The reasons why particular substances were selected as homeopathic remedies are complex and varied. Many were familiar from traditional Western folklore or herbal lore. Some, such as mercury, were used in contemporary conventional medicine. Others included minerals or elements that had been used as nutritional supplements, such as zinc. Out of curiosity, or because they had a long herbal tradition or were known to have a strong, even toxic, effect, different substances were tried and the information cataloged. The greatest influence came initially from herbalists in Europe but, as knowledge grew of the medicinal traditions of other cultures, more substances were tested for their homeopathic potential. European explorers and settlers filtered back information amassed on their travels. Dr. Constantine Hering, for instance, visited South America and discovered the healing properties of the bushmaster snake.

Hahnemann set down strict guidelines for testing, or “proving,” potential remedies. This term developed from Prüfung, the German word for a trial. A set of volunteers, or “provers,” take a trial substance in different strengths, or potencies, and make a detailed, archetypal “character” emerges. Essential or “keynote” characteristics, both mental and physical, can be established to give a thumbnail summary, enabling homeopaths to recognize cases where a particular remedy is appropriate. Dr. James Tyler Kent carried out a great deal of research to enlarge knowledge of the remedies in the daily record of their moods, sensations, and any symptoms that develop. Symptoms are categorized as general, relating to a temperamental picture, or specific, affecting a particular part of the body. Surrounding or provoking circumstances, and triggers that make symptoms better or worse, are all noted. Certain general, physical, and psychological affinities appear more evident than others, and some symptoms will be very common among the provers; for example, a headache first thing in the morning that gets better after eating, or indifference to loved ones. These are “first-line” symptoms. Other symptoms may be experienced by only a few, or even one, prover. These are known respectively as “second-line” and “third-line” symptoms. Any symptom that can be shown to be unlike the person’s usual state of health will be recorded. This information is then compiled to produce a “symptom picture” that takes into account the potential variations produced by different provers’ constitutional types. Often this will then be compared with information about the substance and its characteristics, possibly from its prior use within herbal or folk medicine, or from knowledge of its toxicology, to deepen understanding of the remedy. As understanding of each remedy’s “symptom picture” grows, an materia medica, and his work has been built on and augmented by many other practitioners.

Beyond the individual remedies, it is possible to make connections between remedies and to establish group relationships. Studying the group of remedies based on potassium or calcium compounds, for example, reveals themes, such as physical weakness with all Kalium remedies, or sensitivity and shyness with all Calcium remedies. This thematic analysis is most obvious in clear categories like families of the periodic table, which have recently been researched by the British homeopath Jeremy Sherr. Relationships between plants within the same botanical family, or between animals with common links, can also be found. For example, all snake-based remedies tend to affect the blood and nervous system, and are for highly oversensitive individuals. The Indian homeopath Rajan Sankaran is working on an approach to case-taking that emphasizes the underlying sensations a patient feels, and linking this to a framework running through the animal, plant, and mineral kingdoms and families that form the basis of remedies. The breadth of information available from some of the old provings is not complete, whereas other provings are very well documented. New provings tend to be carefully managed and usually give a full picture.

Between the 1st and 5th centuries CE the Romans made further developments in medicine. They introduced more herbs into the pharmacopeias, improved public hygiene, and observed the structure and function of the human body.

The Swiss physician and alchemist Paracelsus (1493–1541) began to develop his theories did the study of medicine start to evolve again. Paracelsus revived the ancient Greek theory of the Doctrine of Signatures, which was based on the premise that the external appearance of a plant indicated the nature of its healing properties.

His exploration of the chemical and medicinal properties of many substances, and his advocacy of the Hippocratic concept of “like cures like,” also made Paracelsus a key figure in the development of homeopathy.

The true healers of the era, before the advent of homeopathy, were the herbalists. Mostly female, they practiced an art passed through the generations that respected the fundamental ability of the body to heal itself. The patient of that era was fortunate to be in the hands of such a healer. With nutritious broths and simple herbal medicines, the patient’s chances of recovery were actually enhanced by the treatment.

These herbalists were largely opposed by the medical establishment. They were belittled as backwards, uneducated, or even dangerous. Many women persecuted as witches were actually herbal healers, performing their services, often without remuneration, for the welfare of the community.

This was the cultural and scientific milieu in which the German doctor Samuel Christian Hahnemann (1755–1843) began practicing in 1780. He continued in practice for nine years, during which time he became increasingly disillusioned with the harsh medical methods of the day. In articles written to supplement his income, Hahnemann attacked the extreme medical practices of the day, advocating instead good public hygiene, improved housing conditions, better nutrition, fresh air, and exercise.

Hahnemann’s work gradually brought about the establishment of new type of medicine. In 1796 he published his first book on the subject, entitled A New Principle for Ascertaining the Curative Powers of Drugs and Some Examinations of Previous Principles. He called his new system “homeopathy,” from the Greek homeo meaning “similar” and pathos meaning “suffering.

In 1810 he set out its principles in The Organon of Rationale Medicine, and two years later he began teaching homeopathy at the University of Leipzig. During the course of his lifetime, Hahnemann proved about 100 remedies, and also continued to develop and refine the theory and practice of the system.

During the 19th century, homeopathy spread rapidly across Europe to Asia and the Americas. In the US, Dr. Constantine Hering (1800–80) and Dr. James Tyler Kent (1849–1916) were responsible for popularizing the therapy and introducing new ideas and practices. By the time of Hahnemann’s death in 1843, homeopathy was firmly established in many parts of the world, although there remained antagonism and distrust between the advocates of conventional medicine and those of homeopathy.

The homeopaths formed the first national medical association, the American Institute of Homeopathy (AIH), in 1844. This association exists to this day representing medical doctors who practice homeopathy. The conventional medicine was not to be outdone. They countered by forming the American Medical Association (AMA) in 1846. Letters between the founding members of the AMA show that one of the main purposes for the formation of the AMA was to oppose the spread and practice of homeopathy. Early AMA members also opposed the spread of osteopathy (a medical system using manipulation of the joints and other tissues).

This contentious relationship continued throughout the 1800s. Homeopathy continued to spread and homeopathic medical schools were started. Despite the often desperate and unprofessional attempts by the AMA to discredit and stop homeopathy, by the turn of the century one in four physicians in America was a homeopath.

During the late 20th century there has been a resurgence in the popularity of homeopathy, possibly due to disenchantment with aspects of conventional medicine. In many countries, particularly in central Europe, its popularity never waned to the same extent as in the UK and US, although differences in practice have evolved.

Since the 1970s, awareness of an interest in homeopathy has steadily increased. Patients frustrated with the limitations, side-effects, and high costs of conventional medicine actively seek health-oriented alternatives.

Homeopathy is a logical choice. It can be used in patients with both acute and chronic conditions, has few, if any, side-effects, and is inexpensive.

In America, the homeopaths of the past were almost all medical doctors. Today, medical doctors practicing homeopathy represent a minority of the practitioners. Many practitioners hold licenses as naturopaths, chiropractors, nurse practitioners, physician assistants, and acupuncturists. There are also a growing number of professional homeopaths, persons with no formal medical training or licensing outside of their homeopathic training. Some of the most renowned homeopaths in the world today fall in this category.