Oil of Oregano

Paradoxically, the less evidence that exists to support the use of of a treatment, the more passionate its supporters seem to be. I learned this early in my career as a pharmacist. One pharmacy I worked at did a steady business in essential oils. And king of the oils was oil of oregano. Not only were there several different brands of the basic oil, they were different forms, including capsules, creams and even nasal sprays. Not aware of any therapeutic benefits, I would ask customers what they were using it for. I rarely heard the same condition described: skin infections, athlete’s foot, head lice, colds, sore throats, “parasites”, “yeasts”, diabetes, allergies and ringworm were apparently no match against the judicious use of oregano oil. Intrigued, I took a closer look.

Long before our scientific understanding of bacteria and antimicrobials, infected wounds were packed with different products in an attempt to minimize the odour, and hopefully speed healing. It’s likely that someone happened upon a fragrant herb and discovered that it seemed to help treat wounds (or at least, cover some of the smell). Given there have been some amazing drugs with powerful effects that have emerged from natural products, it’s certainly plausible that oil of oregano could have biological and therapeutic effects. Oregano (Origanum vulgare) leaves contain a wide variety of chemical compounds, including leanolic acids, ursolic acids, and phenolic glycosides. Phenolic compounds make up to 71% of the oil. Carvacrol, thymol, cymene, and terpinine and are found in oregano leaves and do appear to have biological effects. It’s these chemicals that are proposed to be the parts with beneficial effects.

The claims made by one manufacturer are unambiguous:

Oreganol P73 is the most powerful germ killer with scientifically proven results against almost every virus, bacteria, parasite, and fungi. The complexity of the phytochemical matrix in Oreganol P73 possesses a broad spectrum of antimicrobial properties that are safe for prolonged use. The oil can be used topically and internally. Oreganol P73 is the medicine chest in a bottle, especially since it is proven never to harm the internal organs, even when used daily for health maintenance.

So if we accept the manufacturer’s claims at face value, there should be evidence demonstrating oregano oil is both safe and effective when used internally and externally. There is apparently also adequate long-term safety data to demonstrate that it can be safely used on a daily basis.


When we contemplate administering a chemical to deliver a medicinal effect, we need to ask the following:

  1. Is it absorbed into the body at all?
  2. Does enough reach the right part of the body to have an effect?
  3. Does it actually work for the condition?
  4. Does it have any hazardous, unwanted effects?
  5. Can it be safely eliminated from the body?

These questions are usually answered through a series of investigations, starting with preclinical (test-tube) studies, and moving into to animal trials, and then to human clinical trials that start with validating safety, and then progress to investigating efficacy and safety.

The short answer is that there’s little beyond animal studies to demonstrate that the ingredients in oregano oil have any effects. One of the best reviews seems to come from the McCormick Science Institute (yes, the spice company).  They commissioned a paper on oregano by Keith Singletary that appeared in the journal Nutrition Today in 2010. Happily, though the journal is paywalled, McCormick is hosting the paper on its own website.

1. Is oil of oregano absorbed? Some parts of the oregano do appear to be absorbed but the bioavailability of its different chemical constituents has not been verified. So we can’t be certain which components are reaching the circulation.

2. Does enough reach the right part of the body to have any beneficial effect? It’s not clear where the chemicals in oil of oregano act in the body, as no research has been done to show that it is adequately absorbed. However, there is some evidence to suggest that oregano may be implicated in inducing abortions in mice, so some parts of the herb must be absorbed, if this a causal effect. When applied to body surfaces or skin for topical effect, oil of oregano is more likely to reach high concentrations, at least locally, and then possibly deliver a medicinal effect. This makes topical effects seem much more plausible than ones that require ingestion.

3. Does it actually work for the condition? There is no published evidence to demonstrate that that oil of oregano is effective for any medical condition or illness. The McCormick review notes that that data for every condition evaluated is “preliminary, inconclusive.”  There is some very limited evidence to suggest that it might be useful for parasite infections — but given the evidence consists of only one study with 14 patients, and no placebo comparison, we really have no idea if the oregano oil itself was effective.

Let’s consider how oil of oregano might treat an infection. Bacteria are killed by antimicrobials based on a specific dose-response relationship. The minimum inhibitory concentration (MIC) must be reached at the site of an infection. Then there’s a concentration range where the bacteria (or viruses, or fungi, or parasites, depending on what you’re treating) are killed, typically in rough proportion to the dose. Keep increasing the dose, and the effect plateaus. If you can hit the MIC without causing side effects or toxicity, congratulations: you have a potential therapeutic agent.

There’s some evidence out there demonstrating that oil of oregano will kill different species of bacteria, etc in the test tube or Petri dish ( in vitro).  If I pour a pile of salt, lime juice, Cointreau, or tequila on a Petri dish, it will likely kill most bacteria too — but that doesn’t mean margaritas can treat pneumonia. It’s not difficult to kill bacteria if you change the conditions enough that it cannot live. So while it’s easy to get high concentrations of oregano in a test tube and subsequent positive effects, these effects are meaningless in the human body unless we can achieve similar concentrations, without any toxicity. And this has not been demonstrated with oil of oregano, or its individual chemical ingredients.

4. Does oil of oregano have any hazardous, unwanted effects? Natural does not mean safe. There are some reports of gastrointestinal upset with oil of oregano. There are also reports of allergic reactions. There is no evidence to suggest that oil of oregano, used at high (medicinal) amounts, may be used safely in pregnant or breast feeding women. However, when used in cooking, and as part of a regular diet, there is also no evidence that causes harm in pregnancy or breastfeeding. Animal studies show that if you give enough carvacrol, it will kill, though.

5. Can oil of oregano be safely eliminated from the body? So little published research exists on oil of oregano there is no way to determine if oregano oil is non-toxic. Certainly, at low doses, when used as a food, there is no reason to have any concerns. But at higher doses, and particularly with regular use, there is no data to sugges it’s safe to consume all that carvacrol, thymol, cymene, and terpinine. As we have no idea if and how oregano oil works, we have no information to estimate what a proper dose might be. Doses published by manufacturers are not based on any published evidence.


Oil of oregano, and the claims attached to it, is a great example of how interesting laboratory findings can be wildly exaggerated to imply meaningful effects in humans. A few small studies have been conducted, mainly in the lab, and advocates argue this is evidence of effectiveness. The rest is all anecdotes.

Despite the hype, there is no persuasive evidence to demonstrate that oil of oregano does anything useful in or on our bodies. And while it is popular, there is no science to support the use of oil of oregano for any medical condition. Suggesting that this herb is can effectively treat serious medical conditions like diabetes, asthma, and cancer is foolish and dangerous. If you’re ill, stick to the proven science, and save your oregano for cooking.

Posted in: Herbs & Supplements

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30 thoughts on “Oil of Oregano

  1. We have many medications that are derived from herbs and are plant based products. One of the oldest plant based products comes from the willow bark which contains acetylsalicylic acid, and is otherwise known as aspirin. Aspirin has been scientifically studied extensively and is a proven medication with known biological activity. Oil of oregano has very few studies to back any of the claims made for it’s use. Untill, we have scientific proof of the efficacy of a substance, we should not recommend it’s use for the treatment of disease. Now that’s science based medicine!

    Dr Sam Girgis

  2. Anthro says:

    I keep trying to tell my wooish acquaintances that if you take some herb, oil, tea, substance in high enough doses to cause a reaction in the body, then it is a DRUG and should be investigated and regulated as such. They only look at me quizically as though they pity me for not seeing the “light”. Sigh.

  3. Epinephrine says:

    One of the oldest plant based products comes from the willow bark which contains acetylsalicylic acid, and is otherwise known as aspirin.

    Willow bark was used as a remedy, but doesn’t contain ASA, it has salicin, which is converted to salicylic acid. ASA is related to this, and can be synthesized from it.

  4. Epinephrine says:

    Posts like this one always make me think of the cectic comic on herbal medicine; I’ll link it in case others haven’t seen it:

  5. Chris says:

    Rats! I’d hope I could convince some enterprising woo-meister into pulling out muchl of the volunteer oregano out of my yard. The stuff self seeds itself all over, and is presently growing into nice two-foot high and round mounds. They could also have all of the California poppies, calendula and lemon balm they like. I did plant the lemon balm like a mint in a contained space, but the stuff spreads through air borne seeds!

    Funny thing about herbs, they are mostly nice smelling weeds. It seems that it would be an easy business to get some ubiquitous smelly plant and tell folks it has certain properties. It would only be slightly less profitable than homeopathy.

  6. Imadgeine says:

    Chris, your yard sounds pretty and must smell good. Your USA weeds are plants we pay lots of money for and lovingly tend in UK.
    Nice post on all natural oregano oil. I ponder a lot on the psychology of this natural = good and science/technology = bad style of thinking. Someone close to me postponed treatment of lymphoma due to this kind of belief. (In case you wonder – I was not kept informed!)
    Polarised thinking is one way in which we simplify all this information overload and deal with the consequent cognitive confusion. The world is just so darn complex. Racial stereotyping is a similar polarising phenomenon. Our lot good, your lot bad.
    There is also a considerable amount of marketing that pushes the natural = good message for all kinds of products. Expensive sea salt crystals are one of my pet examples. Same old sodium chloride, however big the crystals. Same old effect on BP. One producer of natural sea salt is a close neighbour to a nuclear power station but that’s fine isn’t it, as long as the salt came from that all natural sea water.
    Some folk believe this product contains additional beneficial minerals but then so do most foods don’t they?

  7. Chris says:

    Imadgine, I live in a maritime climate that has Mediterranean characteristics (dry summer, mild wet winter, very little freezing), at the same latitude as central France, and within walking distance of this garden. If you travel to Greece, Italy and areas around there you will also see those plants growing in the wild. Rosemary and sage are actual bushes.

    I understand what you mean by the natural “sea salt.” Why is it that sea salt from modern polluted oceans is better than the salt from the mines that were from seas that existed before petroleum products?

  8. daijiyobu says:

    Re: “suggesting that this herb is can effectively treat serious medical conditions like diabetes, asthma, and cancer is foolish and dangerous.”

    If only, here in the U.S., there was some kind of Federal agency that protected consumers from falsely labeled products, especially ones making specific medical claims that simply aren’t true.

    Maybe in my lifetime.


  9. MDJourney says:

    Some more claims by that manufacturer:

    “Another incentive to focusing sales efforts on top-selling branded oregano oil is profit margin. Our product has the highest MRSP of all oregano oils on the market. In fact, it is reassuringly expensive and worth the cost. What does this mean it means that for every bottle you sell, you’ll be making two to three times the profit. More importantly, however, the cost reflects the quality of the product.”


    The truth comes out I guess.

    Also- thank you for this article. I always find your contributions to SBM straightforward and well researched.

  10. desta says:

    @ Chris: I have weedy oregano plants taking over the yard, too, but my area gets long cold winters and is not much like the climate of France, sadly. The oregano has never been watered or tended, but it gets bigger and bigger every year. Big cash cow of woo! ;)

    Right now it’s perfect for cooking and I’ve no time to pick it, but later in the summer, after it blooms, I notice the flavor becomes rather bitter. Maybe those are the precious oils I could market to woo lovers? If it’s bitter, it must cure something, right?

  11. TsuDhoNimh says:

    Most of the strongly aromatic herbs – oregano, thyme, rosemary, salvias – and anything with a lot of terpinoids – pine needles, juniper berries – can be boiled into a tea to make useful antiseptic wound washe if you are out of range of real medicine.

    The modern woo-meisters have vaguely heard of Native American practices that were practical and bestowed magical cure-all properties on them.

    My absolute favorite borrowing is an herb “said to have been used by the elders of the Pueblo tribes for centuries to improve their vitality” … it’s still in use, and it’s a laxative herb.

  12. Margaritas do prevent pneumonia. Whenever I have gone out with friends for margaritas, (is today friday?), none of them has had pneumonia, and I cannot remember any of them coming down with pneumonia for the additional day that those few margaritas might be having their physiologically obvious extended benefit.

  13. Chris says:

    Margaritas are made with tequila, which is made from a certain kind of agave. And agave nectar is supposed to be good for you, so it is obvious that margaritas prevent pneumonia. ;-)

    (too bad I dislike tequila, I’ll stick to gin which is made with juniper berries and I can mix it with quinine)

  14. Interesting article Scott Gavura. I like to see the thought process behind analyzing the possible benefits of a substance.

    I have an “all-natural” hand sanitizer spray that contains oregano oil (pretty low on the ingredient list, also aloe and various other things that I can’t read because the type is too tiny).

    I bought it from a sample bin on a whim because it’s alcohol free purse sized and smells nice, like oregano. My hands crack in winter, so the alcohol hand sanitizers can sting like crazy. I wonder if oregano oil actually works as a hand sanitizer, if it’s one of the other ingredients that works or if the product doesn’t work at all. Who knows.

    I wonder if oregano would be good in a margarita, or to replace the mint in a mojito.

    @Chris – I hate (hate, hate) lemonbalm, spreads like crazy even in Michigan. My oregano is quite well behaved though. We need pictures of your garden.

  15. Chris says:

    I wonder if oregano would be good in a margarita, or to replace the mint in a mojito.

    Absolutely not for a mojito (I dislike margaritas because of the tequila). It really does not taste the same. Though I have taste receptors so sensitive to aldehydes that cilantro tastes like soap (see this NY Times article on cilantro haters), so I use oregano in Mexican style dishes. And I have made a really nice pesto using oregano, parsley and walnuts for pasta.

    Have you ever tried growing thimble berry? I got some just because my dad raved about eating it as a kid growing in central Washington, but it spreads like crazy. So I pulled it up. I have found a patch of it growing a couple of miles a way, so I know where to grab a bit once in a while.

    Here are some of my alliums with oregano mounds under them. There are some more pictures in that album, I think I will add some more pictures it. I just planted a teeny tiny pink popcorn patch in about a six square foot space.

  16. Calli Arcale says:

    Regarding sea salt, there is actually a difference (well, several differences, actually) between sea salt and mined salt. As to which is better . . . well, that depends.

    In terms of cuisine, the shape and size of the salt is more important than its origin. Usually; rock salt or sea salt may have more flavor to it than purified table salt, but honestly, the sheer saltiness of it will probably overwhelm that. The shape’s more important. Which shape is best depends on the job you want it to do. Different shapes have different surface areas, after all.

    As far as health, the biggest difference between sea salt and most rock salt (and all purified salt) is that sea salt is not all sodium chloride plus impurities. It’s actually two salts: sodium chloride and potassium chloride. Potassium chloride isn’t a problem for people on a sodium restriction, so sea salt may be slightly healthier (or, more accurately, less unhealthy). But honestly, it’s a bit like touting that your deep-fried cheese curds are fried using non-trans-fat oil — nice, but it’s kind of ignoring the main problem.

  17. Chris says:

    Not all mined salt is purified. Some you can get in the actual pink to red color. The vaulted Himalayan Pink Salt is mined (and the color comes from the halophilic bacteria). If you ever travel to the area near Salzburg, Austria go on a salt mine tour, not only are they fun but you can see the salt as it was (the name of the city sounding like “salt” is not a coincidence).

  18. Calli Arcale says:

    Agreed; I didn’t mean to imply all mined salt is purified. I meant that in general, the stuff you get at the supermarket (unless you specifically go for something else) is likely to be purified mined salt. (With iodine added to prevent goiter, of course.)

    I’ve always wanted to visit one of those salt mines; in some, the miners carved elaborate and beautiful chambers out. Evidently, their job got a little tedious at times. ;-)

    I have a jar of “Jurassic Sea Salt”. It’s rock salt from a mine in Utah (IIRC). The salt deposit dates to the Jurassic period, where it was laid down as an inland sea evaporated. It’s a lovely shade of pink, and the fact that different chunks are subtly different colors sort of adds to the fun. My seven-year-old daughter thinks it’s just amazingly cool because she can imagine pleisiosaurs swimming in that inland sea. ;-)

  19. MDElen says:

    The healing powers of oil of oregano were virtually unknown in North America until the early 190Os, even though our ancestors have relied on its medicinal effects for thousands of years. Hippocrates wrote volumes on how to use this medicinal herb in the treatment of many conditions. In recent years, oil of oregano has been largely investigated for its antimicrobial properties.

  20. hojo70 says:

    The first point I would like to make is that the lack of modern formal clinical studies doesn’t prove inefficacy. Although the oil itself as a complete product has not been clinically studied, the active chemical compounds that make up the oil have. Oregano has been used since Greek and Roman times and was widely regarded as the main herb in the health and medicinal fraternity – and even before the Greeks discovered the benefits of oregano, it is recorded that it was being used by the Assyrians in 3000BC. Aristotle had been known to both write about and use the plant oils himself. A Google search turns up hundreds, possibly thousands, of references of random persons who have benefited from the medicinal qualities of the ingredients contained in the oil. You want a “reliable” study? How about one that has lasted over 5000+ years with potentially hundreds of thousands of humans whom have benefited.

    1. Scott Gavura says:


      Although the oil itself as a complete product has not been clinically studied, the active chemical compounds that make up the oil have.

      Please list the citations of clinical trials with relevant endpoints in human subjects with any of the major chemical constituents. I’m ready to revise my post if you produce them.

  21. WilliamLawrenceUtridge says:

    hojo70, if oregano is truly effective, it should be trivial to prove it in controlled studies. Something being old doesn’t make it effective. Bloodletting is old, that doesn’t make it effective. A “reliable” study is not determined by longevity, but rather by scientific controls. Don’t worry, if oil of oregano is truly effective, the results will be positive irrespective the limitations placed by high quality science.

    Anyone can claim anything is effective at curing any disease. An ethical approach would be to test it rather than merely asserting it.

  22. Harriet Hall says:


    You have committed at least four logical fallacies: post hoc ergo propter hoc, the argument from popularity, the argument from authority (Aristotle, no less!), and the “ancient wisdom” fallacy. You cite anecdotes, not studies. The kind of “evidence” you cite is equivalent to the “evidence” for bloodletting, which is just as ancient and probably “benefited” far more people than oregano over the centuries. Despite all those who believed it worked, it actually did more harm than good. Only good science can tell us whether oregano really works.

  23. libby says:

    @Dr Sam Girgis

    You state: “Untill, we have scientific proof of the efficacy of a substance (oregano), we should not recommend it’s use for the treatment of disease.”

    Why would anyone test something you can grow in your back yard? Who would anyone put up money towards a substance that will not generate exclusive financial gain?

    When a health system is placed in the hands of a free market system, only those substances that are patentable and potentially profitable will be tested. This self-limitation is hardly adequate to determine the benefits of ALL substances.

  24. Chris says:


    Who would anyone put up money towards a substance that will not generate exclusive financial gain?

    Read the thread a bit more. We were speculating that since it is so abundant that folks were trying to make money while getting rid of it.

    Yesterday I just cut back several bunches of it yesterday, and if I have time I’ll be digging out more that are taking over some garden areas. It would be great if I could convince someone it was a cure for something and sell the stuff instead of having it turn to compost!

  25. Harriet Hall says:


    “Why would anyone test something you can grow in your back yard?”

    Because they wanted to know if it worked?
    Also, because if they could isolate a useful active ingredient or develop a unique preparation they could patent a product and make money.

  26. WilliamLawrenceUtridge says:

    My mother buys both powdered oregano leaf and oil of oregano capsules despite growing oregano in her garden. Any visit to a health food store will demonstrate choices for oregano pills, both in oil and powdered form. There is obviously a market for herbal products, catering to people willing to shell out money for untested substances. Why would anyone test something that you can grow in your backyard? Because there’s a market and the market would grow markedly if there were evidence behind it. Herbal companies are gambling that their products work enough to convince people but aren’t confident enough to actually test them. That makes Big Herbal less ethical than Big Pharma in my mind, the only thing saving their asses is the fact that their products don’t seem to have dramatic enough side effects to cause serious harm.

  27. libby says:


    You state: “….if they could isolate a useful active ingredient or develop a unique preparation they could patent a product and make money.”

    But if that were the case, some creative thinker might say to herself, why don’t I just eat a whole lot of oregano that contains this ingredient. It is that scenario that makes drug companies the most nervous, self-administration of a chemical easily attainable.

  28. WilliamLawrenceUtridge says:

    But if that were the case, some creative thinker might say to herself, why don’t I just eat a whole lot of oregano that contains this ingredient. It is that scenario that makes drug companies the most nervous, self-administration of a chemical easily attainable.

    Ever wonder why people take aspirin instead of chewing willow bark? It’s more convenient, it’s purified, you get a consistent dose, it has been modified to be easier on the stomach, and it’s more effective. Plants did not evolve to meet our needs, bar those that humans have selectively bred to become less toxic, have larger fruits and taste better.

    All of the natural products that exist now existed in the past. And just like the past, they are less effective than the refined, purified, and chemically modified substances produced by pharmaceutical manufacturers. There’s a reason why people live longer now than they did in the past – medicines from the past were less effective.

    And again, if these medications are soooooo effective, it should be easy to demonstrate this in scientifically controlled tests. But someone will still need to plant, cultivate, harvest, process and package the products, and that will be a large company just like the “Big Pharma” people demonize. The difference of course, is the level of scrutiny required on the substance, the safety margins, the batch-to-batch consistency testing and of course, the effectiveness testing that is missing from herbal products. Nature doesn’t love us, and doesn’t make a habit of producing plants that are inherently good for us. It’s always a bargain, and science can always make the products better, purer, cheaper, more effective and safer. Plucking something out of your garden as a form of medicine a) probably won’t work and b) exposes you to unknown dangers.

  29. Chris says:

    WLU, once upon a long time ago on Usenet someone posted where he/she could buy good herbs on the newsgroup. I responded with a link to the herb section of a seed catalog telling him/her to grow his own.

    libby, which do you think is safer: taking digitalis for certain heart conditions, or making up a pot of foxglove tea?

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