The ScienceBasedMedicine.org Reference Pages are reviews of topics relevant to science and medicine. Each consists of a concise overview of the topic from a scientific perspective, an index of the most relevant posts here on SBM, links to some external resources we recommend, and our summaries of the most interesting and important research. These pages are a work in progress, and we are actively developing them over the summer and fall of 2013, starting with acupuncture, chiropractic, homeopathy, and vaccines & autism.

Overview of Homeopathy

Homeopathy was invented by Samuel Christian Hahnemann (1755-1843), a German physician who had become dissatisfied with the medicine of his day. Hahnemann lived in a time before the rudiments of modern medicine had been developed, before the germ theory of infectious disease, before the first antibiotic, before systematic testing of drugs for safety and efficacy, before surgical procedures were performed with anesthesia or sterile technique.

For many years Hahnemann’s search was unsuccessful, until he stumbled upon what he thought was an amazing observation: he took a small amount of cinchona bark, which contains quinine, the drug used to treat malaria, and developed the symptoms of malaria. From this observation he developed homeopathy’s first law, “similia similibus curentur,” or let likes be cured by likes. In other words, drugs which cause specific symptoms can be used to cure diseases which cause the same symptoms.

As homeopathy evolved, other “laws” were also discovered. The law of infinitesimal doses was actually a late development by Hahnemann, but today is often thought of as the primary characteristic of homeopathy. This law states that when drugs are diluted in either water or alcohol, they actually increase in therapeutic potency. Today, serial dilutions of 1:100 repeated 6 or 30 times are commonly used. Between each dilution the substance is violently shaken, which is thought to be necessary to activate the properties of the drug.

Hahnemann also developed, as the underpinning of homeopathy, his own theory of disease, called the miasm theory. According to this theory there are three miasms which are responsible for all human disease, and homeopathic remedies are directed towards treating these offending miasms.

The goal of a homeopathic consultation is to find the “totality of symptoms,” physical, mental, and spiritual. They accomplish this goal by taking a “homeopathic history” which includes questions such as: do you feel sad when you hear piano music, are you excessively tidy, or do you have a chilly personality? This information is combined with the patient’s symptoms and their physical “constitution,” which may depend on such facts as hair color. The homeopath then decides on what single remedy will treat the patient’s “totality.” The remedy is then prescribed, and is usually given in either a single dose or only a few doses.

The principles of homeopathy run contrary to modern science and have never been empirically established.

Homeopathic “provings” are a method of establishing what a homeopathic remedy contains and how diluted it should be. It is a sort of “in-house” scientific method, and a poor one: provings contains no controls for bias or any method for separating the ordinary experiences of daily life from true symptoms caused by the substance being tested. Many of the provings used to guide homeopathic treatment today were conducted by Samuel Hahneman himself. Subsequent efforts to demonstrate consistency or reproducibility of homeopathic provings have been unsuccessful.

The so-called law of similars, for example, is little more than an ancient and common superstition known as sympathetic magic — that things have an essence or essential quality that can be transferred. There is no scientific knowledge about biology or chemistry to support the notion that a small dose of a drug or substance will necessarily cause the symptoms it treats at higher doses.

Modern homeopaths have tried to justify the law of similars by comparing it to the effectiveness of vaccines — which involve giving small doses of an infectious pathogen to prevent a later infection. However, this analogy is not apt. Vaccines involve measurable doses of attenuated or killed organisms or their proteins, and operate by a known mechanism — they trigger an immune response. There is no analogy to homeopathic treatments.

The law of  infinitesimal doses also runs contrary to chemistry, pharmacology, and thermodynamics. Homeopaths today use dilutions of substances which essentially remove all traces of the substance from the final dilution. There is not likely to be even a single molecule of the original drug in the final remedy which is given to the patient. Homeopaths conclude from this fact that the substance is transferring its essence to the water into which it is diluted. The more it is diluted, the more potent is the water. They offer, however, no possible explanation for how simple water molecules can contain the essence of far more complex substances.

Modern homeopaths have also tried to rescue the notion of infinitessimals by invoking the concept of water memory. They claim that water molecules can form a structure that contains the information of the homeopathic remedy. However, such claims are fanciful to the point of invoking magic and are devoid of any evidence. Water structure is very transient and ephemeral. They last moments and could not survive repeated dilution, let alone ingestion, absorption into the body, and transport to whatever their alleged site of action is.

Other theories for how ultradilute remedies could have biological effects include the effects of nanoparticles supposedly detected in homeopathic solutions. However, the experiments purporting to identify these particles have been poorly conducted and subject to contamination and other sources of error, and only proponents of homeopathy believe this theory to have any substance. Similarly, homeopaths sometimes refer to the strange and counterintuitive theories of quantum mechanics as validating the implausible foundations of homeopathy. Unlike the “laws” of homeopathy, however, the fundamental theories of quantum physics have been demonstrated scientifically. The fact that some strange ideas have turned out to be true does not validate the theories of homeopathy, which have failed to produce convincing experimental evidence for 150 years.

Hahnemann developed his ideas before the disease theory of illness was fully developed. In other words, during his time physicians did not yet understand that illnesses were caused by specific diseases; that a given disease, such as diabetes, has a common underlying pathophysiology — a specific malfunction of a specific tissue, organ, or organ system leading to a specific disorder with recognizable signs and symptoms. This modern theory of illness has lead, for instance, to the treatment of diabetes with insulin replacement, vastly improving the quality and duration of life of patients suffering from this disease.

At this point many defenders of homeopathy would argue, “Who cares how it works, as long as it works.” There is a kernel of legitimacy to this argument (although it does not save homeopathy from being a pseudoscience) in that even in conventional medicine, treatments are often used before their mechanism of action is fully understood. There is a difference, however, between not fully understanding a mechanism and, as with homeopathy, violating basic laws of physics.  In such cases it is necessary to demonstrate using carefully controlled clinical trials that such treatments do in fact work.

There has been mixed results from clinical studies of homeopathy, but a clear trend when all the evidence is reviewed — the better designed the study the less likely there is to be any effect, and the best designed studies are negative. Homeopathy, it turns out, is no more effective than placebo (an inactive treatment).

Therefore, according to everything we currently understand about biology, chemistry, and physics homeopathy is highly implausible and should not work. And, when we carefully study homeopathic remedies they in fact do not work.

Given that most homeopathic remedies contain little if any actual ingredients beyond water and sometimes sugar, it is unlikely that any direct harm could come from taking them. Improper preparation of remedies made from toxic or infectious material could pose some risk, and there have been reports of toxic contamination of homeopathic products.

However, the most significant risk of homeopathy is that it often delays the use of accurate scientific diagnosis and truly effective medical treatment. Unnecessary injury, disability, and even death can result from the delusion that homeopathy is an effective treatment for any medical condition.

Index of SBM Posts about Homeopathy

Summary of Key Research about Homeopathy

The Law of Similars & Provings

Dantas F, Fisher P., Walach H., et al.  A systematic review of the quality of homeopathic pathogenetic trials published in the United Kingdom from 1945 to 1995. Homeopathy. 2007;96(1):4-16.

This study reviewed hundreds of proving trials from all over the world and found that these trials were poorly designed and conducted and were at such high risk of bias that it was not possible to trust the results. The basic idea that homeopathic preparations cause consistent symptoms in healthy volunteers could not be established.

Brien S, Prescott P, Owen D, Lewith G.  How do homeopaths make decisions? An exploratory study of inter-rater reliability and intuition in the decision making process. Homeopathy. 2004 Jul;93(3):125-31.

This study evaluated the consistency and reliability of homeopaths conducting a replication of a proving. It found little agreement between the individual homeopaths and a heavy reliance on intuition in judgments about the effects of the substance tested. 

Fisher P, Dantas F.  Homeopathic pathogenetic trials of Acidum malicum and Acidum ascorbicum. British Journal of Homeopathy. 2001;90:118–125.

In this proving, when investigators were properly blinded to whether subjects were given a homeopathic preparation or a placebo, the symptoms reported by volunteers occurred as often when taking he placebo as when taking the homeopathic remedy. 

Sarah Brien, George Lewith, and Trevor Bryant.  Ultramolecular homeopathy has no observable clinical effects. A randomized, double-blind, placebo-controlled proving trial of Belladonna 30C. British Journal of Clinical Pharmacology. 2003;56(5):562–568.

This study also controlled better than most provings for bias and found, again, that the homeopathy remedy had no apparent effects on healthy subjects.

Other such studies have failed to demonstrate any effect of homeopathic substances on healthy volunteers, as would be expected if the Law of Similars were correct.

Potentization by Dilution and Succussion (The “Law of Infinitessimals”)

Quite a few studies have attempted to show that ultradilute substances have meaningful biological effects. These attempts have not been very successful.

Becker-Witt C, Weisshuhn TE, Lüdtke R, Willich SN.  Quality assessment of physical research in homeopathy. Journal of Alternative and Complementary Medicine. 2003;9(1):113-32.

Even this friendly review of studies attempting to support the implausible premise of ultadilute remedies concluded the research was too poor in quality to actually draw any conclusions:

Most physical experiments of homeopathic preparations were performed with inadequate controls or had other serious flaws that prevented any meaningful conclusion. Except for those of high quality, all experiments should be repeated using stricter methodology and standardization before they are accepted as indications of special features of homeopathic potencies.

Vickers AJ.  Independent replication of pre-clinical research in homoeopathy: a systematic review. Forschende Komplementarmedezin. 1999;6:311-20.

A critical element in establishing the truth of a hypothesis in science is being able to reproduce the results of an experiment. If only a believer in an idea can get it to work in a scientific study, that is a strong indication of bias. This review of the research intended to support the basic principles of homeopathy concluded that such replication has not been accomplished despite over a century of research in the field:

There is a lack of independent replication of any pre-clinical research in homoeopathy. In the few instances where a research team has set out to replicate the work of another, either the results were negative or the methodology was questionable.

One of the few studies published in the mainstream medical literature concerning ultradilute homeopathic remedies, published in Nature in 1988, purported to show that such a remedy could influence the degranulation of human basophils.

Davenas E, Beauvais F, Amara J, Oberbaum M, Robinzon B, Miadonna A, Tedeschi A, Pomeranz B, Fortner P, Belon P, et al.  Human basophil degranulation triggered by very dilute antiserum against IgE. Nature. 1988 Jun 30;333(6176):816-8.

Because the findings were so revolutionary, the journal took the unprecedented step of arranging for an independent team of investigators to observe replications of the experiment. 

This team found that the results had been generated by an unblinded technician, and when this individual was unaware of the treatment given to each sample, the positive findings disappeared.

Maddox, J. Randi, J. Stewart, W.  “High-dilution” experiments a delusion. Nature 1988;334:287-290.

We conclude that the claims made by Davenas et al. are not to be believed. Our conclusion, not based solely on the circumstance that the only strictly doubleblind experiments we had witnessed proved to be failures, may be summarized as follows:

The care with which the experiments reported have been carried out does not match the extraordinary character of the claims made in their interpretation.

The phenomena described are not reproducible, but there has been no serious investigation of the reasons.

The data lack errors of the magnitude that would be expected, and which are unavoidable.

No serious attempt has been made to eliminate systematic errors, including observer bias.

The climate of the laboratory is inimical to an objective evaluation of the exceptional data.

Subsequently, multiple attempts by independent researchers to replicate the original experiment also failed to find an effect. A review published in a homeopathy journal in 2009 concluded that after twenty years of research, it was still impossible to determine conclusively that purported effects of ultradilute solutions on human basophils were not due solely to artifact.

Ennis, M.  Basophil models of homeopathy: a sceptical view. Homeopathy 2010;99(1):51–56.

Clinical Trials

Despite its deep and persistent implausibility and the lack of any sound reason to believe homeopathy could work, it has been the subject of hundreds of clinical trials. There have been so many studies that not only are there multiple systematic reviews of these trials, there are systematic reviews of the systematic reviews. Not surprisingly, the balance of the evidence does not indicate homeopathy is anything other than a placebo.

Ernst E.  A systematic review of systematic reviews of homeopathy. British Journal of Clinical Pharmacology. 2002;54:577-582.

The conclusion of this review was clear; the evidence does not support claims that homeopathy is anything other than a placebo:

Eleven independent systematic reviews were located. Collectively they failed to provide strong evidence in favour of homeopathy. In particular, there was no condition which responds convincingly better to homeopathic treatment than to placebo or other control interventions. Similarly, there was no homeopathic remedy that was demonstrated to yield clinical effects that are convincingly different from placebo.

It is concluded that the best clinical evidence for homeopathy available to date does not warrant positive recommendations for its use in clinical practice.

This review examined seventeen other reviews of clinical trials in homeopathy. Six of these were re-analyses of one famous review which appeared to support that homeopathy was more than just a placebo.

Linde K, Clausius N, Ramirez G, Melchart D, Eitel F, Hedges L V et al.  Are the clinical effects of homoeopathy placebo effects? A meta-analysis of placebo-controlled trials. Lancet. 1997;50:834-843.

The best this supposedly positive review could say was that while homeopathy did not appear effective for any specific medical problem, it looked like it might have some effects beyond that of a placebo.

The results of our meta-analysis are not compatible with the hypothesis that the clinical effects of homeopathy are completely due to placebo. However, we found insufficient evidence from these studies that homeopathy is clearly efficacious for any single clinical condition.

However, even this tepid conclusion did not stand up to further analysis, which revealed that this apparent effect was an illusion created by the inclusion of poor quality studies with inadequate controls for bias in the initial review. When the original authors re-analyzed their own work, they showed that the better one controls for bias, the less likely one is to see any effect of homeopathy, exactly as one would expect if homeopathy is a placebo.

Linde K, Scholz M, Ramirez G, Clausius N, Melchart D, Jonas WB.  Impact of study quality on outcome in placebo controlled trials of homoeopathy. Journal of Clinical Epidemiology. 1999;52:631-636.

Studies that were explicitly randomized and were double-blind as well as studies scoring above the cut-points yielded significantly less positive results than studies not meeting the criteria…We conclude that in the study set investigated, there was clear evidence that studies with better methodological quality tended to yield less positive results.

Several other re-analyses of these same data have been done, and all the independent analyses agreed that the appearance of effects greater than placebo was related to the inclusion of poor-quality studies in the original paper. 

The most recent review has specifically compared studies of homeopathic treatments with matched studies of conventional therapies to identify whether a clear effect beyond placebo could be seen for either. The conclusion was that while all clinical trials are imperfect, it is possible to distinguish a true therapeutic effect from placebo effects for conventional therapies but not for homeopathic treatment.

Shang A, Huwiler-Muntener K, Nartey L, et al.  Are the clinical effects of homoeopathy placebo effects? Comparative study of placebo-controlled trials of homoeopathy and allopathy. Lancet 2005; 366:726-732.

Biases are present in placebo-controlled trials of both homoeopathy and conventional medicine. When account was taken for these biases in the analysis, there was weak evidence for a specific effect of homoeopathic remedies, but strong evidence for specific effects of conventional interventions. This finding is compatible with the notion that the clinical effects of homoeopathy are placebo effects.

Risks of Homeopathy

Freckelton I.  Death by homeopathy: Issues for civil, criminal, and coronial law and for health service policy. Journal of Law and Medicine. 2012;19(3):454-478.

This review of the legal issues involving regulation of homeopathy considers the ethical implications of the lack of scientific proof homeopathy is anything more than a placebo and the real risk facing patients if governments support this delusion by regulating the practice as if it were a legitimate medical therapy.

recent years have seen a series of meta-analyses that have suggested that the therapeutic claims of homeopathy lack scientific justification. criminal and coronial decisions have reached deeply troubling conclusions about homoeopaths and the risk that they pose for counter-therapeutic outcomes, including the causing of deaths. The legal decisions, in conjunction with the recent analyses of homoeopathy’s claims, are such as to raise confronting health care and legal issues relating to matters as diverse as consumer protection and criminal liability. They suggest that the profession is not suitable for formal registration and regulation lest such a status lend to it a legitimacy that it does not warrant.

Summaries of key research by Brennen McKenzie, the SkeptVet.