Oil of Oregano is a potent antiseptic used both topically and internally. Research demonstrates that it is effective in killing a range of organisms, especially yeast and bacteria. The body of positive evidence for oregano oil as a major antibiotic is growing. Among 52 plant oils tested, oregano was considered to have "pharmacologic" action against common bugs such as Candida albicans (yeast), E. coli, Salmonella enterica and Pseudomonas aeruginosa. [Journal Applied Microbiology, Volume 86, June 1999] Pseudomonas is a type of germ that is getting more difficult to treat as it has developed strains that are resistant against antibiotic drugs.

• Oil of oregano at relatively low doses was found to be efficacious against Staphylococcus bacteria and was comparable in its germ-killing properties to antibiotic drugs such as streptomycin, penicillin and vancomycin. [Science Daily 10/11/2001]
• Researchers at the Department of Food Science at the University of Tennessee reported that, among various plant oils, oil of oregano exhibited the greatest antibacterial action against common pathogenic germs such as Staph, E. coli and Listeria. [Journal Food Protection, Volume 64, July 2001]
• British researchers reported oregano oil had antibacterial activity against 25 different bacteria. [Journal Applied Microbiology, Volume 88, February 2000]
• Of recent interest are reports showing that carvacrol from oil of oregano kills spores, such as Bacillus cereus and Bacillus anthracis (anthrax). [Archives Microbiology, Volume 174, October 2000; Quarterly Review Biology, Volume 73, March 1998] Bacillus cereus is considered to be from the same species as Bacillus anthracis (anthrax).
  [Applied Environmental Microbiology, Volume 66, June 2000] In tests of antibiotics and antiseptics, Bacillus cereus is often used in studies in lieu of the anthrax strain. [University of Michigan News & Information Service, Sept. 23, 1998]
• The growing problem of antibiotic resistance has health authorities concerned. Already various germs are showing resistance to vancomycin, particularly to intestinal bacteria (Enterococcal species) among hospitalized patients. [Southern Medical Journal, Volume 94, August 2001]
• Vancomycin is considered to be the most potent antibiotic available and is withheld from use as a drug of last resort. Drug resistance does not develop against naturally-occurring antibiotics such as garlic and oil of oregano.
While the killing action of oregano oil in many studies was the result of activity in a "test tube" or culture media, enterically coated products will deliver the oil into the GI tract. These antibacterial actions have not yet been confirmed by human clinical trials.

Oil of oregano is not to be confused with common oregano in the kitchen spice cupboard, which is usually Oregano marjoram rather than true oregano (Oregano vulgare).

The essential oil distilled from oregano leaves contains varying amounts of thymol and carvacrol which can constitute as much as 90% of the oil. One should be sure to get oregano oil from a reputable company, for it has been suggested that many of the oils available commercially are derived from non-oregano species, particularly various types of marjoram and thyme. Furthermore, there are different concentrations of oregano oil available that are being made with different extraction processes which may involve the use of solvents. Typical doses, depending on the concentration are 1-4 drops, capsules or tablets; 1-4 times per day.

You can try adding bulk oregano oil to capsules when taking it internally. Start with a small amount and increase slowly. It is best when taken with food. However, since this volatile oil is quickly absorbed and associated with inducing heartburn, some may require them to be taken in coated capsules, so they do not break down in the stomach but instead are delivered to the small and large intestine. This also delivers the oil further down in the GI tract, where its killing action may be needed.

When using pure oregano oil topically, make sure to dilute it in a carrier oil such as almond, olive, or another pure vegetable oil to avoid burning the skin. Avoid canola oil and Wesson or other commercial vegetable oils.

Caution
Oil of oregano may reduce the absorption of iron, so take the oil at least two hours before or after consuming iron supplements. Side-effects are minimal, but allergic reactions to oregano oil and a sensitivity to plants in the same family (thyme, basil, hyssop, marjoram, mint, sage) can occur. It should not be applied in full strength to the skin.