Oregano

Origanum vulgare L. was named by Linnaeus in Species Plantarum in 1753 and is the accepted name in Kew’s Plants of the World Online (POWO), which places it in the mint family, Lamiaceae, and describes a perennial of the temperate biome used as food and medicine. POWO’s native range runs from Macaronesia to China: the Azores, Madeira, and the Canary Islands, Morocco, Algeria, and Tunisia, nearly all of Europe from Portugal and Ireland to Norway, Finland, and European Russia, then the Caucasus, Iraq, Iran, Central Asia, Afghanistan, Pakistan, the Himalaya, Siberia, China, Taiwan, and Myanmar. It has been introduced to 18 US states, five Canadian provinces, southwestern Mexico, Venezuela, and New Zealand’s South Island. POWO accepts six subspecies: glandulosum, gracile, hirtum, virens, viridulum, and vulgare. Greek oregano, subsp. hirtum, is native to Greece, Crete, the East Aegean islands, Albania, Bulgaria, the northwestern Balkans, Cyprus, and Türkiye. LiverTox gives wild marjoram and winter marjoram as other names for the species.

Nurzyńska-Wierdak and Walasek-Janusz (Pharmaceuticals 2025) describe oregano as a perennial that can exceed 100 cm, with an upright stem that branches toward the top and is sometimes tinged red, and opposite, stalked leaves that are broadly oval to lance-shaped with smooth or finely toothed edges. The whole plant carries glandular hairs and a spicy, thyme-like scent. Numerous small pink, lilac, or white flowers, rich in nectar, open in branched clusters from June to September and draw bees, bumblebees, and butterflies; the medicinal herb is gathered as flowering begins. Several other plants share the name. Turkish oregano, Origanum onites, is native to Greece, Crete, the East Aegean, Sicily, and Türkiye, and the FDA’s spice list still calls it pot marjoram under the old name Majorana onites. Spanish oregano is Thymbra capitata, a Mediterranean member of the mint family that POWO accepts in place of the older names Thymus capitatus and Coridothymus capitatus. Mexican oregano, Lippia graveolens, is in POWO a synonym of Lippia origanoides, a shrub of the verbena family (Verbenaceae) native from Texas and New Mexico through Mexico and Central America to Argentina, and Bautista-Hernández and colleagues (Molecules 2021) note that Poliomintha longiflora, Lippia berlandieri, and Monarda fistulosa var. menthifolia are also sold as Mexican oregano. Trade definitions differ: according to Black and colleagues (Food Chemistry 2016), the European Pharmacopoeia and the European Spice Association accept only O. vulgare subsp. hirtum and O. onites as oregano, while the international standard ISO 7925 allows any Origanum except marjoram, and the FDA’s list of safe spices assigns the name oregano to Lippia species.

Oregano’s chemistry depends on which plant, and which population, is in the jar. Lukas, Schmiderer, and Novak (Phytochemistry 2015) analyzed 502 wild Origanum vulgare plants from 51 populations in 17 European countries and found essential oil contents from 0.03% to 4.6%, with three main chemical types: one built on the cymyl pathway, which yields carvacrol and thymol, one dominated by sabinene compounds, and one by linalool and linalyl acetate. The phenol-rich cymyl type was typical of plants from Mediterranean climates, while sabinene types characterized plants from continental Europe, so wild oregano from a northern meadow may contain little carvacrol. Mediterranean oils are another matter: Anastasiou and colleagues (Molecules 2019) measured 72.0% carvacrol in a Greek oregano oil and 42.0% in a Spanish oregano (Thymbra capitata) oil, and Maral and colleagues (Zeitschrift für Naturforschung C 2021) found 82.1% in a Greek oregano oil. Black and colleagues cite leaf oil contents of about 3–4% for Mexican oregano and 2–2.5% for Mediterranean oregano. LiverTox counts more than 60 constituents in the leaves and flowers, and LactMed lists carvacrol, thymol, eugenol, and rosmarinic acid. Carvacrol and thymol are structural isomers: phenols with the same formula, C10H14O, that differ only in where one group sits on the ring.

Oregano’s name is Greek. Nurzyńska-Wierdak and Walasek-Janusz trace the name Origanum to Hippocrates in the fifth century BC and to the Greek words oros, mountain, and ganos, joy: “joy of the mountains.” The Roman writer Pliny the Elder, in book 20 of his Natural History, wrote that origanum “includes many varieties employed in medicine.” One, called onitis or prasion, was taken with warm water for gnawing pains of the stomach and for indigestion, and in white wine for the stings of spiders and scorpions. Of the Heracleotic origanum, he judged the best to come from Crete and the next best from Smyrna, and the chapter heading counts thirty remedies: it was taken as a diuretic, used for itch, toothache, and bruises, given with honey and salt for the spleen, and employed for repelling serpents. Ancient plant names do not map neatly onto modern species, so Pliny’s origanum cannot simply be equated with today’s Origanum vulgare.

In folk medicine, LiverTox writes, oregano oil has been used for respiratory illnesses and infections, including colds, fever, cough, bronchitis, bacterial and fungal infections, parasites, and urinary tract infections, and LactMed notes its traditional use in Türkiye to increase breast milk. European regulators have acknowledged long use of two relatives but not of oregano itself. EMA’s herbal committee accepts dittany of Crete (Origanum dictamnus) as a traditional herbal tea for cough with a cold and mild stomach complaints, and as a soaked dressing for minor skin inflammation and bruises, and accepts marjoram (Origanum majorana) as a traditional remedy for bloating and flatulence and, as an ointment, for irritated skin around the nostrils. Oregano also had darker uses. Ciganda and Laborde (Journal of Toxicology: Clinical Toxicology 2003) reviewed 86 calls to the Montevideo poison center between 1986 and 1999 about herbal infusions taken to induce abortion; one of the most frequent was Carachipita, an over-the-counter mixture of pennyroyal, oregano, and two other herbs, which was linked to multiple organ failure and one death.

Oregano became an American staple only after World War II. NPR’s food blog The Salt recounts how many US soldiers first tasted it in southern Italy during the 1943–1945 campaign, and cites the food historian John Mariani’s finding that US oregano sales rose 5,200% between 1948 and 1956, with imports reaching 1.5 million pounds a year by the 1960s. Popularity brought fraud: Black and colleagues at Queen’s University Belfast found in 2016 that about a quarter of 78 dried oregano samples bought in shops and online had been bulked out, mostly with olive and myrtle leaves, and passed their results to regulators. Oil of oregano arrived as a supplement; a 2000 study of it for intestinal parasites listed Biotics Research Corporation, a supplement company, among its author affiliations, and LiverTox notes that today’s capsules and oil solutions are advertised for energy and general wellness. The oil is also widely studied as a feed additive for farm animals: in a 2022 systematic review of poultry infection studies, Farinacci and colleagues (Planta Medica) found Origanum vulgare to be the second most frequently tested plant, after sweet wormwood (Artemisia annua).

Carvacrol and thymol are the compounds most credited with oregano oil’s effects, and nearly all the evidence for them comes from laboratories. Sharifi-Rad and colleagues (Phytotherapy Research 2018) attribute carvacrol’s strong antimicrobial activity to its free hydroxyl group, its fat solubility, and its phenol ring, report activity against food-poisoning bacteria such as Escherichia coli, Salmonella, and Bacillus cereus, describe anticancer effects only in preclinical models, and conclude that human trials of carvacrol are still lacking. Lu and colleagues at Massachusetts General Hospital (Frontiers in Microbiology 2018) found that an oregano oil killed 11 multidrug-resistant bacteria taken from wounded soldiers, including MRSA, at 0.08 to 0.64 mg/ml, broke up their biofilms, and visibly damaged bacterial cells under the electron microscope. The bacteria did not become resistant over 20 rounds of exposure. In mice with infected third-degree burns, oil applied to the wound cut bacterial counts about a thousandfold within an hour, and three daily applications at 10 mg/ml caused no skin damage on microscopy.

Such results do not show that swallowing oregano oil treats an infection. Concentrations that kill bacteria in a dish or on a mouse wound are applied directly to the microbes, and we found no human studies of how much carvacrol from an oregano oil capsule reaches the blood, the gut wall, or infected tissue. Animal studies are suggestive at most: Preuss and colleagues (Toxicology Mechanisms and Methods 2005) injected mice with Staphylococcus aureus and found that 6 of 14 given daily oral origanum oil survived 30 days, against 7 of 14 given vancomycin and none of 14 left untreated. When oregano has been tested in people for a laboratory-style effect, results have been modest or null. Nurmi and colleagues (Journal of Agricultural and Food Chemistry 2006) randomized 45 healthy men to juice providing 0, 300, or 600 mg a day of oregano phenolics for four weeks; the phenolics were absorbed and excreted, but blood lipids and markers of oxidative damage to fats (lipid peroxidation) did not change. Reviews of oregano’s antifungal activity, such as Mezzomo and colleagues (Chemistry and Biodiversity 2025), focus on inhibitory concentrations measured against Candida yeasts and molds in the laboratory.

Oregano also contains non-volatile polyphenols, such as rosmarinic acid, and these bind iron. In iron absorption studies using an isotope-labeled iron tag, Brune and colleagues (European Journal of Clinical Nutrition 1989) found that oregano added to a meal inhibited iron absorption in proportion to its content of iron-binding galloyl groups, just as tea did. That is a reason for people with low iron stores to keep concentrated oregano products away from iron supplements and iron-rich meals. Other proposed mechanisms remain speculative. The authors of a 2025 Algerian case report suggested that oregano polyphenols inhibit the liver enzymes CYP2C9 and CYP3A4, which break down many medicines including the blood thinner acenocoumarol, and that carvacrol and thymol have anticoagulant activity, but these ideas rest on laboratory work rather than studies in people. We found no human pharmacokinetic interaction studies of oregano or its oil.

Intestinal parasites and SIBO are the gut uses most often cited for oil of oregano, and the evidence is weak. Force, Sparks, and Ronzio (Phytotherapy Research 2000) gave 600 mg a day of emulsified oregano oil for six weeks to 14 adults whose stools contained Blastocystis hominis, Entamoeba hartmanni, or Endolimax nana. Entamoeba hartmanni disappeared in four cases, Endolimax nana in one, and Blastocystis in eight, with lower Blastocystis scores in three more, and gut symptoms improved in 7 of the 11 people with Blastocystis. There was no comparison group, and the paper lists Biotics Research Corporation, a supplement company, among its affiliations. For SIBO, Chedid and colleagues (Global Advances in Health and Medicine 2014) reviewed the charts of 104 Johns Hopkins patients who chose four weeks of rifaximin, 1,200 mg a day, or one of two herbal capsule regimens. Breath tests turned negative in 17 of 37 on herbs (46%) and 23 of 67 on rifaximin (34%), a difference that was not statistically significant. Only one regimen contained oregano: Candibactin-AR, a capsule combining oregano oil, red thyme oil, sage, and lemon balm, paired with a berberine formula. The authors reported no conflicts of interest and called for prospective trials. Verdict: interesting but unproven, and nothing here isolates oregano.

Colds, sore throats, and coughs are a traditional use, and LiverTox lists them, but no trial has tested oregano or its oil alone for them. The closest is a trial by Ben-Arye and colleagues (Evidence-Based Complementary and Alternative Medicine 2011), who randomized 60 primary-care patients in Israel with upper respiratory infections to a throat spray of five essential oils, from lemon-scented eucalyptus, eucalyptus, peppermint, Syrian oregano (Origanum syriacum), and rosemary, or to a placebo spray, five times a day for three days. Twenty minutes after spraying, the most troublesome symptom, whether sore throat, hoarseness, or cough, eased more with the oils, but the authors found the effect was no longer significant after three days. That spray used a different Origanum species mixed with four other oils. EMA’s monograph for another relative, dittany of Crete, accepts its tea for cough with a cold on the basis of traditional use only. Verdict: no reliable evidence that oregano prevents or shortens colds or flu; thyme combinations and pelargonium have better trial data for acute bronchitis.

Wound care has the best-designed oregano trial, and it is small. Ragi and colleagues (Journal of Drugs in Dermatology 2011) randomized 40 people having surgical skin excisions to a 3% oregano extract ointment or plain petrolatum in an investigator-initiated, double-blind study. On day 12, Staphylococcus aureus grew from 19% of wounds treated with oregano and 41% of those treated with petrolatum, and one person developed cellulitis, a spreading skin infection, against three. Scar color, pigmentation, and pliability were rated better with oregano, but overall scar appearance was equivalent. No larger trial has followed. Other skin claims rest on less. LactMed notes that oregano oil has been advocated for Candida (thrush) infection of the nipples during breastfeeding, but no clinical study has confirmed that it is safe or effective, and a Romanian study by Ghitea and colleagues (Molecules 2021) that treated minor bacterial infections in people with metabolic syndrome with oregano oil had no antibiotic or placebo comparison group. Verdict: one small, encouraging trial of a dilute extract ointment; no evidence for undiluted oil on the skin.

Cholesterol and metabolic health have a few small studies with mixed designs. Ozdemir and colleagues (Journal of International Medical Research 2008) gave 32 Turkish adults with mild high cholesterol 25 ml of a water distillate of Turkish oregano (Origanum onites) after each meal for three months, alongside diet advice, and compared them with 16 people given diet advice alone; LDL cholesterol, lipoprotein(a), and C-reactive protein fell more, and HDL cholesterol and blood vessel function improved more, with oregano. The study was not described as randomized or blinded. Maral and colleagues randomly assigned 34 athletes to Greek oregano, Origanum dubium, or lavender essential oil, or to no oil, for 14 days; HDL cholesterol rose with the two oregano oils, but total cholesterol, triglycerides, and liver tests did not change. In the double-blind juice trial by Nurmi and colleagues, oregano phenolics did not change blood lipids at all. A 2023 scoping review by Mackonochie and colleagues (Nutrients), whose authors include employees of the herbal tea company Pukka Herbs, found no clinical research on culinary amounts of oregano for metabolic syndrome. Verdict: too little to recommend oregano for cholesterol or blood sugar.

The antibiotic-resistance pitch deserves its own caution. Laboratory studies like that of Lu and colleagues are genuinely interesting, and oregano is widely tested in farm animals: a 2026 meta-analysis by Yousfi and colleagues (Avian Pathology) of eight studies in chickens infected with the gut parasite Eimeria found better weight gain and fewer parasite eggs with oregano extracts. But no human trial has shown that oregano oil treats an antibiotic-resistant infection, and using it instead of a prescribed antibiotic can let a serious infection progress. In the kitchen, oregano is a flavorful herb with nothing to prove. Its relative marjoram has its own EMA monograph as a traditional remedy for bloating and flatulence in adults; EMA’s assessment notes that marjoram contains small amounts of hydroquinone derivatives such as arbutin, which led Germany’s Commission E not to recommend oral medicinal use, although EMA judged the exposure from recommended doses to carry negligible risk. Anyone looking for a digestive herb with better evidence will find more on the peppermint and caraway pages.

Oregano comes in four broad forms: the fresh or dried leaf used as a spice; teas and infusions of the herb; the essential oil, distilled from the flowering herb; and branded “oil of oregano” supplements, sold as oil solutions or capsules, some with a stated carvacrol percentage. There is no regulator-approved medicinal dose for Origanum vulgare: EMA has no monograph for it, and LiverTox notes that recommended doses vary widely, partly because products differ in essential oil concentration. Doses in studies were product-specific. The parasite study used 600 mg a day of an emulsified oil for six weeks. In the SIBO chart review, each Candibactin-AR capsule listed 0.1 ml of oregano oil providing 55 to 75% carvacrol, 0.2 ml of red thyme oil, 75 mg of sage extract, and 50 mg of lemon balm extract, and patients took the paired products at two capsules twice a day for four weeks. The wound trial used a 3% oregano extract ointment, the throat-spray trial a five-oil blend applied five times a day, and the Turkish cholesterol study 25 ml of an Origanum onites distillate after each meal.

Quality is a real problem for both the spice and the supplement. Black and colleagues tested 78 samples of dried oregano from shops, the catering trade, and online sellers: 19 (about 24%) were adulterated, typically with 30% to more than 70% of the contents made up of other leaves, most often olive and myrtle, and two contained virtually no oregano. Shop-bought and internet samples fared about the same. Species substitution is built into the trade, since European standards reserve the name for Origanum while the FDA’s spice list applies it to Lippia. Oils vary even more: carvacrol can exceed 80% in Greek oregano oil, sits around 40% in some Spanish oregano oil, and may be minimal in sabinene-type wild oregano from continental Europe. LiverTox notes that oregano oil is not approved as a therapy in the United States, and LactMed points out that dietary supplements do not need proof of safety or effectiveness before sale and that labeled and actual ingredients often differ. Trial results from one product cannot be assumed for another.

Practical points: cooking with fresh or dried oregano needs no special precautions beyond allergy. Concentrated oil deserves the respect of a medicine. Poison Control advises diluting essential oils in a carrier oil before skin use, never applying them to damaged skin, and storing them locked away from children, and essential oils should not be swallowed unless a product is specifically made and labeled for oral use. Anyone choosing a supplement should look for the botanical name and plant part on the label, be wary of products that promise to cure infections, and tell their doctor or pharmacist what they are taking. For marjoram, EMA’s monograph covers teas of the flowering shoots for adults with mild indigestion, and an ointment made by extracting marjoram into petroleum jelly for irritated skin around the nostrils in adults and children over one year.