Homœopathy (Home' - ee - AH' - puh - thee; sometimes spelled homeopathy) is a system of healthcare developed and introduced by the German physician Samuel Hahnemann in the late 1700s. At its heart is the phenomenon of cure by similars, where a substance that could produce disease in a healthy person (when given in excess) is used to invite a healing response in someone presenting with a similar disease. Homœopathy takes its name from this phenomenon of cure by similars; from the Greek, homœo = "similar", pathos = "suffering".

This use of cure by similars actually predates homœopathy by several centuries. Hippocrates records the use of this approach to healing (c. 400BC in Greece), and we find references to it from the Oracle of Delphi, from Indian medical texts as much as 4,000 years old, and from ancient Chinese medical texts. Celsus, a physician of the Greek classical period, and Theophrastus, a Swiss physician of the 16th century, received renown for their effectiveness as physicians relying on this approach.

Hahnemann was trained as a conventional physician at the University in Leipzig, Germany. Discouraged by the medicine of his day, and distraught at the near demise of his daughter under the care of a conventional physician, Hahnemann left the practice of medicine to write and translate books. In entertaining the question of what a viable system of medicine would involve, he came back to the historical references to cure by similars in the Hippocratic writings. From his own experiments with Chinchona bark (from a Peruvian tree, the source of Quinine), he convinced himself that Chinchona's effectiveness in treating some cases of malaria resulted from its ability to create a similar disease to which the body could respond, resulting in a healing response to both the medicine-induced condition and the malaria.

Hahnemann went on to apply this principal of cure by similars to other conditions, using many other remedies, and came to observe it as a universal law of cure; he coined the expression "Similia Similibus Curentur" ("Let likes cure likes") as the cornerstone of his homœopathic philosophy.

A second cornerstone of homœopathy is the minimum dose. The incredibly tiny doses we use in treatment came about through careful systematic experimentation by early homœopaths. While larger doses could often elicit the healing responses desired, this would often be accompanied by undesirable side effects of the medications. Reducing the dose served to minimize or eliminate these undesirable side effects. Much to the surprise of Hahnemann and his colleagues, these smaller doses also often worked much more effectively in bringing about a healing response. Although the "logic" of using such tiny doses may defy us, we observe it to work in practice and continue to rely on these minimum doses today.

The third cornerstone of homœopathy is the use of a single remedy at any one time. Inviting a healing response can be confusing to the body, with unpredictable results, inviting several responses simultaneously. Although some practitioners have deviated on this point and use combinations of remedies, Hahnemann abandoned this approach after experimenting with it himself.

We learn about the properties of our remedies through provings. In a proving, a number of healthy people are given excessive doses of a particular remedy, and the symptoms they develop are carefully recorded. These patterns of symptoms have been systematically recorded in books we refer to as materia medica. This remedy could then be used to treat a person presenting with an illness which had a similar pattern of symptoms.

The prescription of a particular remedy will be based upon the totality of symptoms of the individual. In taking a case, the characteristics and behavior of each symptom of the patient are recorded and used to find a matching remedy. Unlike conventional medicine, which might consider some symptoms of the individual to be unrelated to the "condition" to be treated, homœopathy views disease as a disharmony of the whole person and considers the state of the whole person – physically, mentally, and emotionally – when finding an appropriate remedy.

Homœopathy was a popular system of medical care in the United States during the 19th century (my wife's great-grandfather was a homœopathic physician in Madison, Maine, having graduated from Boston University Medical School, which was a homœopathic medical school in those days). Sociopolitical factors led to its decline in the U.S. in the early 1900s, but it has remained a prominent form of medical care in England, Germany, France, India, and parts of South America. A handful of professional practitioners, and many families with their remedy kits and homecare manuals, have kept homœopathy alive in the U.S. through the time of its current resurgence.