antimicrobial with real potential, but when it comes to treating SIBO, the evidence is still limited. While it may offer short-term symptom relief for some, it’s rarely effective as a stand-alone solution.

SIBO isn’t one-size-fits-all. The type of gas produced, the severity of overgrowth, and the underlying root causes all influence what kind of treatment will actually work and for how long. That’s why personalization matters.

As a functional dietitian, I combine both conventional and functional medicine principles to get to the root of symptoms. If you’re tired of guessing your way through gut protocols, I’m here to help you build a plan that actually fits your body.

Book a discovery call today to see how I can help you on your journey.