Allopathic medicine

Allopathic medicine, or allopathy, refers to science-based, modern medicine. There are regional variations in usage of the term. In the United States, the term is used to contrast with osteopathic medicine, especially in the field of medical education.
The terms were coined in 1810 by the inventor of homeopathy, Samuel Hahnemann. It was originally used by 19th-century homeopaths as a derogatory term for heroic medicine, the traditional European medicine of the time and a precursor to modern medicine, that did not rely on evidence of effectiveness. Heroic medicine was based on the belief that disease is caused by imbalance among the four "humours" (blood, phlegm, yellow bile, and black bile) and sought to treat disease symptoms by correcting that imbalance, using "harsh and abusive" methods to induce symptoms seen as opposite to those of diseases rather than treating their underlying causes: disease was caused by an excess of one humour and thus would be treated with its "opposite".
Among homeopaths and other alternative medicine advocates, "allopathic medicine" now refers to "the broad category of medical practice that is sometimes called Western medicine, biomedicine, evidence-based medicine, or modern medicine." This description continued to be used to describe anything that was not homeopathy. The meaning implied by the label has never been accepted by conventional medicine and is still considered pejorative by some. William Jarvis, an expert on alternative medicine and public health, states that "although many modern therapies can be construed to conform to an allopathic rationale (e.g., using a laxative to relieve constipation), standard medicine has never paid allegiance to an allopathic principle" and that the label "allopath" was "considered highly derisive by regular medicine." Most modern science-based medical treatments (antibiotics, vaccines, and chemotherapeutics, for example) do not fit Samuel Hahnemann's definition of allopathy, as they seek to prevent illness, or alleviate an illness by eliminating its cause.
Etymology.
The terms "allopathic medicine" and "allopathy" are drawn from the Greek prefix "ἄλλος", "állos", "other," "different" + the suffix "πάθος", "páthos", "suffering".
History.
The practice of medicine in both Europe and North America during the early 19th century is sometimes referred to as heroic medicine because of the extreme measures (such as bloodletting) sometimes employed in an effort to treat diseases. The term "allopath" was used by Hahnemann and other early homeopaths to highlight the difference they perceived between homeopathy and the "conventional" heroic medicine of their time. With the term allopathy (meaning "other than the disease"), Hahnemann intended to point out how physicians with conventional training employed therapeutic approaches that, in his view, merely treated symptoms and failed to address the disharmony produced by underlying disease. Homeopaths saw such symptomatic treatments as "opposites treating opposites" and believed these methods were harmful to patients.
Practitioners of alternative medicine have used the term "allopathic medicine" to refer to the practice of conventional medicine in both Europe and the United States since the 19th century. In that century, the term allopath was used most often as a derogatory name for the practitioners of heroic medicine,<ref name="DOI 10.1177/0002716202583001002"></ref> a precursor to modern medicine that itself did not rely on evidence of effectiveness.
James Whorton discusses this historical pejorative usage: 
The controversy surrounding the term can be traced to its original usage during a heated 19th-century debate between practitioners of homeopathy and those they derisively referred to as "allopaths."
Hahnemann used "allopathy" to refer to what he saw as a system of medicine that combats disease by using remedies that produce effects in a healthy subject that are different (hence Greek root "allo-" "different") from the effects produced by the disease to be treated. The distinction comes from the use in homeopathy of substances that are meant to cause similar effects as the symptoms of a disease to treat patients ("homeo" - meaning similar).
As used by homeopaths, the term "allopathy" has always referred to the principle of treating disease by administering substances that produce other symptoms (when given to a healthy human) than the symptoms produced by a disease. For example, part of an allopathic treatment for fever may include the use of a drug which reduces the fever, while also including a drug (such as an antibiotic) that attacks the cause of the fever (such as a bacterial infection). A homeopathic treatment for fever, by contrast, is one that uses a diluted dosage of a substance that in an undiluted form would induce fever in a healthy person. These preparations are typically diluted so heavily that they no longer contain any actual particles of the original substance. Hahnemann used this term to distinguish medicine as practiced in his time from his use of infinitesimally small (or nonexistent) doses of substances to treat the spiritual causes of illness.
The "Companion Encyclopedia of the History of Medicine" states that "[Hahnemann] gave an all-embracing name to regular practice, calling it 'allopathy'. This term, however imprecise, was employed by his followers and other unorthodox movements to identify the prevailing methods as constituting nothing more than a competing 'school' of medicine, however dominant in terms of number of practitioner proponents and patients".
Contrary to the present usage, Hahnemann reserved the term "allopathic medicine" to the practice of treating diseases by means of drugs inducing symptoms unrelated (i.e., neither similar nor opposite) to those of the disease. He called the practice of treating diseases by means of drugs producing symptoms opposite to those of the patient "enantiopathic" (from the Greek "ἐνάντιος" (enántios), meaning "opposite") or "antipathic medicine". After Hahnemann's death, the term "enantiopathy" fell into disuse and the two concepts of allopathy and enantiopathy have been more or less unified. Both, however, indicate what Hahnemann thought about the medical practices of his time, rather than the ideas of the present. Conventional physicians of the 19th century had never assumed that the therapeutic effects of drugs were necessarily related to the symptoms they caused in the healthy (e.g. James Lind systematically tested several common substances and foods for their effect in treating scurvy in 1747 and discovered that lemon juice was specifically effective. He did not conduct any studies of these substances in healthy volunteers).
Current.
The term is used in the modern era to differentiate between two types of US medical schools (both of which teach aspects of science-based medicine and neither of which teach homeopathy): Allopathic (granting the MD title) and Osteopathic (granting the DO title).
Use of the term remains common among homeopaths and has spread to other alternative medicine practices. The meaning implied by the label has never been accepted by conventional medicine and is still considered pejorative by some. William Jarvis, an expert on alternative medicine and public health, states that "although many modern therapies can be construed to conform to an allopathic rationale (e.g., using a laxative to relieve constipation), standard medicine has never paid allegiance to an allopathic principle" and that the label "allopath" was "considered highly derisive by regular medicine".
Most modern science-based medical treatments (antibiotics, vaccines, and chemotherapeutics, for example) do not fit Samuel Hahnemann's definition of allopathy, as they seek to prevent illness, or remove the cause of an illness by acting on the cause of disease.