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Oregano benefits and side effects

Oregano (Origanum vulgare) is a popular culinary spice used in the Mediterranean diet that is also known for its high antioxidant content.

It has traditionally been used to treat gastrointestinal issues and to alleviate pain and inflammation associated with rheumatism, toothache and earache.

Early studies show it may help fight bacteria, reduce the growth of cancer cells and play a role in lowering cholesterol.

The active components appear to be phenolic structures, such as carvacrol and thymol, and triterpenoids, such as ursolic acid. Both dried oregano leaves and fresh essential oil provide various benefits.

Most of the available research has been limited to in vitro and in vivo animal studies. Researchers are interested in further studying oregano’s effects in humans.


Oregano is rich in antioxidants. Free radicals have long been associated with the development of various diseases and conditions, including cancer, atherosclerosis, Alzheimer’s disease and Parkinson’s disease. Free radicals are unstable molecules that can form a domino-like effect to damage cells.

The best defenses against the accumulation of these free radicals are antioxidants. Several in vitro studies show oregano’s high antioxidant content (1).

In one study, carvacrol and thymol were identified as the main antioxidant components of oregano oil. Researchers noted that the antioxidant activity of the oil increased as the concentration of the oil increased (2).

Oregano may protect and treat a range of bacteria. In a study evaluating the chemical composition and biological activity of a crop of pink flowered oregano, researchers found that the essential oils showed antimicrobial activity against gram-positive pathogens, particularly Bacillus cereus and B. subtilis — two strains of bacteria that cause food poisoning (3).

Oregano has also been shown to be efficacious against 23 different species of bacteria, thanks to carvacrol and thymol compounds.  (4).

Current research is limited to in-vitro studies that have used concentrated amounts of oregano. Further research is needed to determine how these results could affect humans.

Oregano may also help treat viral infections. Carvacrol and thymol are the two compounds that have once again been identified as being beneficial, this time, in fighting viruses.

According to a 2014 issue of the Journal of Applied Microbiology, carvacrol is effective in inactivating nonenveloped murine norovirus (a species of norovirus affecting mice) within one hour of exposure (5).

Researchers are hopeful that with further studies, oregano and its component carvacrol may prove to be an effective sanitizer to control human norovirus. Norovirus is a highly contagious gastrointestinal virus that causes vomiting and diarrhea.

In another study, thymol and carvacrol both possessed significant antiviral activity, and they were capable of killing 90 percent of herpes simplex virus type I within one hour (6).

Oregano has pain-relieving capabilities. The aim of a recent study, published in the Iranian Journal of Pharmaceutical Research, was to evaluate the pain-relieving effect of aqueous extract of oregano in a rat model of acute pain test. Sixty-three rats were used in the study.

The results of the study suggest that aqueous extract possesses antinociceptive activity — the ability to reduce sensitivity to painful stimuli — in a dose-dependent manner (7). Specifically, injection of oregano extract resulted in a significant increase in the response latency during the Tail-Flick test.

Oregano may help lower cholesterol. According to the results of a study published in the International Journal of Food Sciences and Nutrition, essential oils and aqueous tea infusions of oregano provide a protective effect against LDL oxidation (8). Oxidized LDL levels put people at increased risk for metabolic syndrome, cardiovascular disease and heart attack.

The results were a part of an in vitro study; the effect on LDL oxidation following oral supplementation in humans is not yet known.

Oregano may help treat diabetes. Due to oregano’s antioxidant and anti-inflammatory activity, researchers believe it may be a future diabetic treatment. When comparing the efficacy of methanolic oregano extract versus aqueous oregano extract in a mouse study, methanolic extract proved to be far more efficacious in protecting mice from diabetes development.

Rosmarinic acid, a compound in methanolic oregano extract, exhibited partial protection from diabetes; researchers believe there are other compounds in methanolic oregano extract responsible for its beneficial effects (9).

In another study, treatment of mice with ethyl acetate extract of oregano protected them from the development of hyperglycemia (an excess of glucose in the bloodstream) 10.

Oregano may have an anti-cancer effect. Early in vitro studies show this spice’s potential to kill cancer cells. Using a human colon cancer cell line, researchers found that ethanolic extract of oregano leads to cell death in a dose- and time-dependent manner (11).

In another study, carvacrol was shown to inhibit the growth and spread of the two colon cancer cell lines used in the study, in a concentration-dependent manner.

Early results suggest that carvacrol may have therapeutic potential for the prevention and treatment of colon cancer (12).

Side effects

Unlike the herb used to flavor food, commercially-prepared oregano oil is highly concentrated. When taken long-term or in high doses, it may cause several adverse effects, including gastrointestinal issues such as nausea and vomiting and hyperactivity. These side effects may be due to thymol, one of the phenols found in oregano.

Oregano may also cause an allergic skin reaction, especially in those who are allergic to other plants in the oregano family, such as mint, sage, basil and lavender.

Topical application may cause a skin irritation or sensitivity even in those who are not allergic to oregano or other plants from the same family.

There is also concern that oregano supplementation may increase the risk of bleeding and interfere with diabetes medication.

Recommended dosage

Studies are lacking on the recommended doses of oregano supplementation in humans. Commercially-sold supplements have recommended doses, established by their manufacturers. Carefully follow the dosage guidelines and do not take long-term until further studies are performed.


In addition to being a popular Mediterranean spice, oregano supplementation may effectively treat a range of conditions. It is being studied for its ability to treat bacterial and viral infections, diabetes, certain cancers and high cholesterol.

It has also been shown to have antioxidant and anti-inflammatory properties and may help alleviate pain.

Both dried oregano leaves and fresh essential oil provide various benefits.

Research has been mostly limited to in-vitro and animal studies; further research is needed to determine how supplementation could affect humans.


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Author: laura