SuppleGut Take the quiz

Western herbalism

OreganoOriganum vulgare

Culinary herb sold as a concentrated oil. One uncontrolled 14-person study cleared some gut parasites on 600 mg a day; the rest is laboratory or animal work.

Botanical name
Origanum vulgare
Part used
leaf and flowering top; the essential oil is steam-distilled from them
Also called
Oil of oregano, Wild marjoram, Mediterranean oregano, Mexican oregano (a different plant, Lippia graveolens, sometimes sold as oregano)
Used in
Western herbalism
Taken for
Antimicrobial use
Sold as
capsules, tincture, tea, fresh

The plant

Oregano is a Mediterranean mint-family herb, Origanum vulgare, used for centuries in cooking. The leaves and flowering tops are dried for tea and seasoning, and the aromatic oil is steam-distilled from them. Supplements called oil of oregano are that essential oil, usually diluted in a carrier oil or an emulsion and sold in capsules or drops. Products labeled oregano can come from several Origanum species, and other plants such as Mexican oregano (Lippia graveolens) are also sold under the same word.

The oil is rich in two phenols, carvacrol and thymol. One commercial gut formula described in a published study listed its oregano oil as providing 55 to 75 percent carvacrol and its red thyme oil as providing 30 to 50 percent thymol. The share varies by species, soil and distillation method, so a bottle’s strength cannot be read from the word oregano alone.

In gut supplements the oil is included for its laboratory antimicrobial activity, often alongside other oils, berberine plants and bitter herbs, which makes it hard to say which ingredient a trial result belongs to.

How the traditions use it

Western herbalism

Oregano is a staple of Mediterranean cooking, and Leyva-López and colleagues describe oregano species from Turkey, Algeria, Jordan, Mexico and elsewhere that are used in folk medicine. We found no European or WHO monograph that approves oregano or its oil for a gut complaint, so the digestive use rests on folk tradition and laboratory work rather than on a regulator’s review.

What is in it

The main active constituents are carvacrol and thymol, with p-cymene and gamma-terpinene as common companions. Leyva-López and colleagues review laboratory findings that oregano oils inhibit bacteria, fungi and viruses and act as antioxidants. In a mouse model of Campylobacter infection, carvacrol lowered bacterial counts in the ileum and eased diarrhea. A published oil mixture of savory, oregano and thyme inhibited 20 Helicobacter pylori strains in a dish at 4 to 5 percent by volume. All of this is test-tube or animal work, and none of it shows the same effect in a human gut.

What the human trials show

The human evidence is very thin. The most cited study is Force and colleagues, who gave 14 adults with enteric parasites in their stool 600 mg of emulsified oil of oregano daily for 6 weeks. Afterward Entamoeba hartmanni had disappeared in four people, Endolimax nana in one, and Blastocystis hominis in eight; Blastocystis scores fell in three more, and symptoms improved in 7 of the 11 who had tested positive for Blastocystis. It was a small report with no control group, so a natural clearing of these organisms cannot be ruled out.

Ghitea and colleagues studied 106 people with metabolic syndrome, using an oregano essential oil as an antibacterial treatment for minor staphylococcal, E. coli and streptococcal infections and setting it against antibiotic treatment. After a 10-day course they reported an antibacterial effect, no intestinal side effects, and a better phase angle. This was a study of infections in people with a metabolic condition, not of a gut disorder.

Chedid and colleagues compared two commercial herbal formulas with rifaximin for small intestinal bacterial overgrowth in a retrospective clinic series: 17 of 37 people (46 percent) on herbal therapy had a negative breath test after 4 weeks, against 23 of 67 (34 percent) on rifaximin, a difference that was not statistically significant. One formula contained oregano oil among many other herbs, so the result cannot be credited to oregano.

Missing from the record: a randomized, placebo-controlled trial of oregano oil for parasites, bacterial overgrowth, candida or any other gut outcome, and any dose-finding study.

StudyDoseWhat it found
Uncontrolled study, 14 adults with enteric parasites in stool PMID 10815019600 mg emulsified oil daily for 6 weeksE. hartmanni gone in 4, Endolimax nana in 1, Blastocystis in 8; symptoms improved in 7 of 11 Blastocystis-positive people
Study in 106 people with metabolic syndrome and minor infections; oregano oil as antibacterial treatment, set against antibiotics PMID 3342999110-day course (amount not given in the abstract)Antibacterial effect reported, no intestinal side effects, improved phase angle
Retrospective series, 104 people with SIBO; herbal formulas (one with oregano oil among many herbs) versus rifaximin PMID 248919902 capsules twice daily for 4 weeks (commercial formulas)Negative breath test in 17 of 37 (46%) on herbals versus 23 of 67 (34%) on rifaximin; not significant (P=0.24)

How much the studies and the texts used

Force and colleagues used 600 mg of emulsified oil of oregano a day for 6 weeks. The Chedid series used commercial formulas of 2 capsules twice daily for 4 weeks, and the oregano oil in them was one component of a blend. We found no dose tested in a randomized trial. Oil of oregano is far stronger than the leaf: the traditional preparation is dried leaf as a seasoning or a tea, and no source we read gives a standard tea amount.

Doses here describe what studies and pharmacopoeias used. They are not a recommendation for any person; a clinician or pharmacist who knows your medicines and conditions is the right person to ask.

Side effects and cautions

We found no published safety review of oral oregano oil in people. In the studies above, Ghitea and colleagues reported no intestinal side effects over 10 days, and Chedid and colleagues recorded one case of diarrhea in the herbal arm compared with several adverse events in the rifaximin arm, but none of these studies was built to measure safety. Several different plants are sold as oregano, so the labeled species matters when reading any report. We found no human data on use in pregnancy, breastfeeding or children.

Interactions

We found no published interaction study of oregano oil with medicines in people. The Chedid series recorded adverse effects but was not designed to look for interactions. Products that combine oregano oil with berberine plants, wormwood or goldenseal inherit the interaction record of those ingredients; check the other herbs on the label rather than assuming the oil is the only active part.

Medicines the quiz checks oregano against

When a quiz taker names one of these medicines, the rule below fires. Each comes from a published interaction reference; none is a diagnosis:

Oregano on the shelf: the products that contain it

The products here name oregano among their actives. How much of it a serving holds, and whether that matches any trial, is on each page.

Gaia Herbs Oil of Oregano 4.7 out of 5 from 6,891 ratings from Amazon · $0.93 a day Biocidin Botanicals Biocidin Broad-Spectrum Liquid Formula 4.5 out of 5 from 1,079 ratings from Amazon · ~$1.41 per day at the full 15-drop dose

Is a oregano product right for you?

Three minutes, no sign-up: the quiz turns your symptoms and routine into one named product and says why.

Take the quiz

Often paired or compared

Ayurvedic / TCM / Western Clove Syzygium aromaticum Ayurvedic / TCM / Western Garlic Allium sativum TCM / Western Berberine Berberis, Hydrastis, Coptis and Mahonia species (source plants) Western Black walnut Juglans nigra

Questions people ask

Is there a human trial showing oil of oregano kills gut parasites?

One 14-person study with no control group gave 600 mg a day for 6 weeks and found that several organisms, including Blastocystis hominis in eight people, had cleared from the stool afterward. We found no randomized, placebo-controlled trial. Nothing larger has been published that we could find.

Does oil of oregano treat small intestinal bacterial overgrowth?

A retrospective clinic series found a negative breath test in 17 of 37 people (46 percent) on herbal formulas against 34 percent on rifaximin, not a significant difference. One of the formulas contained oregano oil among many other herbs, so the result cannot be attributed to oregano.

What is the difference between oregano leaf and oil of oregano?

The leaf is the culinary herb, used in food and tea. The oil is the steam-distilled essential oil, a concentrated liquid rich in carvacrol and thymol. Studies of the oil do not tell you what the leaf does.

Do laboratory results mean it works in people?

Not by themselves. Oregano oil inhibits bacteria and fungi in a dish, and carvacrol eased diarrhea in infected mice, but we found no controlled human trial showing that those results carry over to people.

Sources