How Ayurveda Works (Not Really)

This piece appeared in The Hindu this morning – Understanding How Ayurveda Works. The Hindu does have a soft corner for “complementary and alternative medicine” (CAM), but normally it’s limited to the writings of B.M. Hegde in the “open page”, where anyone can write in. This is different – it appeared in the Science and Technology section.

The piece starts with a list of differences between what it calls “traditional medicine (TM)” and “modern medicine (MM)”. Including this: “TM looks at results, not how the treatment works while MM advances by understanding the mechanism of action, and cause and effect.” This is a convenient trope in CAM – convenient because it absolves CAM proponents from explaining how their drugs do what they’re claimed to do. The rest of the article describes a study done on 2 ayurvedic preparations which was published about two years ago in PLOS ONE – “In Vivo Effects Of Traditional Ayurvedic Formulations in Drosophila melanogaster Model Relate with Therapeutic Applications”.

The scientists did an experiment on the effects of these formulations on fruit flies – one formulation is based on amla (gooseberry), the other contains mercury sulphide. As if often the case with CAM substances, their supposed benefits are multitudinous – one “enhances life expectancy, body strength, intellect, fertility and gives freedom from illness”, and the other is used “in a wide variety of disorders including chronic and recurrent infections (pneumonia/bronchitis), fistula-in ano, rheumatological diseases especially those of auto-immune origin, sexual and general debility and benign and malignant neoplasms”. With an aim of analysing “effects of the whole Ayurvedic formulations rather than their “active” components”, the scientists tested the fruit flies for “effects on longevity, development, fecundity, stress-tolerance, and heterogeneous nuclear ribonucleoprotein (hnRNP) levels”.

The problem is plausibility – no plausible mechanism for these substances to have these effects is given, other than a routine mention of anti-oxidants. Science-based medicine looks at plausibility because the prior probability of a drug working makes a big difference to such studies. This article – The Plausibility Problem – explains pretty much everything you need to know on the subject, including things like true/false positives/negatives, what we mean by power and specificity of a study, prior probability and positive predictive value. (Also see this other article on science-based vs. evidence-based medicine.) This is essentially Bayesian reasoning. In a nutshell, a low prior probability matters:

Even for a well designed, powerful study, if the premise is highly unlikely, a positive result does not give us convincing evidence that the premise is true. For studies with weaker power, the results are even less persuasive. So why do extraordinary claims require extraordinary evidence? Because for implausible claims, ordinary evidence is highly unreliable. A single positive study with a P value of .05 is ordinary evidence. For a very implausible hypothesis, a result of this sort is quite likely to be a false positive.

So without any hypothesis on how amla and mercury sulphide have these beneficial effects on “life-history”, this single study cannot be taken as proof that they have these effects. The vagueness of the supposed benefits is problematic too (and is a common trope in CAM with its descriptors like “holistic”, “boosts immunity”, “removes toxins”, “promotes well-being”). The more specific the claimed benefit, the easier it is to test it. (Compare the ayurvedic vagueness with the highly specific benefits and mechanisms of gooseberry listed here.)

Here’s a contrasting example also from “ancient” medicine – the anti-malarial drug Artemisinin. Artemisinin comes from the herb Artemisia annua, and its anti-malarial properties were first described by Tu Youyou and colleagues in the 1960s when Chinese scientists investigated more than 2,000 herbal recipes found in traditional Chinese medicine. So far so good – ayurveda proponents would be happy reading this. But read a bit more and the differences start to appear – the active compound was identified, the original extraction method didn’t work, only three treatments emerged while the rest were useless (I wonder if ayurveda proponents would do such a culling instead of making blanket assertions like “Ayurveda works”), even more powerful derivatives and combination treatments have been synthesized (i.e. they’re not “natural”), and crucially, the chemical mechanism of the drug is mostly known. This is a good example of Bayesian principles applied to medicine – the combination of a good prior probability and an overwhelming amount of data confirms that the drug works.

So what the scientists investigating ayurvedic substances should do is: (1) propose mechanisms i.e. HOW does the substance do what they claim it does and (2) do proper repeated trials to gather evidence that it does do what they say it does.



  1. Aditya says

    I am no fan of complementary and alternative medicine, but I do believe in giving credit where credit is due. The referenced paper was published in what seems to be a decent journal (plosone). This would indicate that it would have gone through a rigorous peer review process where they would have considered the plausibility of the results including your Bayesian analysis. Therefore, even if they do not comment on the causes and effects, the results cannot be simply discarded. Moreover, from the results and conclusion section, they did not seem to be making tall claims. Hence I do not see why the evidence they provide is insufficient.

    I do see the reason for your anguish from the original Hindu article. It has the typical overtones characteristic to Vedic apologists (hope this is the right word!). However criticizing published original research is a different matter all together. I have not gone through all the given links so do correct me if I am wrong or missing something.

  2. Arvind Raghavan says

    I’m actually quite open to Evidence-Based Medicine vs. a purely mechanistic approach. After all, anaerobic exercise was taboo for 70 years because there was no explanation for how lactic acid buildup was NOT damaging to muscles until the 1970s.

    Where I rush to agree: More than half of all published papers can’t be replicated in results. Yes, false positives are endemic, and only independently and repeatedly reproducible results should be accepted.

    Where I disagree: Should the basis for tolerance for acceptance of results always be “likelihood”? I agree, some prior probability needs to be introduced. But a Bayesian factor based on the mood of the times skews the results heavily towards current practices/norms, while what might be accepted 10 years from now may be quite different. Would it be a workable solution to have, as a tolerance metric, the possibility of harm? I.e, a study linking chamomile to relaxation (we have no solid hypothetical mechanism to explain this) showing positive results may be deemed more “tolerable” than a study showing positive results for heavy-metals in medicine.

    Yes, claims have to be repeatedly reproduced before they are incorporated. But I’m afraid “likelihood” biases us against things that just seem wonky. Like the notion that coconut oil has significant benefits, or that Ashwagandha/Tulsi may have adaptogenic benefits for cortisol-support etc.

  3. says

    @Arvind – I guess if we had infinite resources (money, time, scientists) then one could justify researching stuff that’s wonky (i.e. that has a low prior probability and scant evidence). But we don’t have infinite resources. The resources that the government of India and even reputed universities are spending on this stuff would better be spent elsewhere. Also, plausibility is not 100% must-have if there is strong experimental evidence of efficacy. The history of anaesthesia is a good example – we were using it long before the mechanism was known, the reason being there was strong evidence that it worked, and it would have been unethical to withhold it given its importance. So there’s nothing in SBM which says “when you have strong evidence of efficacy but you don’t know how it’s working, don’t investigate any further”.

  4. lorn says

    One wonders how people who can object vehemently and unfairly against a few micrograms of mercury in a few vaccines can avoid burning outrage over the thousands of times more mercury, and other heavy metals in a single dose of many Ayurvedic medicines.

  5. Rabidtreeweasel says

    Vastu ayurveda really gets my ire up as well. When hearing someone, an “expert,” touting the benefits of entering your house from the East as opposed to any other direction, and claiming this was based in “universal natural laws” brought up from the Ved, my response was, “What’s the causality?” He hemmed and hawed, trying to lean on, “Well, it comes from the Ved, so that’s the predictive basis.” My follow up was, “Great, so how do you test why the demons don’t enter through the eastern facing houses? Because that’s what it says in the Ved, right? And if this is based on universal law, then what is the universal principle? If we traveled to a distant planet with a different star, what direction should we face the entrance of our pods? Are there space demons that we need to be watchful of?” I said it in a MUCH nicer way, but he still was flustered an annoyed. And that’s why no one should EVER go to MUM or practice TM. Because those people are CRAZY and don’t even know how to defend their homes against aliens in space.

  6. Rama Rao K says

    If any CAM formulation really works, then it no longer becomes CAM but mainstream medicine. Just like we don’t have Physics and Alternate Physics or Maths, there should be no such thing as Alternate Medicine. Either the medicine works or it doesn’t. Any medicine/treatment based on evidence should be accepted until such time that a more credible evidence to the contrary doesn’t appear.

  7. Arvind Raghavan says

    Well of course, in matters of allocating funds, one needs to have some, any (even flawed), metric to ascertain where the money is best spent. But this article is not about how best to allocate funds (indeed, many decision-makers might admit that their fund-distribution is based on a lot more than just statistical data, and a lot of subjective opinion too). If that is the only aspect, then yes, I’d agree with you. I’m assuming this article is also about how to interpret and use the results of research/trials.

    The objective of research, surely, isn’t merely to confirm what our preconceptions are (which is literally what a Bayesian coefficient would do). It’s to maintain strict fidelity to the data, and to be agnostic about what is “plausible” and what is not.

    Of course, one shouldn’t make prescriptions based solely on one study. But take a controversial issue like vitamin C’s effect on cancer. It needs repeated and reproducible results. How does one attribute a prior probability to it, given wildly differing “expert” views on the matter? And undue skepticism might cost lives, when the worst case scenario is that you spend more on a useless injection (Pascal’s wager, basically).

    Additionally, the concept of P-value of a study is not without its own critics (

  8. Chetan Padliya says

    The biggest mistake we are doing is comparison. Both systems are totally different, Ayurveda is way of life it emphasise on prevention of diseases. E.g. How, when and what you eat is more important in ayurveda and if you follow whatever mention in Ayurveda text books you can live a healthy life. Ayurveda is everywhere in your life, if you are healthy it guide you to maintain your health an if you are I’ll it helps you to get rid of disease the help of medicines and by correcting your way of life.
    No doubt modern system of medicine is very advance to cure the fatal diseases and in surgery, but comparing both system is totally unfair. We should take advantage of both, rather critisizing one.

  9. Arvind Raghavan says

    ^Mr. Padliya,

    Ayurveda isn’t a way of life. You’re right, it is a system that focuses on (it claims) holistic well-being. It should not be treated any different from other forms of medicine, which are all intensely scrutinized and critically examined.

    “If you follow whatever you mention in Ayurveda text books you can live a healthy life” –> Why should I accept this statement, based solely on some authority or anecdotal evidence? It all boils down to whether there is double-blind tested evidence that shows it works. Otherwise, we have no reason to believe Ayurveda’s claims of 3 doshas, panchakosha, toxic-metal medicines etc. are any better than other discredited systems of medicine.

  10. Chetan Padliya says

    Mr Raghavan,
    Ayurveda is not only a system of medicines, medicines are only a part of Ayurveda.
    Ayurveda is time tested system of healthy life style. I think again you are making mistake by comparing it with modern system of medicines. I want to explain with a simple example, if a patient has constipation and goes to allopathic doctor he will prescribe laxatives which gives only temporary relief and once you stop taking medicines problem will be same as before while a ayurvedic doctor will suggest you a healthy life style like drink planty of water after getup in the morning, avoide excessive tea and coffee, eat fiber rich food, go for walk and take ispagula husk in the night if required.
    As far as question of toxic-metal medicines, its true that this medicines are dangerous because cos do not make properly accordind to procedure and unfortunately there is no regulatory body take strict against manufacture of such wrongfully prepared medicines. Actually if correct procedure is followed to prepare a medicine contain heavy metals it convert into salt of that metal and in modern medicines too so many salt of metals are in use.
    3 dosha is also a very perfect way of diagnosis, just try on yourself and find which dosha is disturbed in your body and get solution to calm that dosha you will get relief.
    I am not an ayurveda professional, I m a pharmacy graduate and deal in modern medicine but whenever i become ill i try to find a ayurveda solution to get well and use modern medicine only in some emmergency cases.

  11. Arvind Raghavan says

    Mr. Padliya,

    I repeat, why should anyone accept a medical system just because it has lasted for a long time? There are many schools of medicine which entire civilizations considered “time tested” that they strongly believed in for thousands of years, such as the practice of applying leeches, bleeding a patient who had fever etc. Traditional Chinese Medicine and homeopathy is still immensely popular, despite most of its claims being debunked in laboratories. Why should Ayurveda be treated any different?

    High fiber, exercise, less sugar, more coloured vegetables, proper sleep…these are not Ayurvedic. Those are just common heart-healthy guidelines that have scientific backing, which all doctors should be prescribing. If there is a claim specifically by Ayurvedic doctors, it needs to first be demonstrated in research.

    Perfect example is the claim of doshas. I have tried it, and from very reputed institutions. It hasn’t worked. Some people claim it works, but anecdotes don’t count as evidence in a lab. Which is why it needs to be scrutinized and critically evaluated instead of blindly accepting it.

  12. chetan padliya says

    Mr Raghavan
    Why not we should believe any system of medicine which is treating generation over generations. Again I repeat its not only about medicines, Medicines are part of Ayurveda. Ayurveda include so many things like yoga, food habits, compatible and incompatible foods which prevents and caused so many diseases, how and when to sleep and so many little things which are part of our daily life. It all mention in ancient Ayurveda text book so one cant say that its just guidelines everybody knows, its all already mention in ancient text.
    There are so many Ayurvedic medicines have proved its efficacy in clinical trials.
    Might be all claims not proved in laboratory but already effectively serving mankind from long time. Ayurveda is totally a natural system and in nature also there are so may mysteries unsolved but exist.
    No doubt In today’s modern era due to quick result required and unfortunately unavailability of pure herbs question are raised on Ayurveda but still its a system trusted by a big population.
    Still if you just want to compare herbal medicine with chemical medicines in laboratory on same parameter to trust on wont be justified.
    I just try to apply ayurveda concepts in my day to day life and definitely it makes difference in my life and help me to live my life healthy so it depends how one use Ayurveda knowledge in his life.
    Ayurveda and modern medicines can’t be substitute of each other both have its advantage and disadvantage.

  13. Prabhu G says

    Atleast as customer what i would worry is whether it works.Whether it’s efficacy is proved through double blind trails.Ayurveda being there for 3000yrs , it wasn’t able to solve fever,small pox,chicken pox,cholera etc… I am little skeptical about ayurveda’s capability solving other issues(Assuming these were very common diseases of the past).I am o.k with medicines through double blind trials

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