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Homeopathy or homoeopathy is a system of alternative medicine. The term derives from the Greek hómoios (similar) and páthos (suffering). The underlying concept of homeopathy is "like cures like" and is based on "the principle of similars", which asserts that substances known to cause particular symptoms can also, in low and specially prepared doses, help to cure diseases that cause similar symptoms. Most mainstream medical doctors and scientists, particularly those in the West, do not accept the principles of homeopathy today because of the lack of plausability for its premise that the remedies maintain a healing quality even when they are diluted to the point of no molecular content. Since they do not believe the remedies have therapeutic effect, they consider homeopathy dangerous because its use may delay potentially lifesaving conventional treatments, especially in emergencies such as severe asthma.

Some principles of homeopathy have been utilized in various forms in various medical systems for thouands of years in many diverse cultures, but they were first methodically set out by a German physician, Samuel Hahnemann (1755–1843), who observed that a medicine sometimes evoked symptoms similar to those of the illness for which it was prescribed. Related maxims such as the "Law of similars" are common in anthropological literature, and also are called sympathetic magic.

In homeopathic theory, every person has a "vital force", with the power to promote healing and/or maintain good health (the term "vital force" is akin to qi in traditional Chinese medicine). In this theory, the symptoms of a disease reflect efforts of the vital force to counter infection, or to resist damage from environmental toxins or from various stresses. Homeopathic treatment attempts to strengthen this "vital force" with the help of remedies, which are extremely small doses of drugs diluted and vigorously shaken ("succussed") in water or ethanol and dispensed in pills or liquid form. They are chosen for their ability (in large doses) to provoke the very symptoms that the remedy is intended to heal (and thereby for their presumed ability to stimulate natural healing). Homeopaths believe that this "vital force" is akin to what physiologists would call the body's "defense systems".

Although homeopathy is practiced by some medical doctors, as well as by other health professionals in virtually every country in the world, it is generally regarded as ineffective although its remedies may be nontoxic. In addition to those homeopathic remedies prescribed in the professions practicing homeopathy, remedies are used by consumers all over the world for self-treatment of common self-limiting ailments and injuries.

"Classical homeopathy" or "Hahnemannian homeopathy" refers to the original principles of this medical system in which a single remedy is chosen according to the physical, emotional, and mental symptoms that the sick individual is experiencing rather than only the diagnosis of a disease. "Commercial" or "user-friendly" homeopathy refers to the use of a mixture of remedies in a single formula containing individual ingredients that are generally chosen by the manufacturer for treating specific ailments.

Overview

As stated, many natural scientists and medical doctors doubt that homeopathic healing methods have any efficacy. They regard the evidence that is cited in support of efficacy as extremely weak, while pointing out that implausible claims need extraordinary proofs. In response, homeopaths assert that, in their view, the overall evidence for homeopathy, including clinical research, animal research, basic sciences research, historical usage of homeopathic medicines in the treatment of people in various infectious disease epidemics, and widespread and international usage of homeopathic medicines today, indeed provide extraordinary evidence for the benefits of this system.

It is without doubt that homeopathy has a rich history; many famous people over the past 200 years have been users and advocates of it , and it is an important element in the history of medicine generally. The growth of homeopathy in the 19th century had a significant influence in determining how conventional medicine organised and developed, and in how it came to formulate its present vision of evidence-based medicine, in contrast to practice based on individual clinical experience.

Homeopaths are proud of their history, and are convinced of the efficacy of their remedies based mainly on their clinical experience, bolstered by the outcomes of the majority of their clinical trials. Homeopathic remedies are used by many people throughout the world; like many other complementary and alternative therapies, homeopathy generally scores highly in "patient satisfaction" surveys, and it has a reservoir of public support. In the U.K. for instance, one of the countries where homeopathy has relatively strong public support, a survey cited by the British Homeopathic Association found that 15% of the public "trust" homeopathy.

Scientists and medical professionals are also often interested in homeopathy. They are interested in why so many people believe in homeopathy, when they consider that it has no plausibility. They are interested too in why some studies appear to have positive outcomes—do these reflect real efficacy, or can they be accounted for by flaws in study design or in statistical analysis, or "publication bias"—the tendency for small studies with chance positive outcomes to be published while studies with negative or inconclusive outcomes are not. They also are interested in whether positive results against expectation sometimes reflect manipulation of data or perhaps even fraud.

Historical origins

The early Greek physician Hippocrates of Cos (c. 450 BCE - 380 BCE) , who is considered to be the "father of medicine", is also claimed by homeopaths as a pioneer in their own tradition—notably because Hippocrates taught that "Natural forces within us are the true healers of disease," but also because he thought that some diseases could be cured by the same things that caused them—arguably an early expression of the principle of similars. In the 15th century the alchemist, physician, and astrologer Paracelsus proposed the healing power of "signatures", by which he meant that the appearance of a substance in nature (its color and its shape) represented the types of diseases that it could cure. It was not until the late 18th century, however, that this theory was coupled with an experimental method to determine in detail what symptoms a substance causes and thereby what a particular medicine might cure. This experimental method was developed by the German physician Samuel Hahnemann with his method of "provings"—studies of the effects, in humans, of high dosages.

In 1783, disillusioned with the medicine of his time and the many toxic effects of its treatments, Hahnemann, who knew nine languages, gave up his medical practice and devoted himself to translating medical books, including many of the leading textbooks of the day. Among them was the Treatise on Materia Medica (1789) by William Cullen, the leading physician of the 18th century. Cullen had written that cinchona bark (which contains quinine) was effective in treating malaria because of its bitter and astringent properties. Hahnemann questioned this theory because he knew that other substances were as bitter and astringent, but had no therapeutic value in this deadly disease.

Being an avid experimenter, Hahnemann took cinchona bark himself and saw that the symptoms that it caused were similar to the symptoms of the diseases for which it was prescribed. He then experimented with other substances and found that the symptoms that they caused were also similar to the symptoms of the diseases for which they were prescribed. These experiments led him to formulate the "principle of similars" - similia similibus curentur or "let likes cure likes". He used his experiments and the principle of similars to develop a new system of health care, as an alternative to the often toxic and ineffective drugs and treatments offered by conventional physicians of the time.

Hahnemann named his system of health care "homeopathy" (meaning "like disease") and coined the term "allopathy" ("different than disease") to refer to the conventional medicine of the day, because its drugs were sometimes "similar," sometimes "opposite," but usually just "different" to the symptoms of the sick person.

For the first two decades of Hahnemann's practice of homeopathy, he used "crude" doses of various medicinal substances ("crude", in homeopathic use, means doses that still contain some of the original ingredient). He strove to find the lowest doses at which his remedies would still be effective, as he thought this the best way to avoid any adverse side-effects. To his surprise, it seemed that reducing the dose did not reduce the effectiveness of his treatments. Instead, he concluded that his remedies worked better the more he diluted them as long as he “potentized” them between each stage of dilution by vigorous shaking (succussion). Homeopathy thus became inextricably linked with this process of ultradilution—repeated dilution of substances by succussion. Hahnemann did not offer a clear explanation as to how or why these potentized medicines might have therapeutic benefits; he distrusted all theoretical explanations and argued that all that mattered was whether a treatment was therapeutically effective.. He believed that diseases were caused by "spirit-like derangements of the spirit-like power that animates the human body" and that effective healing called for medicines that would stimulate this life force.

Homeopathy was introduced into the U.S.A. in 1825 by Hans Burch Gram, a Boston-born doctor who had studied homeopathy in Europe. In 1830 the first homeopathic schools opened (the first homeopathic medical college in the U.S.A. opened in 1835, in Allentown, Pennsylvania), and throughout the 19th century dozens of homeopathic institutions appeared in Europe and the U.S.A. Apart from his ventures into homeopathy, Hahnemann had been a prominent and respected public health reformer, and in the 1830s the Medical Society of the Country of New York had granted him honorary membership. However, a few years later the society rescinded this when they realized the "ideological and financial threat" that homeopathic medicine posed. In 1844, the first U.S. national medical association - the American Institute of Homoeopathy - was established. By the end of the 19th century, 8% of American medical practitioners were homeopaths, and there were 20 homeopathic medical colleges (including Boston University, New York Medical College, and the Universities of Ohio State, Iowa, Minnesota and Michigan) and more than 100 homeopathic hospitals in the U.S.A. One reason for the growing popularity of homeopathy was its relative success in treating people suffering from the infectious disease epidemics that raged at the time. Cholera, scarlet fever, typhoid fever, and yellow fever were rampant and killed many people, but death rates in homeopathic hospitals were often very much lower than in the conventional hospitals, whose cures – purging, blood-letting and mercury treatments, were often worse than the diseases, and did nothing to combat them.

In the early 20th century, the "Flexner Report," sponsored by the Carnegie Foundation with support from the American Medical Association, triggered major changes in American medical education. As a result, most homeopathic schools were closed down, while others became conventional medical schools (including Boston University, New York Medical College, and Ohio State University). In the 1960s, the popularity of homeopathy began to revive again in the U.S.A, and a 1999 survey reported that over 6 million Americans had used homeopathy in the previous 12 months.

Homeopathic "provings"

Homeopathic practitioners determine the specific therapeutic indications for their remedies from experiments in toxicology called provings, in which volunteers are given repeated doses of substances (usually in single-blind or double-blind trials), until symptoms of overdose are observed. The effects of each medicinal substance are recorded in textbooks, called Materia Medica and Repertory, or nowadays in expert system software. Homeopathic provings provide an experimental basis to determine what a substance causes in overdose and thereby what it is thought to cure. The symptom complexes that these substances cause are subsequently used to compare with a patient's physical and psychological symptoms in order to select, as the appropriate most similar remedy, the substance whose effects are closest to the patient's symptoms—called the "simillimum".

An example of a proving is that of Bambusa arundinacea (bamboo). In this proving, the 20 subjects did not know whether they were taking the bamboo or a placebo, and the investigator knew only the substance name, but not, at that time, its properties. The 6C and 30C potencies were used, and the investigators found that the central idea of this new remedy is the “search for support”. The symptoms elicited by the treatments are detailed in a 237-page book, which details the hundreds of symptoms that bamboo was found to cause (and therefore, according to homeopathic principles, potentized doses of this medicine will stimulate to heal people whose symptoms are similar to this syndrome of symptoms).

In the first two phases of the proving, all of the subjects were given the remedy in various potencies. In the third phase, seven of them were given placebo. Those given placebo experienced similar symptoms; the author attributed these to the fact that the placebo and the remedy had been only separated by a thin layer of the paper bag while in transit, leading, he suggested, to a "copying of the dynamized information of the homeopathic remedy onto the undynamized 'placebo'" The study started in October 1994 and lasted until February 1995, during which time they recorded every symptom they experienced in a diary and noted whether it was a persistent, new, old, altered or unusual symptom. The recorded symptoms take up 84 pages in the book. The symptoms are then converted into repertory rubrics in the next 46 pages. The last 76 pages consist of the author's commentary about the proving symptoms, and 14 cases in which bamboo was the prescribed remedy.

Homeopaths prescribe this remedy (in potentized doses) when a sick person has a syndrome of symptoms that resemble the syndrome of symptoms that it causes in drug proving. The recorded symptoms need to be interpreted by an experienced homeopath to understand the conditions for which the remedy might be considered as possibly useful. In the case of bamboo, some homeopaths have determined that one of the themes of people who will benefit from this medicine is a "search for support." The proving cites that this remedy is also useful in treating post-natal depression accompanied by irritability and impatience, for example when a mother makes statements like "I can't handle my child and I have no desire to get out of bed." In cases requiring physical support, it is indicated when there is a need for support in the back associated with pain, sciatica, stiffness and changes to the spine. Finally it is indicated with symptoms such as swelling of the breasts before menses accompanying depression.

In September 2006 the U.K.’s licensing body, the Medicine and Healthcare Products Regulatory Agency, altered their regulations to permit homeopathic remedies to be advertised using homeopathic provings to support their claims (justifying phrasing such as “For the relief of...”. This change elicited protests from scientists, who called it a departure from the principle that such claims should be justified by evidence of efficacy.

Homeopathic manufacture of remedies

In the U.S.A., the Homœopathic Pharmacopœia of the United States is a legally recognized handbook that describes how to manufacture homeopathic drugs. This reference is approved by the Food and Drug Administration (FDA), the governmental agency that regulates drugs. Medicines listed in the HPUS defines them as homeopathic drugs which grants them a different standard of drug regulation than conventional drugs and medical devices. A summary describes the principles:

FDA regulates homeopathic drugs in several significantly different ways from other drugs. The Manufacturers of homeopathic drugs are deferred from submitting new drug applications to FDA. Their products are exempt from good manufacturing practice requirements related to expiration dating and from finished product testing for identity and strength. Homeopathic drugs in solid oral dosage form must have an imprint that identifies the manufacturer and which indicates that the drug is homeopathic.

In 1938, the federal Food, Drug, and Cosmetic Act, sponsored by New York Senator Royal Copeland, a homeopathic physician (and former homeopathic medical school dean), gave the FDA the power to regulate drugs and granted legal recognition to the "Homeopathic Pharmacopeia of the United States" as a compendium of drugs. In contrast, non-homeopathic drugs for which a New Drug Application is required must be accompanied by approved evidence of safety and efficacy; simple listing in a reference is not sufficient. Today, homeopaths use about 3,000 different remedies, from animal, plant, mineral, or synthetic sources.

By convention, the first letter of the Latin-derived name of such preparations is capitalized. When the source is well-defined, the traditional name rather than chemical, International Nonproprietary Name or biological nomenclature, is preferred, such as Natrum muriaticum rather than sodium chloride. Ultimately, any substance can become a homeopathic medicine if "drug provings" (tests to determine the symptoms produced by toxic doses) are first conducted to determine what it causes in overdose and therefore what it can cure in potentized doses. Remedies used in homeopathy are commonly made from plants, trees, fungi, and algae, as well as from a wide variety of mineral and animal sources. Even some unusual substances, called imponderables, can and are made into homeopathic medicines, including electricity, X-ray, and magnetic north and south poles.

Homeopathic remedies are available in several different forms (single medicine, homeopathic formula or complex medicines, and a limited number of external applications). Remedies for internal consumption come either in pill form or as liquid. Most do not require a doctor's prescription, but some may need one if the dosage is in a non-potentized or low potency dose and if the substance is potentially toxic (in Europe, a medicine must be diluted at least 1:10 three times to be deemed homeopathic). In the U.S.A., if a homeopathic remedy is claimed to treat a serious disease such as cancer, it can be sold only by prescription. Only products sold for “self-limiting conditions”—colds, coughs, fever, headaches, and other minor health problems that are expected to go away on their own—can be sold without a prescription (over-the-counter).

Preparation of homeopathic remedies

The most characteristic — and controversial — principle of homeopathy is that the efficacy of a remedy can be enhanced and its side-effects reduced by a process known as "dynamization" or "potentization". In this process, liquids are diluted (with water or ethanol) and shaken by ten hard strikes against an elastic body ("succussion"), to get the next, succeeding higher potency. For this, Hahnemann had a saddlemaker construct a wooden "striking board", covered in leather on one side and stuffed with horsehair. When insoluble solids such as oyster shell are used for remedies, they are diluted by grinding them with lactose ("trituration"). The original serial dilutions by Hahnemann used a 1 part in 100 (centesimal; "C" potencies), or 1 part in 50,000 (quintamillesimal; "LM" or "L" potencies). Dr. Constantine Hering of Philadelphia later introduced the Decimal potencies ("D" or "X" potencies). A large number of homeopathic medicines sold in health food stores and pharmacies are "low potencies," that is, doses that are 3X, 3C, 6X, 6C, 12X, and 12C, all of which, except the last dose, have material doses of the original substances in the medicine. The higher potencies (30, 200, 1,000 and higher) are more commonly prescribed by professional homeopaths, and typically homeopaths have found these doses to be powerful enough to only need a single dose to have a long-term effect (from several weeks to several months or longer). Research studies that determine the efficacy of homeopathic medicines are discussed elsewhere in this article.

The dilution factor at each stage is 1:100 ("C" potencies), 1:50,000 ("LM" potencies) or 1:10 ("D" or "X" potencies) ; Hahnemann advocated $30C$ dilutions for most purposes (i.e. dilution by a factor of 100³⁰ = 10⁶⁰). The number of molecules in a given weight of a substance can be calculated by Avogadro's number (see the section "Attempts to provide a scientific foundation for homeopathy" below), and it is extremely unlikely that even one molecule of the original substance would be present in a $30C$ dilution. Thus, homeopathic remedies of a high "potency"' contain just water, but according to homeopaths, the structure of the water has been altered (see memory of water).

"Classical homeopathy" or "Hahnemannian homeopathy" refers to the original principles of this medical system in which a single remedy is chosen according to the physical, emotional, and mental symptoms that the sick individual is experiencing rather than only the diagnosis of a disease. "Commercial" or "user-friendly" homeopathy refers to the use of a mixture of remedies in a single formula containing individual ingredients that are generally chosen by the manufacturer for treating specific ailments. Such homeopathic remedies are used by consumers all over the world for self-treatment of common self-limiting ailments and injuries.

Similia similibus curentur : the law of similars

Similia similibus curentur or "let likes cure likes", is the assertion that a disease/problem can be cured by remedies that (in macroscopic, milligram doses) produce the same symptoms as those of the disease. This assertion, known as "the law of similars", is a guiding principle in homeopathy. Homeopaths consider that two conventional concepts, vaccination, and hormesis, can be considered as analagous to homeopathy's law of similars and the use of small doses.

Scientists and medical doctors today do not think that the principle of similars is generally true or useful, and they explain the efficacy of vaccination without referrring to it. Physicians of the 19th century however did consider that the principle could be valuable. For example, Emil Adolph von Behring (1854-1917), who won the first Nobel Prize in medicine in 1901 for discoveries that led to vaccines against tetanus and diphtheria, and who some consider to be the father of immunology, asserted that vaccination is, in part, derived from the homeopathic principle of similars.

In spite of all scientific speculations and experiments regarding smallpox vaccination, Jenner’s discovery remained an erratic blocking medicine, till the biochemically thinking Pasteur, devoid of all medical classroom knowledge, traced the origin of this therapeutic block to a principle which cannot better be characterized than by Hahnemann’s word: homeopathic.

Although homeopathic remedies and vaccinations both use low doses of active ingedients, there are important differences. First, the doses used in homeopathic remedies are always very much lower than used in vaccines. Second, vaccines produce a measurable immune response (e.g., immunoglobulin production). Homeopathic remedies do not routinely produce a measurable immune response. Thus conventional treatments involve application of measurable doses of substances, at levels known to activate a cellular response. In contrast, homeopathic preparations above the $24X$ ($12C$) potencies do not contain enough molecules to activate any known metabolic or signalling pathway.

Mithridatization (which is not a term used in contemporary science or medicine) may be a better metaphor than vaccination for homeopathic treatment. Mithridatization is the chronic administration of subtoxic doses of a toxin, in an attempt to develop resistance (or "tolerance") to large doses of the toxin. It is said that Mithridates VI Eupator, King of Pontus (132-63 BC), used this technique to protect himself from his enemies.

There are many different mechanisms by which tolerance can develop - and exposure to repeated small doses does not always result in tolerance. A herpetologist who receives many small doses of snake venom may indeed become tolerant to them. A beekeeper, however, may become hypersensitive to the venom and, after receiving a sting, go into anaphylaxis. This type of response to small, not necessarily precisely measured, doses is not predictable on an individual basis. "Allergic desensitization" is a technique used in conventional medicine to treat individuals who have a specific allergy to something that they cannot easily avoid. This involves exposing the patient repeatedly to tightly controlled doses, increasing the doses gradually over time. This treatment can be dangerous (exposure of sensitive individuals to an allergen can produce anaphylaxis), and it has very inconsistent efficacy, so is normally only attempted when the allergy poses serious restrictions on the patient's normal life.

Both mithridatization and homeopathy might be considered as instances of hormesis, which describes the phenomenon that some chemicals at high concentrations have opposite biological effects to those at low concentrations.

Professional homeopaths: who are they?

There are no universal standards for homeopathic education, so licensing and regulation varies from country to country and from state to state within the U.S.A. In some countries, all (or virtually all) professionals that use homeopathic treatments are MDs (such as France, Spain, Argentina, Colombia). Some countries have exclusively homeopathic medical schools (India, Pakistan, Mexico etc.), some have naturopathic medicine colleges in which students are taught homeopathy as part of their curriculum (Germany has its "heilpraktica"/health practitioners; the U.S.A., Canada, and Australia have naturopathic medicine schools that include homeopathy), and some countries certify "professional homeopaths" who have attended homeopathic schools and who then pass independent examinations that grant "certification" as homeopaths. In the U.S.A., there is also a separate certification process available only to MDs and DOs (there are similar choices of certification available in the U.K. for medical doctors, who've done at least MBBS). Also in the U.S.A., naturopathic physicians have their own homeopathic certifying agency.

In Europe homeopathy is practiced by many conventional physicians, including 30-40% of French doctors and 20% of German doctors. Some homeopathic treatment is partly covered by some European public health services, including in France and Denmark. In the U.K., five homeopathic hospitals are funded by the National Health Service (NHS) and homeopathic remedies are sold over the counter, and there, homeopathy is one of the most popular alternative and complementary treatment modalities . Of 248,000 registered practitioners of medicine in the U.K., about 400 are members of the Faculty of Homeopathy. However, homeopathy is still not a fully regulated profession in the U.K.—anyone can declare themselves to be a homeopath and practice without any qualification ("common law" that allows freedom of choice in medical care in England has a long history)

In France and Denmark licenses are required to diagnose any illness or to dispense any product whose purpose is to treat illness. In many countries, however, there are no specific legal regulations concerning homeopathy. In Austria, the public health service generally requires proof of effectiveness to reimburse medical treatments, but makes an exception for homeopathy.

In India, where there are more than 200,000 registered practitioners of homeopathy, homeopathy is formally recognised by the Government as one of the Indian "National Systems of Medicine", under the Department of AYUSH (Ayurveda, Yoga and Naturopathy, Unani, Siddha and Homeopathy), while conventional, western medical education is controlled by the Medical Council of India. About 10% of the Indian population depends solely on homeopathy for their health care needs. In India it is illegal to practice as a homeopath without a license and professional qualifications.

Almost 70% of all over-the-counter homeopathic remedies are sold in Western Europe. France is the largest market for homeopathic remedies in the world, worth over 300 million euros in 2003 (in a total over-the-counter drug market of over 770 billion euros), followed by Germany (200 million euros). The global self-medication market is estimated at 48.2 billion dollars (13.4% of the world pharmaceuticals market), of which sales of homeopathic remedies account for 0.3%.

A typical homeopathic visit

When a homeopath is conducting an interview to characterise a patient's syndrome of symptoms, some "categories of change" are identified as important: (1) emotion (2) mentation (3) specific physical functioning (4) general physical changes (5) perception of self (6) relationships (7) spirituality (8) lifestyle (9) energy (10) dream content and tone (11) well-being (12) perceptions by others (13) life relationships (14) a sense of freedom or feeling less "stuck" (15) sleep (16) coping (17) ability to adapt (18) creativity (19) recall of past experiences

Homeopathic remedies can be prescribed by professional homeopaths, naturopaths, acupuncturists, chiropractors, and physicians with additional homeopathic training and certification, and how these decide what to prescribe will differ accordingly. Classical homeopaths place emphasis on the patient's unique symptoms and their psychological state, and they gather this information from an interview, typically lasting from 15 minutes to two hours (comparable to conventional physicians), with one or more follow-up consultations of 15 to 45 minutes. They place special emphasis on the way the patient experiences their disease—i.e. they give priority to the overall syndrome of symptoms and the unique and idiosyncratic symptoms which they consider different than the conventional medical approach of trying to identify the causes of the disease. The goal is to determine the factors that might predispose the patient to disease and find a treatment that will strengthen that particular patient's "overall constitution".

After the interview, the homeopath consults the references described in the table on the right. Some homeopaths make quick prescriptions based on "keynotes"—the highlights of the best known characteristics of a remedy, but the real challenge of homeopathic practice is to find the remedy that best matches the patient's syndrome of physical and psychological symptoms—the "similimum". A fundamental reason for conflict between conventional medicine and homeopathy is that homeopathy rejects the concept of treatments that target mechanisms of disease, and instead uses remedies that target syndromes of symptoms that they believe strengthen a person's overall constitution. Some homeopathic protocols might look like the following:

• A physician qualified in both homeopathy and conventional medicine, after diagnosing a chronic condition that does not indicate the need for medical urgency, will usually first prescribe a homeopathic remedy which he feels may be more effective and is likely to have fewer side effects than conventional drugs.
• Homeopaths recognize that trauma might require conventional medical attention but may complement the conventional treatment with homeopathy.
• Homeopaths disagree with conventional medicine about the role of immunization and chemoprophylaxis for infectious diseases and prefer to prescribe homeopathic remedies that they believe will strengthen a person's immune and defense system.
• For some disease conditions, such as asthma and acute bronchitis, homeopathic remedies are often prescribed not only to alleviate chronic symptoms, but also to treat acute attacks. Homeopathic remedies might also be used after an asthmatic episode with the intent to prevent recurrences.
• An adequately trained homeopath is expected to recognize symptoms that indicate an acute and potentially fatal condition. The practitioner is expected to have emergency medical training and equipment appropriate to his or her level of training in the place of practice (e.g., dressings and basic airway management tools for an individual with training at the Emergency Medical Technician (EMT) of Basic or higher level, and preferably an automatic external defibrillator and advanced cardiac life support resources generally accepted as appropriate for an office. Potentially serious acute ailments may require medical supervision, but homeopaths sometimes prescribe remedies either for adjunctive use or as alternatives to conventional treatment.

The homeopathic treatment of acute injuries does not need the same depth or breadth of interview as treatment of chronic conditions. According to homeopaths, because the symptoms of a common cold or a headache or an allergy vary from person to person, each may need a different remedy. However, they believe that people who experience an injury generally have similar symptoms, so they think that some homeopathic remedies might be routinely useful in such cases.

Homeopaths who practice "classical homeopathy" prescribe just one remedy at a time—a remedy that best fits the overall syndrome of the patient. The same remedy might thus be prescribed for patients suffering from very different diseases; conversely, patients suffering from what would be diagnosed conventionally as the same disease may be prescribed different remedies. For example, hay fever would be treated with any of several remedies, usually based on the specific symptoms, but sometimes on the etiology of the allergy. Some common remedies are: Allium cepa (onion, which causes tears to flow and a clear burning nasal discharge that irritates the nostrils), Euphrasia (eyebright, which causes a clear and bland nasal discharge along with tears that burn and irritate the skin under the eye), Ambrosia (ragweed) and Solidago (goldenrod); ,ragweed and goldenrod are herbs whose pollen is aggravating to some hay fever sufferers. These remedies are commonly given during the acute symptoms of hay fever. At other times, a professional homeopath will often treat these patients with a constitutional remedy based on the patient’s genetic history, health history, and present overall physical and psychological state, with the intent to strengthen the person’s general health, thereby reducing the frequency or intensity of the symptoms of hay fever.

The claims for homeopathy

Homeopaths view illness as a systemic condition, a disturbance in the overall homeostasis of the total being and accordingly, consider that almost any sick person, may benefit from proper homeopathic treatment. As the American Institute of Homeopathy puts it in their "Standards of Practice": "The physician must remember that he is treating a patient who has some disorder; he is not prescribing for a disease entity." .

Homeopathic practitioners claim that their remedies are useful for a wide range of minor ailments, from cuts and bruises to coughs and colds. Patients often come to homeopaths with long-term problems which have not responded to conventional medicine, and homeopaths prescribe remedies to people with these conditions. Some of the common ailments for which patients seek homeopathic care are eczema, chronic fatigue syndrome, asthma, migraine, irritable bowel syndrome, allergic disorders, arthritis, fibromyalgia, hypertension, Crohn's disease, premenstrual syndrome, rhinitis, anxiety and depression. They also treat patients with the most serious diseases, including multiple sclerosis, chronic obstructive pulmonary disease, and cancer. and AIDS For gangrene, for example, homeopathic remedies are prescribed in the belief that they will strengthen a person's own defenses and to initiate healing. Some homeopathic remedies for gangrene include Arsenicum Album, Secale (from rye/ergot), and Carbo vegetabilis (from charcoal), amongst many others.

Homeopaths claim that there is objective evidence that some of their treatments are beneficial (see Tests of the efficacy of homeopathy), and they believe that the success of homeopathy for the last 200 years is itself an indication of its value.

Conflict with conventional medicine

James Tyler Kent and homeoprophylaxis Some homeopaths also believe that their treatments can prevent disease, a notion known as "'homeoprophylaxis". James Tyler Kent (1849-1916) was prominently associated with the spread of homeopathy in the U.S.A., and much modern practice of homeopathy is based on his repertory, published in 1897. Kent denied the conventional germ theory of infectious disease, declaring that "The microbe is not the cause of disease. We should not be carried away by these idle allopathic dreams and vain imaginations but should correct the Élan vital". Instead, he believed that illness had spiritual causes: "You cannot divorce medicine and theology. Man exists all the way down from his innermost spiritual, to his outermost natural." Kent promoted the idea that homeopathic remedies could not only cure diseases, but also prevent them: "The great prophylactic is the homeopathic remedy. After working in an epidemic for a few weeks, you will find perhaps that half a dozen remedies are daily indicated and one in these remedies in a larger number of cases than any other. This one remedy seems to be the best suited to the general nature of the sickness. Now you will find that for prophylaxis there is required a less degree of similitude than is necessary for curing. A remedy will not have to be so similar to prevent disease as to cure it, and these remedies in daily use will enable you to prevent a large number of people from becoming sick. We must look to homeopathy for our protection as well as for our cure". The notion of homeoprophylaxis has not received support from systematic trials and has no place in conventional medicine. Suggestions that homeopathic treatments are an effective alternative to vaccination are regarded as irresponsible by many public health professionals, and also by some professional homeopathic organizations; in the U.K., The Faculty for Homeopathy recognizes the importance of childhood vaccination and does not support the common use of homeopathic remedies in place of conventional travel vaccinations and for malaria prevention, warning travellers "that there is no evidence that these provide any degree of protection." In 2007, the Ministry of Health in Cuba gave 2.4 million people two doses of a leptospira nosode as homeoprophylaxis against an expected outbreak of leptospirosis (a bacterial infection spread by rats, or by contaminated water) after unusually heavy rainfall. According to a report at a conference on homeoprophylaxis was held in Cuba in late 2008, sponsored by the Finlay Institute, the Cuban manufacturer of the nosode, the levels of subsequent morbidity were below those expected given the rainfall and season.

The theory underlying homeopathy is not considered plausible by most scientists working in academic institutions in Europe and the U.S.A., and in key respects, the treatment advice offered by homeopaths is in disagreement with conventional medicine.

The conventional view is that homeopathy, insofar as it has any effect at all, exploits the placebo effect - i.e. that the only benefits are those induced by the power of suggestion, by arousing hope, and by alleviating anxiety. Conventional medical opinion does not deny the efficacy of placebo treatments in many cases, and placebos have played a large part in conventional medicine since their first deliberate use by William Cullen in the 18th century. Many modern physicians, however, consider it unethical to deliberately mislead their patients; rather than prescribing placebos themselves, some therefore prefer to refer patients to regulated practitioners of alternative medicine.

Some homeopaths, especially with medical training, will use conventional techniques to treat asthmatic and other respiratory medicine, but will use homeopathic methods for long-term care. One of the challenges here is that the standard of medical therapy for asthma is to prevent inflammation, which commonly involves inhaled corticosteroids that are not absorbed beyond the respiratory system.

Homeopaths also assert that corticosteroids are immunosuppressant drugs that only provide temporary relief of asthma symptoms and may lead to more serious chronic disease and to increased chances of death. Medical opinion is that this assertion is uninformed scare-mongering. They advise that corticosteroids prevent inflammation that can have serious consequences and symptom relief is a result of this anti-inflammatory action. Inhaled corticosteroids that stay on the breathing passages and do not spread through the body are medically preferred to systemic corticosteroid therapy and thus reduce immune suppressing effects of these drugs.

Most homeopaths believe that the fundamental causes of disease are internal and constitutional and that infectious disease is not just the result of infection but also of susceptibility. This viewpoint leads them to seek to avoid conventional treatments that suppress symptoms. physicians accept that some disease is indeed a disturbance in normal function, whether due to external, genetic, or internal reasons. However, they consider that most disease can be attributed to a combination of external causes (such as viruses, bacteria, toxins, dietary deficiency, physical injury) and physiological dysfunction (including genetic defects and mutations such as those which trigger cancers), some of which are more than the healthy body can resist. Homeopaths consider them to be co-factors to disease, not causes of them. Conventional physicians acknowledge that they often use drugs simply to suppress the symptoms of a disease (to alleviate the pain, injury, and distress that they cause), but they maintain that their main goal of medical treatment is to eliminate the causes of the disease with the help of drugs.

Whereas homeopaths emphasize that they provide remedies tailored to the individual patient's symptoms, conventional medicine focuses on treatments with demonstrable efficacy when given in a standard form to large populations of patients with a given disease. However, large clinical trials also seek to identify subgroups of patients (identifiable by age, gender, ethnicity, lifestyle, comorbidities etc.) that are "responders" or "non responders" to a new treatment, to provide a rational basis for individualization of treatments. Conventional physicians have access to a very large repertoire of prescription drugs for this purpose (11,706 in the U.S. Food and Drug Administration Approved Drug Products with Therapeutic Equivalence Evaluations 26th Edition Electronic Orange Book (EOB)4 ) , a repertoire that is constantly changing as less effective drugs are replaced by better drugs.

Medical organizations' attitudes towards homeopathy

The American Medical Association (AMA) was founded in 1847, three years after the American Institute of Homeopathy. From the 1860s to the early 20th century, the AMA's ethical code forbade its members to consult with fellow MDs who practiced homeopathy. Although the AMA did not enforce many of its ethical guidelines, the "consultation clause" was one of the few that it did. Today, the AMA is no longer overtly antagonistic to homeopathy, but their current policy statement says: "There is little evidence to confirm the safety or efficacy of most alternative therapies. Much of the information currently known about these therapies makes it clear that many have not been shown to be efficacious."

Safety and efficacy of homeopathy

In conventional medicine (see New Drug Application), the basic phases of evaluating a drug are determining if it causes dangerous effects in healthy volunteers, if it is adequately present in the body to achieve an effect, and if it is more effective than established treatments, against a disease.

In conventional medicine, randomized controlled trials rely on statistical analysis of large groups of patients all of whom are given the same treatment to determine whether that treatment is indeed effective. This conflicts with an approach that believes that treatments must be individually tailored to each patient. In reality, some homeopathic trials do use some standardization, but not always to an extent which would make the trials statistically robust.

Few people question the safety issues in choosing homeopathic medicines themselves, and the U.S. F.D.A. determines what dose is basically safe for over-the-counter sales of homeopathic medicines. However, homeopaths discourage the general public from using the homeopathic high potency medicines (the 200th potency and higher potencies) unless the person is adequately trained in homeopathy. Homeopaths warn the public that repeated doses of high potency medicines can lead the person to experience a "drug proving," a situation in which the person experiences symptoms akin to an overdose of the substance (the symptoms are generally known to resolve themselves shortly after the person stops taking the medicine).

Attempts to provide a scientific foundation for homeopathy

Homeopathy was developed at a time when many important concepts of modern chemistry and biology, such as molecules and germs, were understood poorly if at all. In Hahnemann's day, many chemists believed that matter was infinitely divisible, so that it was meaningful to talk about dilution to any degree. Although the hypothesis of atoms can be traced back to the ancient Greeks, their size was not calculated until 1865 (by Josef Loschmidt).

We now know that, for example, a teaspoon of seawater (roughly 5 ml) contains about 160 mg of NaCl. The molecular weight of NaCl is 58.4, so by Avogadro's number, (or, in German-speaking countries, Loschmidt's number), 58.4 g of NaCl (one mole) contains 6.02×10²³ molecules. We can thus calculate that our teaspoon contains about 2×10²¹ molecules of NaCl. A 12C dilution of seawater will have about one molecule of NaCl per litre.

Thus homeopathic remedies diluted to more than about 12C are virtually certain to contain not even a single molecule of the initial substance. This is recognized by advocates of homeopathy, who assert that the essential healing power is not to be found in the chemical action of molecules, but perhaps in the arrangement of the water molecules, giving rise to the expression "the memory of water". In the homeopathic literature widely differing explanations are proposed for the alleged existence of this water memory. It appears that the community of homeopaths has not yet converged on a single explanatory paradigm.

For instance, homeopaths like to point out that water is not simply a collection of molecules of H₂O, but contain isotopologues, molecules with different isotopic compositions such as HDO, D₂O and H₂¹⁸O. Mass spectroscopy can indeed detect different isotopologues, but their relative concentration is the same before and after homeopathic treatment—the concentration ratios can only be changed by nuclear reactions—so that the presence of isotopologues in water cannot explain its memory.

Also the fact that the molecules H₂O appear in two proton-spin forms (ortho and para) has been suggested as a source of memory of water. These two spin forms, which appear in a ratio 3:1, are chemically non-distinguishable and are very difficult to separate or to convert into each other. It is therefore highly unlikely that a homeopathic treatment could change this ratio. Moreover, even if it is assumed that homeopathic tinctures would give somehow rise to ortho:para ratios other than 3:1, it requires much further explanation that these (chemically undetectable) ratios have different healing qualities.

Another suggestion is that double-distilled and deionized water contains trace amounts of contaminating ions. In particular, water, as a result of repeated vigorous shaking, might include dissolved atmospheric gases in the form of nanobubbles, molecular ions produced from water reacting with airborne contaminants, and silicates—tiny glass "chips". These possibilities are discussed in Ref. and Ref. But see for further discussion Ref. in which it is concluded that: "it [observed variation in NMR relaxation rates upon ultra dilution] might merely reflect a trivial air-dependent phenomenon, or an unsuspected bias, and should not be extrapolated to the so-called memory of water, often alleged to explain the effectiveness of homeopathy."

Some homeopaths believe that there might be an effect of successive shaking on water structure leading to "clustering" of water molecules. This contradicts the dominant scientific view that motions in liquid water are on the picosecond (10⁻¹² second) time scale and that such clusters could not live longer than a few picoseconds.

People sometimes wonder if the water used to make homeopathic medicines already has other memory imprints from its history prior to use in medicine. However, the water used by homeopathic manufacturers undergoes double-distillation, a process that homeopaths contend eliminates or substantially reduces previous memory. This raises the question: how do homeopaths know that this reduction is sufficient? If the presence of homeopathic qualities is below detection threshold, then surely the absence of such qualities is also undetectable.

In brief, for homeopathy to receive serious scientific consideration, there needs to be plausible explanations for the following:

• how the process of manufacturing a homeopathic remedy could yield a biologically active substance or solution
• why the principle of similars might apply in the case of homeopathic remedies
• how a biological mechanism could have evolved to recognize the specific nature of homeopathic remedies

There also needs to be

• clear and irrefutable evidence for the efficacy of homeopathic remedies, evidence that cannot be explained by placebo effects

These stringent demands are often summarised by the maxim "Extraordinary claims require extraordinary proof".

Meanwhile, homeopaths, working towards an elucidation of the effectiveness of their medicines, complain that they are up against a double standard in medicine and science. They point out that there is a long history of conventional medical treatments that are applied with positive effects, although their mechanism of action is not known. Only relatively recently, for instance, has it been understood how aspirin works, but before that doctors used it regularly despite an inadequate understanding of its actual mechanism. In due time, the homeopathic community asserts, the scientific basis of their methods will be unveiled.

Clinical trials testing the efficacy of homeopathic remedies

The “balance of evidence” as to whether homeopathy has any effects other than placebo effects depends on who is balancing the evidence. Homeopaths strongly value the evidence of their own experience in treating patients, supported by the satisfaction reported by their patients in surveys; they believe that this is sufficient evidence of efficacy, but also state that most published clinical trials have shown some beneficial effects. A 1991 global meta-analysis of homeopathic clinical trials published in the BMJ (British Medical Journal) of 105 trials, 81 with positive outcomes, concluded that the placebo response could not explain the positive responses, and another meta-analysis published in the Lancet in 1997 drew similar conclusions. Several meta-analyses evaluating the homeopathic treatment of specific diseases have found positive results, including the treatment of childhood diarhea, some post-surgical conditions and respiratory allergies .

Other meta-analyses have suggested that the effect from a homeopathic remedy was no better than a placebo The Cochrane Collaboration is an organisation that publishes meta-analyses of trial results, and most of their analyses of homeopathic treatments indicate some treatment benefits but not adequate statistically significant benefit. The most supportive of their analyses is of the possible benefits of Oscillococcinum for influenza and influenza-like syndromes.

Why do most trials report positive outcomes for homeopathy, but some show no effect, and how is it that the positive evidence does not persuade most scientists and leaders of academic medicine? In the U.S.A., The National Center for Complementary and Alternative Medicine (NCCAM) administers public-funded research into alternative medicine , and some studies have reported positive outcomes, but NCCAM's acting deputy director, Jack Killen, said, in a Newsweek article, "There is, to my knowledge, no condition for which homeopathy has been proven to be an effective treatment." . In the U.K., the NHS recognizes that there have been about 200 randomised controlled trials evaluating homeopathy, some show efficacy of treatment and some don't. They conclude, "Despite the available research, it has proven difficult to produce clear clinical evidence that homeopathy works".

Homeopaths believe that such attitudes reflect bias against alternative medicine, and that because homeopathy does not lend itself to controlled trials, those with a negative outcome may be false negatives.

According to critics of homeopathy, the published trials of specific homeopathic remedies have been mostly small and flawed in design While many of these have indicated positive effects, generally, trials that are larger high-quality trials have tended to show little or no statistically significant effects, as was concluded by the authors of the second Lancet study cited above when they re-analyzed these trials Homeopaths respond that the vast majority of the larger high-quality trials simply tested a single homeopathic medicine, without the requisite individualization of treatment common to homeopathic treatment.

But this does not explain why small trials should have more strongly positive outcomes than large trials. In fact this is a feature of trials of conventional medicine also – and it is believed that the explanation lies mainly in ‘’publication bias’’ – the tendency of trial outcomes to be published only if the outcome is clearly positive; many small trials with negative or inconclusive outcomes simply go unreported, because they are thought to be uninteresting.

In 1999, the government of Switzerland, for a trial period of 5 years, allowed health costs for treatment with homeopathy and four other CAM modalities to be reimbursed under the country’s compulsory health insurance scheme, and set up a programme to evaluate the cost-effectiveness of these treatments (the Complementary Medicine Evaluation Programme (Programm Evaluation Komplementärmedizin, PEK). Under this programme, a team of scientists and practitioners, including a homeopath, conducted an innovative meta-analysis that became the single most cited study of homeopathy, arousing considerable media attention and a storm of protest from homeopaths. The study, which was also published in the Lancet (by Shang et al.) adopted a novel approach; whereas traditional meta-analyses have tried to combine all studies of a given condition, this was a "global" meta-analysis of homeopathy testing the hypothesis that all reported effects of homeopathic remedies are placebo effects. If so, the authors reasoned, then the reports of positive effects reflect publication bias, and if this is the case then the magnitude of such effects should diminish with sample size and study quality, and for the largest and best studies there should be no effect.

They analyzed 110 placebo-controlled homoeopathy trials and 110 matched conventional-medicine trials. Overall, the conventional medicine trials showed some real effect of treatment, in that some effect was still present in the largest and best trials, but the trials of homeopathy remedies did not. The authors concluded that their analysis was consistent with homeopathy being no better than placebo treatment, and controversially suggested that no further research on homeopathy is necessary. The article was accompanied by an unsigned editorial entitled “The end of homeopathy”" and a signed editorial by Jan Vandenbroucke, professor of clinical epidemiology, at Leiden University, the Netherlands This does not mean that that people treated with homeopathy do feel better as a result - the clinical literature clearly shows this, but Vandenbroucke suggested that this could be because its practitioners treatments spend more time with people than doctors do. The Lancet subsequently published a selection of critical correspondence, and received an angry open letter from the Swiss Association of Homoeopathic Physicians (SVHA). which declared:

“The meta-analysis may be statistically correct. But its validity and practical significance can be seen at a glance: not one single qualified homoeopath would ever treat one single patient in clinical practice as presented in any of the 110 analysed trials! The study cannot give the slightest evidence against homoeopathy because it does not measure real individual (classical) homoeopathy. It confounds real homoeopathic practice with distorted study forms violating even basic homeopathic rules.”

In the Shang et al. review, 21 of the homeopathic trials were judged of “high quality”; these studies, overall, showed a benefit of homeopathic treatment. In the final phase of analysis, the researchers included only the largest of these studies; the 8 largest homeopathic trials showed that homeopathic treatment was comparable with a placebo, while 6 similarly large conventional medical trials were not compatible with a placebo effect. Of the 8 largest and best homeopathic trials, only one used an individualized approach to treatment, the other seven used a single medicine prescribed to homeopathic treated subjects. Such non-individualized treatment is common in the larger clinical trials (one of the trials even tested a rarely used homeopathic medicine, Thyroidinum, in the treatment of weight-loss, in a previously untested treatment protocol).

Subsequent critics of the Shang et al. analysis have questioned how definitive it actually is, noting that it involved subjective judgements of study quality. The authors of an article in the Journal of Clinical Epidemiology say "This result can be interpreted differently. Following Shang's perspective it can be explained by small study bias (which includes publication bias). In contrast, one may hypothesize that Shang's result is falsely negative." The authors noted that four of the 21 best trials selected by Shang et al. dealt with preventing or treating muscle soreness—these consistently found no benefits to homeopathy, so if it is accepted that homeopathy is not useful in this condition, the remaining 17 trials show an overall significant effect, mainly determined by two trials on influenza-like diseases. Thus they argue that it is still possible that homeopathy might be effective for some conditions and not for others.

Proponents of homeopathy also note that some of the conventional medical studies analysed by Shang et al. may have shown a treatment effect but that some of these have since been withdrawn because of side effects found subsequently. Critics of homeopathy agree—they say that in conventional medicine, treatments are abandoned when trials show them to be ineffective or unsafe, or when a better drug is found; by contrast, no homeopathic treatment has ever been withdrawn after a trial showed it to be ineffective.

Safety

The highest ideal of cure is the speedy, gentle, and enduring restoration of health by the most trustworthy and least harmful way (Samuel Hahnemann)

The U.S. Food and Drug Administration's view of homeopathy is that there is no real concern about the safety of most homeopathic products because of the extremely small dosages. The F.D.A. has deemed that the vast majority of homeopathic medicines are over-the-counter drugs (OTC), that is, drugs that do not need a doctor's prescription and that are safe enough for home care. In the U.S.A., homeopathic remedies must have at least one indication for usage for a disease or condition that is self-limiting and that does not require medical diagnosis or medical monitoring. The European Union allows homeopathic medicinal products, if they are at least 3X, that is, they may not contain either more than one part per 10 000 of the mother tincture or more than 1/100th of the smallest dose of an active substance. No specific therapeutic indication may be given on the label of the product. Some physicians, however, maintain that homeopathic treatment is relatively unsafe, because it might delay conventional medical treatment. Homeopaths respond to these concerns by noting that using homeopathic medicines can delay or reduce the use of conventional medicines that are ineffective and dangerous.

Probably every modern pharmacologist would agree with Hahnemann that the drugs prescribed by conventional physicians of the 19th century were at best ineffective and often dangerous. However, some homeopaths question whether even modern medical drugs are safe and effective, and recommend homeopathic remedies instead. For example, a 2006 survey by the U.K. charitable trust Sense About Science revealed that homeopaths were advising travelers against taking conventional anti-malarial drugs, instead recommending they take a homeopathic remedy. Even the director of the The Royal London Homeopathic Hospital condemned this:

I'm very angry about it because people are going to get malaria - there is absolutely no reason to think that homeopathy works to prevent malaria and you won't find that in any textbook or journal of homeopathy so people will get malaria, people may even die of malaria if they follow this advice.

Another concern of conventional physicians is that some homeopaths discourage the use of vaccines. Many homeopaths think that vaccination for common diseases, such as measles and chicken-pox, is unnecessary, and some believe that vaccines can even be damaging to health, because of the mercury and aluminum in them, because the bacterium or virus in the vaccine may neither be dead nor weak enough, and/or because some childhood infectious diseases may strengthen immune responsiveness. Such advice is considered irresponsible by many public health professionals, who assess the benefits of vaccination as vastly outweighing the risks. (see reference for explanation of the risks associated with measles and chicken-pox).