The founder and developer of homeopathy was Samuel Hahnemann, (1755-1843). He was a German physician and some of his concepts seem to appear early in medical history. He developed homeopathy after becoming dissatisfied with the medicine of the time. Treatments at that time included bleeding, purging, cupping and excessive doses of mercury. He stopped practicing medicine in about 1782 and began to seriously question the mechanisms his cohorts were using.

He viewed disease as a matter of vital force or spirit. One of the earliest speculations of recorded medical history is the concept of the vital spirit and similar forces form the probable basis for any number of metaphysical health practices. It was thought to be a nonmaterial "force" that maintains life and for which there is no objective evidence. "The cause of our maladies cannot be material, since the least foreign material substance, however mild it may appear to us, if introduced into our blood-vessels, is promptly ejected by the vital force, as though it were a poison. no disease, in a word, is caused by any material substance, but that every one is only and always a peculiar, virtual, dynamic derangement of the health", according to Hahnemann.

Paying attention to the symptoms rather than to the external causes of a disease is believed to be more important. If one knew the specific symptoms of an illness, then all one had to do was find a substance or substances that induced the same symptoms in a healthy individual. This is referred to as, "Hahnemann's Principle of Similars". At one time there were experiments that supported this notion, such as the work of Pasteur and Koch on inoculations, where very tiny amounts of weakened disease-causing microbes were used.

To test this notion Hahnemann and his followers tested the effects of almost 100 substances on themselves. This is a process known as "proving". The usual procedure was for a healthy person to ingest a small amount of a particular substance and then attempt to cautiously note any type of reaction or symptom which included emotional or mental reactions that might occur. By using this method, he "proved" that some substances were effective for treatment for a particular symptom. In one controlled study, healthy people reported similar symptoms whether given a homeopathic dilution of belladonna or a placebo.

Hahnemann believed that homeopathic remedies must be right for each individual person and prescribed them according to body type and personalities, which was based on the ancient humoral theories of Galen. The theories stated that there were four body types and personalities, based on which body "humor" predominated: blood (sanguine, warm-hearted and volatile,) black bile (melancholic, sad), yellow bile (choleric, quick to anger and to action) and phlegm (phlegmatic, sluggish and apathetic). He also said there were a few corresponding primary causes of acute and chronic illnesses, which he called "miasms". The first miasm is known as "psora" (itch) refers to a general susceptibility to disease and may be considered the source of all chronic diseases. The other two miasms are venereal diseases syphilis and sycosis (gonorrhea). These three conditions were thought to be the causes of at least 80 percent of all chronic diseases.

One good thing most definitely did come from homeopathy and that was an end to some of the ridiculous treatments. Some of the treatments were more dangerous than the diseases. Homeopathy may have helped speed the demise of such treatments and it provided the ideas and source for more useful drugs and treatments. Some early scientists stated that homeopathy led them to important pharmacological discoveries.