Oregano

Scientific Name(s): Origanum onites L., Origanum syriacum L., Origanum vulgare L.
Common Name(s): Kekik, Mediterranean oregano, Mexican oregano, Mountain mint, Wild marjoram, Winter marjoram, Wintersweet

Medically reviewed by Drugs.com. Last updated on Jul 9, 2024.

Clinical Overview

Use

Aside from its culinary application, oregano exhibits antimicrobial and antioxidant actions and has possible activity as an antispasmodic and in diabetes. However, there is limited clinical trial evidence to support the use of oregano for any indication.

Dosing

There is no clinical evidence to support specific therapeutic doses of oregano; however, due to its wide use in foods, it has been designated GRAS (generally recognized as safe) status by the FDA. In a small study, 200 mg/day emulsified O. vulgare oil was administered for 6 weeks.

Contraindications

Contraindications have not been identified.

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking. GRAS status when used as food. Ingestion in excess of amounts found in food should be avoided because safety and efficacy are unproven. Some studies indicate hormonal effects.

Interactions

None well documented.

Adverse Reactions

Oregano has caused allergic contact dermatitis when applied topically. When oregano is ingested, eczematous rash and, rarely, anaphylactic reactions can occur.

Toxicology

Information in humans is lacking.

Scientific Family

• Lamiaceae (mint)

Botany

Common or wild oregano is a perennial plant native to the Mediterranean region and Asia and cultivated in the United States. Its creeping rootstock produces a square, downy, purplish stem with opposite ovate leaves. Stems can grow up to 76 cm tall and are dotted with small depressions. Purple, 2-lipped flowers grow in terminal clusters from July to October.(1, 2, 3)

O. vulgare subspecies hirtum has a spicy flavor, furry leaves on stems that grow up to 45.7 cm tall, and floppy white flowers.(1) Several Turkish species of Origanum are also found in commerce, including O. onites L. and O. syriacum L.(4) Other taxa in the genera Coridothymus, Thymbra, and Satureja have similar chemistry.(4) Lippia graveolens Kunth. (Verbenaceae) is known as Mexican oregano.

Molecular techniques to distinguish these related species for purposes of quality control have been developed.(5, 6, 7, 8)

History

Oregano has been a common ingredient in Spanish, Mexican, and Italian dishes as a spice and flavoring agent for hundreds of years. Its initial purpose was as a warming digestive and circulatory stimulant. It has been used in perfumery for its volatile oil contents, especially in scenting soaps.

The antiseptic qualities of aromatic and medicinal plants and their extracts, including oregano, have been recognized since ancient times.9 Attempts to characterize these properties in the laboratory date back to the early 1900s.

Antispasmodic, calmative, carminative, diaphoretic, expectorant, stomachic, and tonic actions have been reported. It has been suggested that an infusion of the fresh herb is beneficial in treating an upset stomach and indigestion, headache, colic, and nervous complaints, as well as for coughs and other respiratory ailments. An infusion of the flowers has been used to prevent seasickness. The oil has been used externally in liniments and lotions and to ease toothache. It has also been used as an ant repellent.10, 11, 12

Chemistry

The monoterpenoid phenols carvacrol and thymol are responsible for many of the properties of the essential oil, as well as p-cymene and terpinene.2, 13, 14, 15, 16, 17, 18 Of the numerous species considered as oregano, all have carvacrol as the major component of their essential oils.4 Phenolic compounds may represent more than 70% of the total oil. Biosynthetic pathways of O. vulgare, which produce monoterpenoids, have been elucidated in the glandular hairs of the plant.19, 20 The essential oil may play a role in deterring herbivores, such as snails, from feeding on the plant.21

Analytical methods for determining the constituents of oregano oil include thermal desorption gas chromatography-mass spectral and liquid chromatographic-mass spectral methods.22, 23 Using gas chromatography, 4 chemotypes of Italian O. vulgare were identified in the wild.24 Infrared and Raman spectroscopy have been used to distinguish chemotypes as well.25 In addition to classical steam distillation, supercritical fluid extraction with carbon dioxide has been studied.26, 27 The effect of drying methods on essential oil content has been defined.28

Oregano also contains oleanolic and ursolic acids; flavonoids29 and hydroquinones; caffeic, rosmarinic, and lithospermic acids; tannins; and phenolic glycosides.30, 31, 32, 33

The metabolism and pharmacokinetics of oregano phenolics have been defined in rats34 and humans.35

Uses and Pharmacology

Some of oregano's pharmacologic actions may be connected to activation of the transient receptor potential (TRP) channel V3, which mediates warm sensations, by carvacrol and thymol.(36) In addition, carvacrol and thymol rapidly activate and desensitize TRPA1, another similar receptor.(36) These are distinct from the action of capsaicin, the pungent principle of chili pepper, which activates TRPV1, and menthol, the cooling principle of mint, which activates TRPM8. There are few clinical studies on the medicinal effects of oregano, despite its widespread culinary use.

Analgesic effects

Clinical data

Possible oral analgesic applications of carvacrol were supported by data in a human experiment (n=25) that documented the desensitizing properties of carvacrol to oral irritation and innocuous heat application.(96)

Antibacterial activity

The volatile oil of oregano has demonstrated in vitro antibacterial activity against a wide range of gram-positive and gram-negative microorganisms, including Listeria, Pseudomonas, Proteus, Salmonella, and Clostridium species(11, 15, 16, 53, 54, 55, 56, 57, 58, 59) as well as some methicillin-resistant Staphylococci.(15, 60) An ointment formulation targeting methicillin-resistant Staphylococcus aureus (MRSA) has been developed.(61) Low to moderate activity against Helicobacter pylori has been demonstrated.(62, 63, 64) Oregano oil appears to inhibit organisms at relatively low concentrations(65) and its activity is primarily due to the phenolic components thymol and carvacrol.(15, 60) Functional changes in bacterial cell membrane potential and permeability have been linked to oregano oil treatment.(66) The effect of oregano oil on foodborne bacterial pathogens has been widely studied.(16, 38, 56, 57, 58, 59) Some methods of essential oil extraction appear to yield oil with poor antibacterial properties.(67)

Antifungal activity

Oregano inhibited aflatoxin production and prevented growth of Aspergillus at concentrations as low as 0.1%.(47, 48, 49) Further studies have compared the effects of oregano essential oil, thymol, and carvacrol, which all completely inhibited fungal growth of Aspergillus and Penicillium species.(50) Oregano oil has exhibited some antifungal activity against Candida species, possibly because of its carvacrol content.(14, 18, 51) Synergism of oregano oil antifungal effects with nystatin has been observed in vitro.(52)

Antiinflammatory effects

A supercritical fluid extract of O. vulgare reduced proinflammatory cytokines, while increasing antiinflammatory interleukin (IL)-10.(27) Rosmarinic acid, oleanolic acid, and ursolic acid were identified as the antiinflammatory constituents.(23) A combination of thyme and oregano oils were found to reduce the expression of proinflammatory cytokines in a mouse model of colitis. Protein levels of IL-1beta and IL-6 were also reduced.(75)

Antioxidant activity

Many experiments have demonstrated that in vitro antioxidant activity of oregano essential oil and its constituent compounds rosmarinic acid, carvacrol, and thymol are similar to or better than alpha tocopherol.(3, 15, 37, 38, 39, 40) Accelerated solvent extraction was proposed to yield higher antioxidant activity than room temperature extraction.(41) Vanillin, vanillic acid, and protocatechuic acid from O. vulgare showed both antioxidant activity and inhibition of cellular melanogenesis(42, 43) while a novel phenolic glycoside from oregano also inhibited melanogenesis.(44) Long-term dietary administration of oregano to rats reduced carbon tetrachloride-induced oxidative stress.(45) The clinical importance of these effects is not yet established. In a double-blind, placebo-controlled trial among healthy adult men, no differences in biomarkers of lipid peroxidation were found with oregano extract supplementation.(46)

Antiparasitic action

In 1 study, 14 patients with known parasites were administered 200 mg emulsified O. vulgare oil for 6 weeks. Entamoeba hartmanni, Endolimax nana, and Blastocystis hominis were eradicated from 13 patients.(68) Several oils, including oregano, were shown to inhibit Giardia trophozoite growth and viability.(69) The oil of O. vulgare has been shown to eradicate common parasites in chickens and pheasants. In vitro experiments showed activity against Trypanosoma cruzi.(68, 70)

Antispasmodic effects

Origanum compactum has been used in Morocco as a spasmolytic, prepared as a tea from flowers and leaves of the plant. The rapid spasmolytic action of O. compactum was demonstrated in in vitro experiments after using acetylcholine on smooth muscle preparations to produce contractions. It is suspected that the herb stabilizes the muscle membrane by interfering with the influx of calcium and its regulatory proteins.(2) The active components in the O. compactum essential oil appear to be thymol and carvacrol.(71)

Cancer

Essential oils of O. syriacum and O. vulgare inhibited growth of breast cancer cells in vitro; however, they were not cytotoxic.(79) Oregano ethanolic extract induced apoptosis in human colon cancer cells.(80) In rats, whole oregano given orally markedly inhibited dimethylhydrazine-induced colon cancer at 40 mg/kg.(81) Galangin and quercetin from oregano were shown to be antimutagenic in an Ames test with Salmonella typhimurium TA98.(82) Thymol had genotoxic activity in a Drosophila model; however, this activity was antagonized by carvacrol.(83)

Diabetes

Researchers have demonstrated a hypoglycemic effect of oregano in rats with induced diabetes, providing some supportive evidence for the use of oregano leaves in diabetic patients. The effect was independent of insulin and occurred after a single dose, as well as with repeated daily dosing.(72)

Other researchers have demonstrated an aldose reductase inhibitory effect by lithospermic and rosmarinic acid extracted from oregano. Some researchers have suggested that inhibiting the accumulation of sorbitol may contribute to the prevention of chronic complications, such as retinopathy and peripheral neuropathy in diabetic patients.(13, 73)

Another group reported constituents with both antagonistic and agonist effects at the peroxisome proliferator-activated receptor gamma, which could be of use in metabolic syndrome.(74)

Hyperlipidemia

Both oregano essential oil and aqueous infusions showed inhibitory activity against low-density lipoprotein (LDL) oxidation, with different constituents responsible for the activity in the 2 preparations.(76) In hyperlipidemic patients, 25 mL of an aqueous distillate of O. onites (oregano water) taken daily enhanced the effects of altered lifestyle and low-fat diet interventions in modulating mild hyperlipidemia.(77)

Oral analgesic

Possible oral analgesic applications of carvacrol were supported by data in a human experiment (n=25) that documented the desensitizing properties of carvacrol to oral irritation and innocuous heat application.(93)

Wound healing

The effect of 3% oregano ointment (free of potentially irritating essential oils) on wound healing was investigated in a small double-blind, randomized, controlled trial (n=40) conducted in adults undergoing dermatological excisions. Oregano in petrolatum or petrolatum only was applied twice daily for a mean of 12 days. Although 1 patient (6%) in the oregano group and none in control tested positive for MRSA, fewer patients in the oregano group tested positive for S. aureus (19%) or were treated for cellulitis (6%) compared to controls (41% and 16%, respectively). Additionally, both patient- and physician-scored scar assessments were significantly better in the oregano group compared to controls. No significant adverse reactions were noted in either group.(94)

Other

Monoamine reuptake inhibition in the rat brain by an oregano extract was observed, and serotonin levels, as measured by microdialysis, were elevated by the same extract.(78)

Dosing

There is no clinical evidence to support specific therapeutic doses of oregano. Due to its wide use in foods, it has been designated GRAS by the FDA.84 A study evaluating the antiparasitic effect of oregano used 200 mg emulsified O. vulgare oil daily for 6 weeks.68

Pregnancy / Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking. GRAS status when used as food.

A retrospective review of poison center data in Uruguay from 1986 to 1999 analyzed an over-the-counter herbal preparation (Carachipita) containing oregano and other herbs commonly used to induce abortion. GI symptoms, genital hemorrhage, and multiple organ system failure, resulting in 4 abortions, occurred in 13 women who received this preparation.85 Dried oregano herb (1 g) contains approximately 4 mcg of phytoprogestins, which bind to progestin-binding sites.86

In a study of natural herbs as alternatives to antimicrobials, a decrease in sow and litter mortality occurred in an experiment in which sows were fed oregano leaf, flower, and essential oil-enriched food. No apparent ill effect was reported.87 Another study found that mice fed oregano essential oil showed an increase in the proportion of dead cells in preimplantation embryos.88

Interactions

None well documented.

Progestins: Herbs (progestogenic properties) may enhance the adverse/toxic effect of progestins. Monitor therapy.Zava 1998

Adverse Reactions

Allergic contact dermatitis caused by spices, including oregano, is well documented.88 Although oregano is frequently consumed, there are a few reports of adverse or systemic reactions. One report of anaphylaxis exists, and cross-sensitivity with other members of the Lamiaceae family has been noted.89 An additional case report of an eczematous reaction to ingestion of large quantities of oregano has been published.90

Data collected between 2004 and 2013 from 8 US centers in the Drug-induced Liver Injury Network revealed that 15.5% (130) of hepatotoxicity cases were caused by herbals and dietary supplements, whereas 85% (709) of cases were related to prescription medications. Of the 130 cases of liver injury related to supplements, 65% were from non-bodybuilding supplements and occurred most often in Hispanics/Latinos compared with non-Hispanic whites and non-Hispanic blacks. Liver transplant was also more frequent with toxicity from non-bodybuilding supplements (13%) than with conventional medications (3%) (P<0.001). Overall, the proportion of severe liver injury cases was significantly higher for supplements than for conventional medications (P=0.02). Of the 217 supplement products implicated in liver injury, 175 had identifiable ingredients, of which oregano was among the 32 (18%) single-ingredient products.92

Related/similar drugs

Toxicology

In a study investigating the effect of oregano on growth and development of mouse embryos, an increase in the proportion of dead cells in preimplantation embryos was observed.88 The isolation of toxic aristolochic acids from Russian O. vulgare has been reported in one investigation.91

Index Terms

• Coridothymus
• Lippia graveolens Kunth.
• Satureja
• Thymbra
• Mexican oregano

References

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