Homeopathy

Homeopathy () or homoeopathy is a system of alternative medicine created in 1796 by Samuel Hahnemann, based on his doctrine of "like cures like" ("similia similibus curentur"), a claim that a substance that causes the symptoms of a disease in healthy people would cure similar symptoms in sick people. Homeopathy is a pseudoscience – a belief that is incorrectly presented as scientific. Homeopathic preparations are not effective for treating any condition; large-scale studies have found homeopathy to be no more effective than a placebo, suggesting that any positive feelings that follow treatment are only due to the placebo effect and normal recovery from illness.
Hahnemann believed the underlying causes of disease were phenomena that he termed "miasms", and that homeopathic preparations addressed these. The preparations are manufactured using a process of homeopathic dilution, in which a chosen substance is repeatedly diluted in alcohol or distilled water, each time with the containing vessel being bashed against an elastic material, (commonly a leather-bound book). Dilution typically continues well past the point where no molecules of the original substance remain. Homeopaths select homeopathics by consulting reference books known as "repertories", and by considering the totality of the patient's symptoms, personal traits, physical and psychological state, and life history.
Homeopathy is not a plausible system of treatment, as its dogmas about how drugs, illness, the human body, liquids and solutions operate are contradicted by a wide range of discoveries across biology, psychology, physics and chemistry made in the two centuries since its invention. Although some clinical trials produce positive results, multiple systematic reviews have indicated that this is because of chance, flawed research methods, and reporting bias. Continued homeopathic practice, despite the evidence that it does not work, has been criticized as unethical because it discourages the use of effective treatments, with the World Health Organization warning against using homeopathy to try to treat severe diseases such as HIV and malaria. The continued practice of homeopathy, despite a lack of evidence of efficacy, has led to it being characterized within the scientific and medical communities as nonsense, quackery, and a sham.
Assessments by the Australian National Health and Medical Research Council, the United Kingdom's House of Commons Science and Technology Committee and the Swiss Federal Health Office have each concluded that homeopathy is ineffective, and recommended against the practice receiving any further funding.
In 2016 the United States FTC issued an "Enforcement Policy Statement Regarding Marketing Claims for Over-the-Counter Homeopathic Drugs" which specified that the FTC will hold efficacy and safety claims for OTC homeopathic drugs to the same standard as other products making similar claims. An accompanying FTC press release stated that for the vast majority of OTC homeopathic drugs, there are no valid studies using current scientific methods showing the product’s efficacy, and that "homeopathic theories are not accepted by most modern medical experts."
Homeopaths claim that Hippocrates may have originated homeopathy around 400 BC, when he prescribed a small dose of mandrake root to treat mania, knowing it produces mania in much larger doses. In the 16th century, the pioneer of pharmacology Paracelsus declared that small doses of "what makes a man ill also cures him". Samuel Hahnemann (1755–1843) gave homeopathy its name and expanded its principles in the late 18th century.
In the late 18th and 19th centuries, mainstream medicine used methods like bloodletting and purging, and administered complex mixtures, such as Venice treacle, which was made from 64 substances including opium, myrrh, and viper's flesh. These treatments often worsened symptoms and sometimes proved fatal. Hahnemann rejected these practices – which had been extolled for centuries – as irrational and inadvisable;
instead, he advocated the use of single drugs at lower doses and promoted an immaterial, vitalistic view of how living organisms function, believing that diseases have spiritual, as well as physical causes.
The term "homeopathy" was coined by Hahnemann and first appeared in print in 1807.
Hahnemann conceived of homeopathy while translating a medical treatise by the Scottish physician and chemist William Cullen into German. Being sceptical of Cullen's theory concerning cinchona's use for curing malaria, Hahnemann ingested some bark specifically to investigate what would happen. He experienced fever, shivering and joint pain: symptoms similar to those of malaria itself. From this, Hahnemann came to believe that all effective drugs produce symptoms in healthy individuals similar to those of the diseases that they treat, in accord with the "law of similars" that had been proposed by ancient physicians. An account of the effects of eating cinchona bark noted by Oliver Wendell Holmes, and published in 1861, failed to reproduce the symptoms Hahnemann reported. Hahnemann's law of similars is a postulate rather than a scientific law. This led to the name "homeopathy", which comes from the "hómoios", "-like" and "páthos", "suffering")
Subsequent scientific work showed that cinchona cures malaria because it contains quinine, which kills the "Plasmodium falciparum" parasite that causes the disease; the mechanism of action is unrelated to Hahnemann's ideas.
Hahnemann began to test what effects substances produced in humans, a procedure that would later become known as "homeopathic proving". These tests required subjects to test the effects of ingesting substances by clearly recording all of their symptoms as well as the ancillary conditions under which they appeared. He published a collection of provings in 1805, and a second collection of 65 preparations appeared in his book, "Materia Medica Pura", in 1810.
Because Hahnemann believed that large doses of drugs that caused similar symptoms would only aggravate illness, he advocated extreme dilutions of the substances; he devised a technique for making dilutions that he believed would preserve a substance's therapeutic properties while removing its harmful effects. Hahnemann believed that this process aroused and enhanced "the spirit-like medicinal powers of the crude substances".
He gathered and published a complete overview of his new medical system in his 1810 book, "The Organon of the Healing Art", whose 6th edition, published in 1921, is still used by homeopaths today.
In the "Organon", Hahnemann introduced the concept of "miasms" as "infectious principles" underlying chronic disease. Hahnemann associated each miasm with specific diseases, and thought that initial exposure to miasms causes local symptoms, such as skin or venereal diseases. If, however, these symptoms were suppressed by medication, the cause went deeper and began to manifest itself as diseases of the internal organs. Homeopathy maintains that treating diseases by directly alleviating their symptoms, as is sometimes done in conventional medicine, is ineffective because all "disease can generally be traced to some latent, deep-seated, underlying chronic, or inherited tendency". The underlying imputed miasm still remains, and deep-seated ailments can be corrected only by removing the deeper disturbance of the vital force.
Hahnemann’s hypotheses for the direct or remote cause of all chronic diseases (miasms) originally presented only three, psora (the itch), syphilis (venereal disease) or sycosis (fig-wart disease). Of these three the most important was "psora" (Greek for "itch"), described as being related to any itching diseases of the skin, supposed to be derived from suppressed scabies, and claimed to be the foundation of many further disease conditions. Hahnemann believed psora to be the cause of such diseases as epilepsy, cancer, jaundice, deafness, and cataracts.
Since Hahnemann's time, other miasms have been proposed, some replacing one or more of psora's proposed functions, including tuberculosis and cancer miasms.
The law of susceptibility implies that a negative state of mind can attract hypothetical disease entities called "miasms" to invade the body and produce symptoms of diseases. Hahnemann rejected the notion of a disease as a separate thing or invading entity, and insisted it was always part of the "living whole". Hahnemann coined the expression "allopathic medicine", which was used to pejoratively refer to traditional Western medicine.
Hahnemann's miasm theory remains disputed and controversial within homeopathy even in modern times. The theory of miasms has been criticized as an explanation developed by Hahnemann to preserve the system of homeopathy in the face of treatment failures, and for being inadequate to cover the many hundreds of sorts of diseases, as well as for failing to explain disease predispositions, as well as genetics, environmental factors, and the unique disease history of each patient.
Homeopathy achieved its greatest popularity in the 19th century. It was introduced to the United States in 1825 by Hans Birch Gram, a student of Hahnemann. The first homeopathic school in the US opened in 1835, and in 1844, the first US national medical association, the American Institute of Homeopathy, was established. Throughout the 19th century, dozens of homeopathic institutions appeared in Europe and the United States, and by 1900, there were 22 homeopathic colleges and 15,000 practitioners in the United States. Because medical practice of the time relied on ineffective and often dangerous treatments, patients of homeopaths often had better outcomes than those of the doctors of the time. Homeopathic preparations, even if ineffective, would almost surely cause no harm, making the users of homeopathic preparations less likely to be killed by the treatment that was supposed to be helping them. The relative success of homeopathy in the 19th century may have led to the abandonment of the ineffective and harmful treatments of bloodletting and purging and to have begun the move towards more effective, science-based medicine.
One reason for the growing popularity of homeopathy was its apparent success in treating people suffering from infectious disease epidemics.
During 19th-century epidemics of diseases such as cholera, death rates in homeopathic hospitals were often lower than in conventional hospitals, where the treatments used at the time were often harmful and did little or nothing to combat the diseases.
From its inception, however, homeopathy was criticized by mainstream science. Sir John Forbes, physician to Queen Victoria, said in 1843 that the extremely small doses of homeopathy were regularly derided as useless, "an outrage to human reason". James Young Simpson said in 1853 of the highly diluted drugs: "No poison, however strong or powerful, the billionth or decillionth of which would in the least degree affect a man or harm a fly."
19th-century American physician and author Oliver Wendell Holmes, Sr. was also a vocal critic of homeopathy and published an essay in 1842 entitled "Homœopathy and Its Kindred Delusions". The members of the French Homeopathic Society observed in 1867 that some leading homeopathists of Europe not only were abandoning the practice of administering infinitesimal doses but were also no longer defending it. The last school in the US exclusively teaching homeopathy closed in 1920.
According to , the Nazi regime in Germany was fascinated by homeopathy, and spent large sums of money on researching its mechanisms, but without gaining a positive result. Unschuld further argues that homeopathy never subsequently took root in the United States, but remained more deeply established in European thinking.
In the United States, the "Food, Drug, and Cosmetic Act" of 1938 (sponsored by Royal Copeland, a Senator from New York and homeopathic physician) recognized homeopathic preparations as drugs. In the 1950s, there were only 75 pure homeopaths practising in the U.S. However, by the mid to late 1970s, homeopathy made a significant comeback and sales of some homeopathic companies increased tenfold. Some homeopaths give credit for the revival to Greek homeopath George Vithoulkas, who performed a "great deal of research to update the scenarios and refine the theories and practice of homeopathy", beginning in the 1970s, but Ernst and Singh consider it to be linked to the rise of the New Age movement. Whichever is correct, mainstream pharmacy chains recognized the business potential of selling homeopathic preparations. The Food and Drug Administration held a hearing April 20 and 21, 2015, requesting public comment on regulation of homeopathic drugs. The FDA cited the growth of sales of over the counter homeopathic medicines, $2.7 billion as of 2007, many labelled as "natural, safe, and effective".
Bruce Hood has argued that the increased popularity of homeopathy in recent times may be due to the comparatively long consultations practitioners are willing to give their patients, and to an irrational preference for "natural" products which people think are the basis of homeopathic preparations.
Homeopathic preparations are referred to as "homeopathics" or "remedies". Practitioners rely on two types of reference when prescribing: "materia medica" and repertories. A homeopathic "materia medica" is a collection of "drug pictures", organized alphabetically. These entries describe the symptom patterns associated with individual preparations. A homeopathic repertory is an index of disease symptoms that lists preparations associated with specific symptoms. In both cases different compilers may dispute particular inclusions. The first symptomatic homeopathic "materia medica" was arranged by Hahnemann. The first homeopathic repertory was Georg Jahr's "Symptomenkodex", published in German in 1835, and translated into English as the "Repertory to the more Characteristic Symptoms of Materia Medica" by Constantine Hering in 1838.
This version was less focused on disease categories and would be the forerunner to later works by James Tyler Kent. Repertories, in particular, may be very large.
Homeopathy uses animal, plant, mineral, and synthetic substances in its preparations, generally referring to them using Latin or faux-Latin names. Examples include "arsenicum album" (arsenic oxide), "natrum muriaticum" (sodium chloride or table salt), "Lachesis muta" (the venom of the bushmaster snake), "opium", and "thyroidinum" (thyroid hormone).
Some homeopaths use so-called "nosodes" (from the Greek "nosos", disease) made from diseased or pathological products such as fecal, urinary, and respiratory discharges, blood, and tissue. Conversely, preparations made from "healthy" specimens are called "sarcodes".
Some modern homeopaths use preparations they call "imponderables" because they do not originate from a substance but some other phenomenon presumed to have been "captured" by alcohol or lactose. Examples include X-rays
and sunlight.
Other minority practices include paper preparations, where the substance and dilution are written on pieces of paper and either pinned to the patients' clothing, put in their pockets, or placed under glasses of water that are then given to the patients, and the use of radionics to manufacture preparations. Such practices have been strongly criticized by classical homeopaths as unfounded, speculative, and verging upon magic and superstition.
Hahnemann found that undiluted doses caused reactions, sometimes dangerous ones, so specified that preparations be given at the lowest possible dose. He found that this reduced potency as well as side-effects, but formed the view that vigorous shaking and striking on an elastic surface – a process he termed "Schütteln", translated as "succussion" – nullified this. A common explanation for his settling on this process is said to be that he found preparations subjected to agitation in transit, such as in saddle bags or in a carriage, were more "potent". Hahnemann had a saddle-maker construct a special wooden striking board covered in leather on one side and stuffed with horsehair. Insoluble solids, such as granite, diamond, and platinum, are diluted by grinding them with lactose ("trituration").
The process of dilution and succussion is termed "dynamization" or "potentization" by homeopaths. In industrial manufacture this may be done by machine.
Serial dilution is achieved by taking an amount of the mixture and adding solvent, but the "Korsakovian" method may also be used, whereby the vessel in which the preparations are manufactured is emptied, refilled with solvent, and the volume of fluid adhering to the walls of the vessel is deemed sufficient for the new batch. The Korsakovian method is sometimes referred to as K on the label of a homeopathic preparation, e.g. 200CK is a 200C preparation made using the Korsakovian method.
Fluxion and radionics methods of preparation do not require succussion. There are differences of opinion on the number and force of strikes, and some practitioners dispute the need for succussion at all while others reject the Korsakovian and other non-classical preparations. There are no laboratory assays and the importance and techniques for succussion cannot be determined with any certainty from the literature.
Three main logarithmic potency scales are in regular use in homeopathy. Hahnemann created the "centesimal" or "C scale", diluting a substance by a factor of 100 at each stage. The centesimal scale was favoured by Hahnemann for most of his life.
A 2C dilution requires a substance to be diluted to one part in 100, and then some of that diluted solution diluted by a further factor of 100.
This works out to one part of the original substance in 10,000 parts of the solution. A 6C dilution repeats this process six times, ending up with the original substance diluted by a factor of 100=10 (one part in one trillion or 1/1,000,000,000,000). Higher dilutions follow the same pattern.
In homeopathy, a solution that is more dilute is described as having a higher "potency", and more dilute substances are considered by homeopaths to be stronger and deeper-acting. The end product is often so diluted as to be indistinguishable from the diluent (pure water, sugar or alcohol). There is also a decimal potency scale (notated as "X" or "D") in which the preparation is diluted by a factor of 10 at each stage.
Hahnemann advocated 30C dilutions for most purposes (that is, dilution by a factor of 10). Hahnemann regularly used potencies up to 300C but opined that "there must be a limit to the matter, it cannot go on indefinitely".
In Hahnemann's time, it was reasonable to assume the preparations could be diluted indefinitely, as the concept of the atom or molecule as the smallest possible unit of a chemical substance was just beginning to be recognized.
The greatest dilution reasonably likely to contain even one molecule of the original substance is 12C.
Critics and advocates of homeopathy alike commonly attempt to illustrate the dilutions involved in homeopathy with analogies.
Hahnemann is reported to have joked that a suitable procedure to deal with an epidemic would be to empty a bottle of poison into Lake Geneva, if it could be succussed 60 times.
Another example given by a critic of homeopathy states that a 12C solution is equivalent to a "pinch of salt in both the North and South Atlantic Oceans", which is approximately correct.
One-third of a drop of some original substance diluted into all the water on earth would produce a preparation with a concentration of about 13C. A popular homeopathic treatment for the flu is a 200C dilution of duck liver, marketed under the name Oscillococcinum. As there are only about 10 atoms in the entire observable universe, a dilution of one molecule in the observable universe would be about 40C. Oscillococcinum would thus require 10 more universes to simply have one molecule in the final substance.
The high dilutions characteristically used are often considered to be the most controversial and implausible aspect of homeopathy.
Not all homeopaths advocate high dilutions. Preparations at concentrations below 4X are considered an important part of homeopathic heritage. Many of the early homeopaths were originally doctors and generally used lower dilutions such as "3X" or "6X", rarely going beyond "12X".
The split between lower and higher dilutions followed ideological lines.
Those favouring low dilutions stressed pathology and a stronger link to conventional medicine, while those favouring high dilutions emphasized vital force, miasms and a spiritual interpretation of disease.
Some products with such relatively lower dilutions continue to be sold, but like their counterparts, they have not been conclusively demonstrated to have any effect beyond that of a placebo.
A homeopathic "proving" is the method by which the profile of a homeopathic preparation is determined.
At first Hahnemann used undiluted doses for provings, but he later advocated provings with preparations at a 30C dilution, and most modern provings are carried out using ultra-dilute preparations in which it is highly unlikely that any of the original molecules remain. During the proving process, Hahnemann administered preparations to healthy volunteers, and the resulting symptoms were compiled by observers into a "drug picture".
The volunteers were observed for months at a time and made to keep extensive journals detailing all of their symptoms at specific times throughout the day. They were forbidden from consuming coffee, tea, spices, or wine for the duration of the experiment; playing chess was also prohibited because Hahnemann considered it to be "too exciting", though they were allowed to drink beer and encouraged to exercise in moderation.
After the experiments were over, Hahnemann made the volunteers take an oath swearing that what they reported in their journals was the truth, at which time he would interrogate them extensively concerning their symptoms.
Provings are claimed to have been important in the development of the clinical trial, due to their early use of simple control groups, systematic and quantitative procedures, and some of the first application of statistics in medicine. The lengthy records of self-experimentation by homeopaths have occasionally proven useful in the development of modern drugs: For example, evidence that nitroglycerin might be useful as a treatment for angina was discovered by looking through homeopathic provings, though homeopaths themselves never used it for that purpose at that time.
The first recorded provings were published by Hahnemann in his 1796 "Essay on a New Principle".
His "Fragmenta de Viribus" (1805) contained the results of 27 provings, and his 1810 "Materia Medica Pura" contained 65.
For James Tyler Kent's 1905 "Lectures on Homoeopathic Materia Medica", 217 preparations underwent provings and newer substances are continually added to contemporary versions.
Though the proving process has superficial similarities with clinical trials, it is fundamentally different in that the process is subjective, not blinded, and modern provings are unlikely to use pharmacologically active levels of the substance under proving. As early as 1842, Holmes noted the provings were impossibly vague, and the purported effect was not repeatable among different subjects.
Homeopaths generally begin with detailed examinations of their patients' histories, including questions regarding their physical, mental and emotional states, their life circumstances and any physical or emotional illnesses. The homeopath then attempts to translate this information into a complex formula of mental and physical symptoms, including likes, dislikes, innate predispositions and even body type.
From these symptoms, the homeopath chooses how to treat the patient using "materia medica" and repertories. In classical homeopathy, the practitioner attempts to match a single preparation to the totality of symptoms (the "simlilum"), while "clinical homeopathy" involves combinations of preparations based on the various symptoms of an illness.
Homeopathic pills are made from an inert substance (often sugars, typically lactose), upon which a drop of liquid homeopathic preparation is placed and allowed to evaporate.
The process of homeopathic dilution results in no objectively detectable active ingredient in most cases, but some preparations (e.g. calendula and arnica creams) do contain pharmacologically active doses. One product, Zicam Cold Remedy, which was marketed as an "unapproved homeopathic" product, contains two ingredients that are only "slightly" diluted: zinc acetate (2X = 1/100 dilution) and zinc gluconate (1X = 1/10 dilution), which means both are present in a biologically active concentration strong enough to have caused some people to lose their sense of smell, a condition termed anosmia. Zicam also listed several normal homeopathic potencies as "inactive ingredients", including "galphimia glauca", histamine dihydrochloride (homeopathic name, "histaminum hydrochloricum"), "luffa operculata", and sulfur.
Isopathy is a therapy derived from homeopathy, invented by Johann Joseph Wilhelm Lux in the 1830s. Isopathy differs from homeopathy in general in that the preparations, known as "nosodes", are made up either from things that cause the disease or from products of the disease, such as pus. Many so-called "homeopathic vaccines" are a form of isopathy.
Flower preparations can be produced by placing flowers in water and exposing them to sunlight. The most famous of these are the Bach flower remedies, which were developed by the physician and homeopath Edward Bach. Although the proponents of these preparations share homeopathy's vitalist world-view and the preparations are claimed to act through the same hypothetical "vital force" as homeopathy, the method of preparation is different. Bach flower preparations are manufactured in allegedly "gentler" ways such as placing flowers in bowls of sunlit water, and the preparations are not succussed. There is no convincing scientific or clinical evidence for flower preparations being effective.
The idea of using homeopathy as a treatment for other animals termed "veterinary homeopathy", dates back to the inception of homeopathy; Hahnemann himself wrote and spoke of the use of homeopathy in animals other than humans. The FDA has not approved homeopathic products as veterinary medicine in the U.S. In the UK, veterinary surgeons who use homeopathy may belong to the Faculty of Homeopathy and/or to the British Association of Homeopathic Veterinary Surgeons. Animals may be treated only by qualified veterinary surgeons in the UK and some other countries. Internationally, the body that supports and represents homeopathic veterinarians is the International Association for Veterinary Homeopathy.
The use of homeopathy in veterinary medicine is controversial; the little existing research on the subject is not of a high enough scientific standard to provide reliable data on efficacy. Other studies have also found that giving animals placebos can play active roles in influencing pet owners to believe in the effectiveness of the treatment when none exists. The British Veterinary Association's position statement on alternative medicines says that it "cannot endorse" homeopathy, and the Australian Veterinary Association includes it on its list of "ineffective therapies".
The UK's Department for Environment, Food and Rural Affairs (Defra) has adopted a robust position against use of "alternative" pet preparations including homeopathy.
Electrohomeopathy is a treatment devised by Count Cesare Mattei (1809–1896), who proposed that different "colours" of electricity could be used to treat cancer. Popular in the late nineteenth century, electrohomeopathy has been described as "utter idiocy".
The use of homeopathy as a preventive for serious infectious diseases is especially controversial, in the context of ill-founded public alarm over the safety of vaccines stoked by the anti-vaccination movement. Promotion of homeopathic alternatives to vaccines has been characterized as dangerous, inappropriate and irresponsible. In December 2014, Australian homeopathy supplier Homeopathy Plus! were found to have acted deceptively in promoting homeopathic alternatives to vaccines.
The low concentration of homeopathic preparations, which often lack even a single molecule of the diluted substance, has been the basis of questions about the effects of the preparations since the 19th century. Modern advocates of homeopathy have proposed a concept of "water memory", according to which water "remembers" the substances mixed in it, and transmits the effect of those substances when consumed. This concept is inconsistent with the current understanding of matter, and water memory has never been demonstrated to have any detectable effect, biological or otherwise. Pharmacological research has found instead that stronger effects of an active ingredient come from higher, not lower doses.
James Randi and the groups have highlighted the lack of active ingredients in most homeopathic products by taking large 'overdoses'. None of the hundreds of demonstrators in the UK, Australia, New Zealand, Canada and the US were injured and "no one was cured of anything, either".
Outside of the alternative medicine community, scientists have long considered homeopathy a sham or a pseudoscience, and the mainstream medical community regards it as quackery. There is an overall absence of sound statistical evidence of therapeutic efficacy, which is consistent with the lack of any biologically plausible pharmacological agent or mechanism.
Abstract concepts within theoretical physics have been invoked to suggest explanations of how or why preparations might work, including quantum entanglement, quantum nonlocality, the theory of relativity and chaos theory. Contrariwise, quantum superposition has been invoked to explain why homeopathy does "not" work in double-blind trials. However, the explanations are offered by nonspecialists within the field, and often include speculations that are incorrect in their application of the concepts and not supported by actual experiments. Several of the key concepts of homeopathy conflict with fundamental concepts of physics and chemistry. The use of quantum entanglement to explain homeopathy's purported effects is "patent nonsense", as entanglement is a delicate state which rarely lasts longer than a fraction of a second. While entanglement may result in certain aspects of individual subatomic particles acquiring linked quantum states, this does not mean the particles will mirror or duplicate each other, nor cause health-improving transformations.
The proposed mechanisms for homeopathy are precluded from having any effect by the laws of physics and physical chemistry. The extreme dilutions used in homeopathic preparations usually leave none of the original substance in the final product.
A number of speculative mechanisms have been advanced to counter this, the most widely discussed being water memory, though this is now considered erroneous since short-range order in water only persists for about 1 picosecond. No evidence of stable clusters of water molecules was found when homeopathic preparations were studied using nuclear magnetic resonance, and many other physical experiments in homeopathy have been found to be of low methodological quality, which precludes any meaningful conclusion. Existence of a pharmacological effect in the absence of any true active ingredient is inconsistent with the law of mass action and the observed dose-response relationships characteristic of therapeutic drugs (whereas placebo effects are non-specific and unrelated to pharmacological activity).
Homeopaths contend that their methods produce a therapeutically active preparation, selectively including only the intended substance, though critics note that any water will have been in contact with millions of different substances throughout its history, and homeopaths have not been able to account for a reason why only the selected homeopathic substance would be a special case in their process. For comparison, ISO 3696:1987 defines a standard for water used in laboratory analysis; this allows for a contaminant level of ten parts per billion, 4C in homeopathic notation. This water may not be kept in glass as contaminants will leach out into the water.
Practitioners of homeopathy hold that higher dilutions―described as being of higher "potency"―produce stronger medicinal effects. This idea is also inconsistent with observed dose-response relationships, where effects are dependent on the concentration of the active ingredient in the body. This dose-response relationship has been confirmed in myriad experiments on organisms as diverse as nematodes, rats, and humans. Some homeopaths contend that the phenomenon of hormesis may support the idea of dilution increasing potency, but the dose-response relationship outside the zone of hormesis declines with dilution as normal, and nonlinear pharmacological effects do not provide any credible support for homeopathy.
Physicist Robert L. Park, former executive director of the American Physical Society, is quoted as saying,
"since the least amount of a substance in a solution is one molecule, a 30C solution would have to have at least one molecule of the original substance dissolved in a minimum of 1,000,000,000,000,000,000,000,000,000,000,